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Oscillatory synchrony as a mechanism of attentional processing
... Feedback visual signals are expressed as synchronized LFP oscillations in the alphafrequency band (~7-15 Hz) Michalareas et al. 2016; van Ede et al. 2015;van Kerkoerle et al. 2014). Interestingly, synchronized gamma-frequency band LFP oscillations have been implicated in both bottom-up/feedforward and top-down/feedback corticocortical communication (Gregoriou et al. 2009;Gregoriou et al. 2015;Michalareas et al. 2016;Richter et al. 2017;van Kerkoerle et al. 2014). Furthermore, gamma-frequency LFPs are also modulated by visual attention, especially in extrastriate visual cortical areas (Bauer et al. 2014;Bosman et al. 2012;Buffalo et al. 2010;Chalk et al. 2010;Fries et al. 2001Fries et al. , 2008Gregoriou et al. 2009Gregoriou et al. , 2015Siegel et al. 2008;Taylor et al. 2005;Vinck et al. 2013). ...
... Interestingly, synchronized gamma-frequency band LFP oscillations have been implicated in both bottom-up/feedforward and top-down/feedback corticocortical communication (Gregoriou et al. 2009;Gregoriou et al. 2015;Michalareas et al. 2016;Richter et al. 2017;van Kerkoerle et al. 2014). Furthermore, gamma-frequency LFPs are also modulated by visual attention, especially in extrastriate visual cortical areas (Bauer et al. 2014;Bosman et al. 2012;Buffalo et al. 2010;Chalk et al. 2010;Fries et al. 2001Fries et al. , 2008Gregoriou et al. 2009Gregoriou et al. , 2015Siegel et al. 2008;Taylor et al. 2005;Vinck et al. 2013). Visual attention modulates neuronal activity across the visual hierarchy with less modulation in LGN and V1 and greater modulation in higher extrastriate visual cortical areas (Ito and Gilbert 1999;Luck et al. 1997;McAdams and Reid 2005;McAlonan et al. 2006;Motter 1993;O'Connor et al. 2002; Vanduffel et al. 2000). ...
... Second, based on predictions of the framework that feedforward visual signals are conveyed by beta-frequency oscillations (Bastos et al. 2014), we hypothesized that attentional enhancement of feedforward communication would be selective for beta frequencies. Third, also based on predictions of the framework that top-down attention signals are carried by alpha-and/or gamma-frequency oscillations Gregoriou et al. 2015;van Kerkoerle et al. 2014), we hypothesized that attentional enhancement of feedback communication would be selective for alpha or gamma frequencies. Fourth, based on predictions of the framework and the fact that feedback from V1 to the LGN is mediated by corticogeniculate neurons in layer 6, we hypothesized that attentional enhancement of feedback communication from V1 to the LGN would be greatest for alpha-and/or gamma-band interactions between the deep layers of V1 and the LGN. ...
Correlations and inferred causal interactions among local field potentials (LFPs) simultaneously recorded in distinct visual brain areas can provide insight into how visual and cognitive signals are communicated between neuronal populations. Based on the known anatomical connectivity of hierarchically organized visual cortical areas and electrophysiological measurements of LFP interactions, a framework for inter-areal frequency-specific communication has emerged. Our goals were to test the predictions of this framework in the context of the early visual path¬ways and to understand how attention modulates communication between the visual thalamus and primary visual cortex. We recorded LFPs simultaneously in retinotopically aligned regions of the visual thalamus and primary visual cortex in alert and behaving macaque monkeys trained on a contrast-change detection task requiring covert shifts in visual spatial attention. Coherence and Granger-causal interactions among early visual circuits varied dynamically over different trial periods. Attention significantly enhanced alpha, beta, and gamma frequency interactions, often in a manner consistent with the known anatomy of early visual circuits. However, attentional modulation of communication among early visual circuits was not consistent with a simple static framework in which distinct frequency bands convey directed inputs. Instead, neuronal network interactions in early visual circuits were flexible and dynamic, perhaps reflecting task-related shifts in attention.
... Previous studies have shown that specific cell types and network structures are associated with the generation of different oscillations [69]. Our study well investigated the oscillatory networks, and the findings might reveal potential mechanisms in oscillatory synchrony between intrinsic cortical structures. ...
... Our study well investigated the oscillatory networks, and the findings might reveal potential mechanisms in oscillatory synchrony between intrinsic cortical structures. Additionally, previous researches have provided much evidence that specific neurotransmitters can cause diverse effects on oscillatory synchrony across different brain areas, thus regulating various cognitive functions [69]- [72]. The results about altered synchronization via different oscillations could provide potential references in the neuropharmacology of MDD. ...
Dysconnectivity of large-scale brain networks has been linked to major depression disorder (MDD) during resting state. Recent researches show that the temporal evolution of brain networks regulated by oscillations reveals novel mechanisms and neural characteristics of MDD. Our study applied a novel coupled tensor decomposition model to investigate the dysconnectivity networks characterized by spatio-temporal-spectral modes of covariation in MDD using resting electroencephalography. The phase lag index is used to calculate the functional connectivity within each time window at each frequency bin. Then, two adjacency tensors with the dimension of time frequency connectivity subject are constructed for the healthy group and the major depression group. We assume that the two groups share the same features for group similarity and retain individual characteristics for group differences. Considering that the constructed tensors are nonnegative and the components in spectral and adjacency modes are partially consistent among the two groups, we formulate a double-coupled nonnegative tensor decomposition model. To reduce computational complexity, we introduce the lowrank approximation. Then, the fast hierarchical alternative least squares algorithm is applied for model optimization. After clustering analysis, we summarize four oscillatory networks characterizing the healthy group and four oscillatory networks characterizing the major depression group, respectively. The proposed model may reveal novel mechanisms of pathoconnectomics in MDD during rest, and it can be easily extended to other psychiatric disorders.
... Average inter-areal GC exceeded the bias estimate across the spectrum and showed two clear peaks, one in the alpha-beta range, peaking at 11 Hz, and one in the gamma band, peaking around 60 Hz. Previous studies have shown clear differences between alpha and beta rhythms (Wang, 2010;Bressler and Richter, 2014;Haegens et al., 2014;Gregoriou et al., 2015), however, the present analysis revealed one peak spanning across alpha and beta frequency ranges (similar to (Buffalo et al., 2011)), which we therefore refer to as the alpha-beta band. Peak frequencies were essentially identical in the two hemispheres. ...
... These earlier results from macaques agree fully with the present results for humans in the gamma band, but they agree only partly in the other frequency bands. Our present analysis in humans suggests that top-down influences are exerted by rhythms spanning alpha and beta frequency ranges, even though previous studies clearly suggest separate alpha and beta rhythms (Wang, 2010;Womelsdorf et al., 2014;Gregoriou et al., 2015). It is important to note that our analysis merely reveals whether directed influences in a frequency band relate to feedforward or feedback projections. ...
Primate visual cortex is hierarchically organized. Bottom-up and top-down influences are exerted through distinct frequency channels, as was recently revealed in macaques by correlating inter-areal influences with laminar anatomical projection patterns. Because this anatomical data cannot be obtained in human subjects, we selected seven homologous macaque and human visual areas, and we correlated the macaque laminar projection patterns to human inter-areal directed influences as measured with magnetoencephalography. We show that influences along feedforward projections predominate in the gamma band, whereas influences along feedback projections predominate in the alpha-beta band. Rhythmic inter-areal influences constrain a functional hierarchy of the seven homologous human visual areas that is in close agreement with the respective macaque anatomical hierarchy. Rhythmic influences allow an extension of the hierarchy to 26 human visual areas including uniquely human brain areas. Hierarchical levels of ventral- and dorsal-stream visual areas are differentially affected by inter-areal influences in the alpha-beta band.
... Third, a number of studies have reported frequency specific modulations in oscillatory synchrony with spatial and feature attention at multiple levels of visual processing (for a review see Gregoriou et al., 2015). These frequency specific modulations of local oscillatory synchrony include an enhancement of local oscillatory activity in gamma frequencies (30-60 Hz) among neurons encoding the attended stimulus Bichot et al., 2005;Tallon-Baudry et al., 2005;Taylor et al., 2005;Gregoriou et al., 2009b;Buffalo et al., 2011, but see Chalk et al., 2010, as well as a decrease with spatial attention in the alpha/beta frequency range (Thut et al., 2006;Fries et al., 2008;Siegel et al., 2008;Gregoriou et al., 2009b;Buffalo et al., 2011). ...
... Oscillatory activity reflects the rhythmic excitability fluctuations of a neuronal population and creates windows in time during which inputs are more effective in driving the neurons. These temporally constrained windows are the result of rhythmic inhibition within local networks of excitatory and inhibitory neurons (for a review see Gregoriou et al., 2015). Neuronal groups that are rhythmically active can synchronize their activities through phase-locking. ...
The ability to select information that is relevant to current behavioral goals is the hallmark of voluntary attention and an essential part of our cognition. Attention tasks are a prime example to study at the neuronal level, how task related information can be selectively processed in the brain while irrelevant information is filtered out. Whereas, numerous studies have focused on elucidating the mechanisms of visual attention at the single neuron and population level in the visual cortices, considerably less work has been devoted to deciphering the distinct contribution of higher-order brain areas, which are known to be critical for the employment of attention. Among these areas, the prefrontal cortex (PFC) has long been considered a source of top-down signals that bias selection in early visual areas in favor of the attended features. Here, we review recent experimental data that support the role of PFC in attention. We examine the existing evidence for functional specialization within PFC and we discuss how long-range interactions between PFC subregions and posterior visual areas may be implemented in the brain and contribute to the attentional modulation of different measures of neural activity in visual cortices.
... The action potentials of synchronized pre-synaptic neurons arrive at the post-synaptic dendrites closer in time and sum up more effectively than those from asynchronous pre-synaptic neurons, hence increasing their downstream impact. For this reason, synchronization of neuronal firing could represent a top-down attentional mechanism to prioritize processing of attended, relevant stimuli over competing, irrelevant ones (for recent reviews, see Fries, 2015;Gregoriou et al., 2015). ...
... From a theoretical perspective, post-synaptic processing stages would benefit from strongly synchronized pre-synaptic input (Engel et al., 2001). In particular, pre-synaptic neuronal groups that synchronize their firing more efficiently in response to attended stimuli can increase their post-synaptic drive, thereby facilitating the processing of attended stimulus features in downstream regions (Gregoriou et al., 2015). The attentional enhancement of gamma power in V4 observed here could thus reflect the increased efficacy by which the representation of attended stimuli in early visual cortex is propagated onto higher-order visual areas (Fries, 2015). ...
Oscillatory synchronization in the gamma frequency range has been proposed as a neuronal mechanism to prioritize processing of relevant stimuli over competing ones. Recent studies in animals found that selective spatial attention enhanced gamma-band synchronization in high-order visual areas (V4) and increased the gamma peak frequency in V1. The existence of such mechanisms in the human visual system is yet to be fully demonstrated. In this study, we used MEG, in combination with an optimised stimulus design, to record visual gamma oscillations from human early visual cortex, while participants performed a visuospatial attention cueing task. First, we reconstructed virtual sensors in V1/V2, where gamma oscillations were strongly induced by visual stimulation alone. Second, following the results of a statistical comparison between conditions of attention, we reconstructed cortical activity also in inferior occipital-temporal regions (V4). The results indicated that gamma amplitude was modulated by spatial attention across the cortical hierarchy, both in the early visual cortex and in higher-order regions of the ventral visual pathway. In contrast, we found no evidence for an increase in the gamma peak frequency in V1/V2 with attention. The gamma response tended to peak earlier in V1/V2 than in V4 by approximately 70 ms, consistent with a feed-forward role of gamma-band activity in propagating sensory representations across the visual cortical hierarchy. Together, these findings suggest that differences in experimental design or methodology can account for the inconsistencies in previous animal and human studies. Furthermore, our results are in line with the hypothesis of enhanced gamma-band synchronization as an attentional mechanism in the human visual cortex.
... For explaining ␥-oscillations in visual cortex, two mechanisms are deemed plausible: interneuron network gamma (ING) and pyramidal-interneuron network gamma (PING). Whether ING or PING mechanisms underlie oscillations in the visual cortex is still debated and might depend on task requirements (Tiesinga and Sejnowski 2009;Isaacson and Scanziani 2011;Buzsáki and Wang 2012;Gregoriou et al. 2015), but a combination of both seems most likely, considering the local connectivity structure (Haeusler and Maass 2007). In the current study, we focused on a "pure" ING-mechanism (no connections between excitatory and from excitatory to inhibitory subpopulations). ...
Selective attention allows to focus on relevant information, and to ignore distracting features of a visual scene. These principles of information processing are reflected in response properties of neurons in visual area V4: If a neuron is presented with two stimuli in its receptive field, and one is attended, it responds as if the non-attended stimulus was absent (biased competition). In addition, when the luminance of the two stimuli is temporally and independently varied, local field potentials are correlated with the modulation of the attended stimulus and not, or much less, correlated with the non-attended stimulus (information routing). To explain these results in one coherent framework, we present a two-layer spiking cortical network model with distance-dependent lateral connectivity and converging feed-forward connections. With oscillations arising inherently from the network structure, our model reproduces both experimental observations. Hereby, lateral interactions and shifts of relative phases between sending and receiving layers (communication through coherence) are identified as the main mechanisms underlying both, biased competition as well as selective routing. Exploring the parameter space, we show that the effects are robust and prevalent over a broad range of parameters. In addition, we identify the strength of lateral inhibition in the first model layer as crucial for determining the working regime of the system: Increasing lateral inhibition allows a transition from a network configuration with mixed representations to one with bistable representations of the competing stimuli. The latter is discussed as a possible neural correlate of multistable perception phenomena such as binocular rivalry.
Copyright © 2014, Journal of Neurophysiology.
... During attention tasks, gamma rhythms display the opposite behavior of alpha rhythms as gamma power is enhanced in task-relevant cortical areas (Figure 7). Attending to a location or to a feature is accompanied with increased gamma power in the visual area responsible for processing of this location or feature (human and monkey studies reviewed in Gregoriou, Paneri, and Sapountzis 2015). Electrocorticography data have shown enhanced gamma power in the auditory cortex when attending a sound or in the somatosensory cortex when attending tactile stimulation (Ray et al. 2008). ...
Attention is the cognitive ability which allows us to select and preferentially process relevant information in our environment. It relies on a balance between top-down and bottom-up processes and is heavily influenced by the ongoing arousal levels. Thereby, salient sounds in our environment can both hinder our performance during a task by capturing our attention or on the contrary boost our performance by triggering a transient increase in arousal. Attentional mechanisms are disturbed in numerous neurological and psychiatric disorder. Migraine is a neurological disorder which is not limited to recurrent and severe headaches: it is also characterized by sensory hypersensitivity which climaxes during migraine attack but also persists at a lower level in the pain-free period. Recent studies suggest that the attentional process of sensory inputs is dysfunctional in migraine: a deficient attentional filter may participate to sensory symptoms associated with the disorder. The aim of this work was made possible in part thanks to MEG and EEG recordings during a competitive attention task designed to evaluate conjointly voluntary attention, involuntary attention and phasic arousal. First, we attempted to isolate an electrophysiological marker of phasic increases in arousal triggered by the onset of salient sounds among healthy participants. The early-P3, an event-related response classically associated to attention capture, turned out to be a good candidate as a marker of phasic arousal. Then, we demonstrated that migraineurs presented a disrupted attentional processing of sounds, namely at the level of bottom-up attention and top-down inhibitory processes. These results were corroborated by a questionnaire study which revealed that migraineurs complain about attention difficulties in the everyday life and that these difficulties correlate with the sensory disturbances they experience. Finally, we aimed to detect anomalies of brain structure in migraine by analyzing newly acquired anatomical MRI and diffusion tensor imaging data, which we confronted to previous results of the literature. Neither the analysis of our anatomical data, nor the meta-analysis of the literature provided convincing evidence of an abnormal brain structure in migraine. This work provides new insights in the understanding of sensory symptoms in migraine and in parallel, offers a new tool to investigate phasic arousal.
... Increased gamma synchronization with spatial and feature attention has been observed in visual (Siegel et al. 2008), somatosensory (Bauer et al. 2006), frontal (Gregoriou et al. 2009) and parietal (Saalmann et al. 2007) cortices. It has been noticed that, gamma frequency enhancements were observed in tasks that required a relatively long sustained attention period suggesting that expectation and anticipation might be crucial factors for the emergence of gamma frequency synchronization (Gregoriou et al. 2015). In the case of large reward trials in our study, the monkeys paid more attention to the stimulus associated with the large reward and anticipated the large amount of reward at the end of trials. ...
The interplay between the prefrontal cortex (PFC) and striatum has an important role in cognitive processes. To investigate interactive functions between the two areas in reward processing, we recorded local field potentials (LFPs) simultaneously from the two areas of two monkeys performing a reward prediction task (large reward vs small reward). The power of the LFPs was calculated in three frequency bands: the beta band (15–29 Hz), the low gamma band (30–49 Hz), and the high gamma band (50–100 Hz). We found that both the PFC and striatum encoded the reward information in the beta band. The reward information was also found in the high gamma band in the PFC, not in the striatum. We further calculated the phase-locking value (PLV) between two LFP signals to measure the phase synchrony between the PFC and striatum. It was found that significant differences occurred between PLVs in different task periods and in different frequency bands. The PLVs in small reward condition were significant higher than that in large reward condition in the beta band. In contrast, the PLVs in the high gamma band were stronger in large reward trials than in small trials. These results suggested that the functional connectivity between the PFC and striatum depended on the task periods and reward conditions. The beta synchrony between the PFC and striatum may regulate behavioral outputs of the monkeys in the small reward condition.
... Endogenous signals representing exploratory saccades (Hoffman et al., 2013;Jutras et al., 2013), fixations (Rajkai et al., 2008), and erroneous expectations of rewards (Hyman et al., 2011) can also serve as ''internal cues'' that can reset phase. In recent year, many notable reviews on oscillatory coordination have detailed its neurophysiological underpinnings (Buzsáki, 2006;Wang, 2010;Lisman and Jensen, 2013;Womelsdorf et al., 2014b), implications for coding (Panzeri et al., 2010;Akam and Kullmann, 2014;Fries, 2015), emergence when attention, decision making and choice demands increase (Womelsdorf et al., 2010b;Siegel et al., 2012;Gregoriou et al., 2015;Watrous et al., 2015b), as well as its clinical relevance (Thut et al., 2011;Voytek and Knight, 2015). Here, we seek to extend these valuable contributions by surveying recently gathered evidence in light of dynamic resets, or realignments, of the phases of periodic activity fluctuations among neural circuits at the very moment when these circuits implement specific attention and memory functions. ...
Short periods of oscillatory activation are ubiquitous signatures of neural circuits. A broad range of studies documents not only their circuit origins, but also a fundamental role for oscillatory activity in coordinating information transfer during goal directed behavior. Recent studies suggest that resetting the phase of ongoing oscillatory activity to endogenous or exogenous cues facilitates coordinated information transfer within circuits and between distributed brain areas. Here, we review evidence that pinpoints phase resetting as a critical marker of dynamic state changes of functional networks. Phase resets (1) set a “neural context” in terms of narrow band frequencies that uniquely characterizes the activated circuits, (2) impose coherent low frequency phases to which high frequency activations can synchronize, identifiable as cross-frequency correlations across large anatomical distances, (3) are critical for neural coding models that depend on phase, increasing the informational content of neural representations, and (4) likely originate from the dynamics of canonical E-I circuits that are anatomically ubiquitous. These multiple signatures of phase resets are directly linked to enhanced information transfer and behavioral success. We survey how phase resets re-organize oscillations in diverse task contexts, including sensory perception, attentional stimulus selection, cross-modal integration, Pavlovian conditioning, and spatial navigation. The evidence we consider suggests that phase-resets can drive changes in neural excitability, ensemble organization, functional networks, and ultimately, overt behavior.
... Several cognitive functions, including attention and working memory, are associated with enhanced gamma oscillations (Fries et al, 2001;Gregoriou et al, 2015;Lundqvist et al, 2016). The role of gamma in cognition may result from regulation of millisecond-range synchrony between neuronal ensembles, dynamically establishing information channels between brain structures (Bartos et al, 2007;Benchenane et al, 2011). ...
Nicotine has strong addictive as well as procognitive properties. While a large body of research on nicotine continues to inform us about mechanisms related to its reinforcing effects, less is known about clinically relevant mechanisms that subserve its cognitive enhancing properties. Understanding the latter is critical for developing optimal strategies for treating cognitive deficits. The primary brain region implicated in cognitive functions improved by nicotine is the prefrontal cortex (PFC). Here we assessed the impact of nicotine on unit activity and local field potential (LFP) oscillations in the PFC of behaving rats. An acute dose of nicotine produced a predominantly inhibitory influence on population activity, a small increase in gamma oscillations, and a decrease in theta and beta oscillations. After a daily dosing regimen, a shift to excitatory-inhibitory balance in single-unit activity and stronger gamma oscillations began to emerge. This pattern of plasticity was specific to the gamma band as lower frequency oscillations were suppressed consistently across daily nicotine treatments. Gamma oscillations are associated with enhanced attentional capacity. Consistent with this mechanism, the repeat dosing regimen in a separate cohort of subjects led to improved performance in an attention task. These data suggest that procognitive effects of nicotine may involve development of enhanced gamma oscillatory activity and a shift to excitatory-inhibitory balance in PFC neural activity. In the context of the clinical use of nicotine and related agonists for treating cognitive deficits, these data suggest that daily dosing may be critical to allow for development of robust gamma oscillations.
... As discussed, mPFC plays a key role in attention. However, optimal attentional performance requires neuronal synchrony between mPFC and other cortical and subcortical structures [Gregoriou, Paneri, & Sapountzis, 2015;Miller & Buschman, 2013]. Studies on autistic individuals and their siblings suggest reduced gamma synchrony between functionally connected brain regions associated with compromised perceptual functions [Rojas & Wilson, 2014;Uhlhaas & Singer, 2006]. ...
Lay summary:
We studied rats prenatally exposed to valproic acid (VPA), an established rodent model of autism. Both male and female VPA rats had a range of attentional impairments with sex-specific characteristics. Importantly, with fixed rules, graded difficulty levels, and more time, VPA rats could be successfully trained on the attentional task. Our work validates the use of the VPA model in the quest for evaluating suitable therapeutic targets for improving attentional performance.
... We will discuss the implications of these findings with respect to the role of oscillatory entrainment in selective attention, sensoryemotor interactions during rhythmic tasks, and the use of rhythmic stimuli in the rehabilitation of PD patients. Studies have shown that oscillatory activity has an important role in numerous brain functions and processes, and an example of this is the strong influence of oscillatory activity on attentional processing (for review see Gregoriou, Paneri, & Sapountzis, 2015). Neural oscillations are capable of promoting or suppressing the detection of external stimuli (Henry & Obleser, 2012;VanRullen, Busch, Drewes, & Dubois, 2011), as they reflect the excitability of the neural tissue in which they occur (Lakatos et al., 2005;Steriade, McCormick, & Sejnowski, 1993). ...
Neural entrainment plays a crucial role in perception and action, especially when stimuli possess a certain temporal regularity, and is also suggested to serve as a neural process to select and attend the relevant stream in situations where there are competing stimulus streams. Beneficial effects of entrainment have led to the suggestion that rhythmic stimuli can improve motor function in patients with Parkinson's disease (PD). Behavioural studies support this suggestion, but neurophysiological studies have shown reduced entrainment of motor areas in PD. However, oscillatory entrainment in PD has only been tested in paradigms with a single isochronous stimulus stream, whereas entrainment has an enhanced benefit in situations where one rhythmic
stimulus stream has to be segregated from distractor stimuli. Therefore, we here used an intermodal selective attention task with concurrent auditory and visual stimulus streams while recording oscillatory brain activity with MEG. We aimed to (i) replicate earlier findings of deficient motor entrainment in PD patients in conditions where there is a single stimulus stream, and (ii) to evaluate whether increasing the benefit of entrainment by introducing a distractor stream would lead to entrainment in PD patients not seen otherwise. Contrary to this
hypothesis, PD patients showed reduced motor entrainment compared to controls during both conditions, as indexed by beta oscillatory activity. These results suggest that entrainment in PD patients is deficient, even
under conditions that encourage entrainment.
... [29,48] such stimulus-related activity has been associated with the frequency band 10-30 Hz including both alpha and beta frequencies. At the same time, our results, similarly to [49,50], reveal the differences in alpha and beta activity. This represents itself as the difference in the structure of the links in these bands. ...
Stimulus-related brain activity is considered using wavelet-based analysis of neural interactions between occipital and parietal brain areas in alpha (8-12 Hz) and beta (15-30 Hz) frequency bands. We show that human sensory processing related to the visual stimuli perception induces brain response resulted in different ways of parieto-occipital interactions in these bands. In the alpha frequency band the parieto-occipital neuronal network is characterized by homogeneous increase of the interaction between all interconnected areas both within occipital and parietal lobes and between them. In the beta frequency band the occipital lobe starts to play a leading role in the dynamics of the occipital-parietal network: The perception of visual stimuli excites the visual center in the occipital area and then, due to the increase of parieto-occipital interactions, such excitation is transferred to the parietal area, where the attentional center takes place. In the case when stimuli are characterized by a high degree of ambiguity, we find greater increase of the interaction between interconnected areas in the parietal lobe due to the increase of human attention. Based on revealed mechanisms, we describe the complex response of the parieto-occipital brain neuronal network during the perception and primary processing of the visual stimuli. The results can serve as an essential complement to the existing theory of neural aspects of visual stimuli processing.
... Hz). Oscillations within specific frequencies have been linked to particular cells and associated circuits, presumably maximizing the integration of information across neural networks in the context of behavioral demands (Friston, Bastos, Pinotsis, & Litvak, 2014;Gregoriou, Paneri, & Sapountzis, 2015). ...
Resting state functional magnetic resonance imaging studies of psychosis have focused primarily on the amplitude of low‐frequency fluctuations in the blood oxygen level dependent (BOLD) signal ranging from .01 to 0.1 Hz. Few studies, however, have investigated the amplitude of frequency fluctuations within discrete frequency bands and higher than 0.1 Hz in patients with psychosis at different illness stages. We investigated BOLD signal within three frequency ranges including slow‐4 (.027–.073 Hz), slow‐3 (.074–0.198 Hz) and slow‐2 (0.199–0.25 Hz) in 89 patients with either first‐episode or chronic psychosis and 119 healthy volunteers. We investigated the amplitude of frequency fluctuations within three frequency bands using 47 regions‐of‐interest placed within 14 known resting state networks derived using group independent component analysis. There were significant group x frequency interactions for the visual and motor cortex networks, with the largest significant group differences (patients < healthy volunteers) evident in slow‐4 and slow‐3, respectively. Also, healthy volunteers had an overall higher amplitude of frequency fluctuations compared to patients across the three frequency ranges in the visual cortex, dorsal attention and motor cortex networks with the opposite effect (patients > healthy volunteers) evident within the salience and frontal gyrus networks. Subsequent analyses indicated that these effects were evident in both first‐episode and chronic patients. Our study provides new data regarding the importance of BOLD signal fluctuations within different frequency bands in the neurobiology of psychosis.
... Further, spatial and feature attention are both associated with changes in the pairwise correlations between the firing rates of sensory neurons (Cohen and Maunsell, 2009;Mitchell et al., 2009;Verhoef and Maunsell, 2017), and the relationship between modulations of firing rate and of pairwise correlations is quantitatively indistinguishable for spatial versus feature attention (Cohen and Maunsell, 2011). Both forms of attention increase gamma frequency synchronization (for review, see Gregoriou et al., 2015) and, finally, spatial and feature attention may share a common top-down source of attention signals (Moore and Armstrong, 2003;Gregoriou et al., 2009;Zhou and Desimone, 2011; but see Paneri and Gregoriou, 2017). ...
Although spatial and feature attention have differing effects on neuronal responses in visual cortex, it remains unclear why. Response normalization has been implicated in both types of attention (Carandini and Heeger, 2011), and single-unit studies have demonstrated that the magnitude of spatial attention effects on neuronal responses covaries with the magnitude of normalization effects. However, the relationship between feature attention and normalization remains largely unexplored. We recorded from individual neurons in the middle temporal area of rhesus monkeys using a task that allowed us to isolate the effects of feature attention, spatial attention, and normalization on the responses of each neuron.Wefound that the magnitudes of neuronal response modulations due to spatial attention and feature attention are correlated; however, whereas modulations due to spatial attention are correlated with normalization strength, those due to feature attention are not. Additionally, spatial attention modulations are stronger with multiple stimuli in the receptive field, whereas feature attention modulations are not. These findings are captured by a model in which spatial and feature attention share common top-down attention signals that nonetheless result in differing sensory neuron response modulations because of a spatially tuned sensory normalization mechanism. This model explains previously reported commonalities and differences between these two types of attention by clarifying the relationship between top-down attention signals and sensory normalization.Weconclude that similar top-down signals to visual cortex can have distinct effects on neuronal responses due to distinct interactions with sensory mechanisms.
... Fig. 3 demonstrates the types of possible interactions of the EEG rhythms, due to both adjacency of the oscillation frequency ranges (e.g. delta and theta, etc.), but also to the ratios of the bio-potentials power in different frequency ranges: delta/alpha, theta/beta and theta/gamma, alpha/beta or beta/gamma, each of which having its functional specificity [7,13,29,24,25]. In the Fig. 3, the relations between the ontological concepts are as follows: ...
... The blind field showed a modulation of the gamma oscillatory activity that was higher in the valid than in the invalid condition. Some authors (Gregoriou, Paneri, & Sapountzis, 2015;Gruber et al., 1999) have proposed that, during an attentional task, this modulation could be associated with motion perception and an effective integration of inputs. In our experiment we used a flickering stimulus and this could be a crucial feature for unconscious perception in this group of patients enabling them to enhance the response to valid trials, as witnessed behaviorally by the RT attention validity effect in the blind field. ...
The aim of this research was to study the behavioral and neurophysiological correlates of visual attention orientation to unseen stimuli presented to the blind hemifield of hemianopic patients, and the existence of hemispheric differences for this kind of unconscious attention. Behaviorally, by using a Posner paradigm, we found a significant attention effect in speed of response to unseen stimuli similar to that observed in the sighted hemifield and in healthy participants for visible stimuli. Moreover, event-related potential (ERP) and oscillatory attention-related activity were present following stimulus presentation to the blind hemifield. Importantly, in patients this pattern of activity was different as a function of the side of the brain lesion: Left damaged patients showed attention-related ERP and oscillatory activity broadly similar to that found in healthy participants. In contrast, right damaged patients showed a radically different pattern. These data confirm and extend to neurophysiological mechanisms the existence of unconscious visual orienting and are in keeping with a right hemisphere dominance for both unconscious and conscious attention.
... While it remains to be determined how attention engages PV neurons in the auditory system, PV neuron activity in the prefrontal cortex is increased with goal-driven attentional processing and PV neuron activity levels correlated with behavioral performance on the 5-choice serial reaction time task, a common rodent attentional task (Kim et al., 2016). Importantly, PV neurons play in integral role in generation of gamma oscillations in the cortex (Cardin et al., 2009;Sohal et al., 2009) and attentional processing is characterized by increases in gamma activity in sensory regions (Fries et al., 2001;Gregoriou et al., 2015;Ni et al., 2016). Gamma activity has been suggested to modulate the gain of incoming sensory input (Tiesinga et al., 2004(Tiesinga et al., , 2008Börgers et al., 2005;Ni et al., 2016), providing a link between PV neuron function and attentional gain control (Tiesinga et al., 2004(Tiesinga et al., , 2008Börgers et al., 2005;Ni et al., 2016). ...
Listening in noisy or complex sound environments is difficult for individuals with normal hearing and can be a debilitating impairment for those with hearing loss. Extracting meaningful information from a complex acoustic environment requires the ability to accurately encode specific sound features under highly variable listening conditions and segregate distinct sound streams from multiple overlapping sources. The auditory system employs a variety of mechanisms to achieve this auditory scene analysis. First, neurons across levels of the auditory system exhibit compensatory adaptations to their gain and dynamic range in response to prevailing sound stimulus statistics in the environment. These adaptations allow for robust representations of sound features that are to a large degree invariant to the level of background noise. Second, listeners can selectively attend to a desired sound target in an environment with multiple sound sources. This selective auditory attention is another form of sensory gain control, enhancing the representation of an attended sound source while suppressing responses to unattended sounds. This review will examine both “bottom-up” gain alterations in response to changes in environmental sound statistics as well as “top-down” mechanisms that allow for selective extraction of specific sound features in a complex auditory scene. Finally, we will discuss how hearing loss interacts with these gain control mechanisms, and the adaptive and/or maladaptive perceptual consequences of this plasticity.
... Furthermore, we also found that unusual ReHo in NE was linked with slow-5 band, while the results in slow-2 and slow-3 were mainly in white matter and negative in other bands . Oscillatory synchrony in specific frequencies were found to be related to particular cells and associated circuits and enabled the brain to be flexible so as to gear to behavioral demands 53 . Apparently, more studies were required to locate the particular oscillators in NE children's brains. ...
Resting state functional magnetic resonance imaging studies of nocturnal enuresis have focused primarily on regional metrics in the blood oxygen level dependent (BOLD) signal ranging from 0.01 to 0.08 Hz. However, it remains unclear how local metrics show in sub-frequency band. 129 children with nocturnal enuresis (NE) and 37 healthy controls were included in this study. The patients were diagnosed by the pediatricians in Shanghai Children’s Medical Center affiliated to Shanghai Jiao Tong University School of Medicine, according to the criteria from International Children's Continence Society (ICCS). Questionnaires were used to evaluate the symptoms of enuresis and completed by the participants. In this study, fALFF, ReHo and PerAF were calculated within five different frequency bands: typical band (0.01–0.08 Hz), slow-5 (0.01–0.027 Hz), slow-4 (0.027–0.073 Hz), slow-3 (0.073–0.198 Hz), and slow-2 (0.198–0.25 Hz). In the typical band, ReHo increased in the left insula and the right thalamus, while fALFF decreased in the right insula in children with NE. Besides, PerAF was increased in the right middle temporal gyrus in these children. The results regarding ReHo, fALFF and PerAF in the typical band was similar to those in slow-5 band, respectively. A correlation was found between the PerAF value of the right middle temporal gyrus and scores of the urinary intention-related wakefulness. Results in other bands were either negative or in white matter. NE children might have abnormal intrinsic neural oscillations mainly on slow-5 bands.
... Gamma activity has been associated with attention mechanisms. During attention tasks, gamma activity behaves opposite to alpha rhythms, as gamma power is enhanced in task-relevant areas [37]. Gamma activity is proposed to reflect feed-forward, bottom-up processes, contrary to alpha rhythms which are more closely associated with feedback, top-down mechanisms [32,80]. ...
A bstract
There is growing evidence that migraine is associated with attentional abnormalities, both during and outside migraine attacks, which would impact the cognitive processing of sensory stimulation. However, these attention alterations are poorly characterized and their neurophysiological basis is still unclear. Nineteen migraineurs without aura and nineteen healthy participants were recruited to perform a task which used visually-cued auditory targets and distracting sounds to evaluate conjointly top-down and bottom-up attention mechanisms. Magnetoencephalography (MEG) signals were recorded. We investigated anticipatory alpha activity (power increase and decrease) and distractor-induced gamma activity as markers for top-down (inhibition and facilitation) and bottom-up attention, respectively. Compared to healthy participants, migraineurs presented a significantly less prominent alpha power increase in visual areas in anticipation of the auditory target, indexing a reduced inhibition of task-irrelevant visual areas. However, there was no significant group difference regarding the alpha power decrease in the relevant auditory cortices in anticipation of the target, nor regarding the distractor-induced gamma power increase in the ventral attention network. These results in the alpha band suggest that top-down inhibitory processes in the visual cortices are deficient in migraine but there is no clear evidence supporting a disruption of top-down facilitatory attentional processes. This relative inability to suppress irrelevant sensory information may be underlying the self-reported increased distractibility and contribute to sensory disturbances in migraine.
... Another important effect of attention is a decrease in the correlated variability of visual neurons, which might be an even more significant factor with respect to general reductions in SNR than the modulation of firing rates (Cohen and Maunsell, 2009;Mitchell et al., 2009;Deco and Hugues, 2012;Paneri and Gregoriou, 2017). Additionally, attention might lead to frequency specific modulations of local oscillatory activity at different stages of visual processing (Gregoriou et al., 2015). These modulations include rhythmic synchronizations in the gamma band range (30-60 Hz) which might result in a more effective processing (Murthy and Fetz, 1994;Fries, 2005Fries, , 2009Deco and Thiele, 2009;van Es and Schoffelen, 2019). ...
Visual attention is the cognitive process that mediates the selection of important information from the environment. This selection is usually controlled by bottom-up and top-down attentional biasing. Since for most humans vision is the dominant sense, visual attention is critically important for higher-order cognitive functions and related deficits are a core symptom of many neuropsychiatric and neurological disorders. Here, we summarize the importance and relative contributions of different neuromodulators and neurotransmitters to the neural mechanisms of top-down and bottom-up attentional control. We will not only review the roles of widely accepted neuromodulators, such as acetylcholine, dopamine and noradrenaline, but also the contributions of other modulatory substances. In doing so, we hope to shed some light on the current understanding of the role of neurochemistry in shaping neuron properties contributing to the allocation of attention in the visual field.
... By obtaining EEG or LFP measurements, while humans or animals transition between different brain states, we now have a very well-defined characterization of how distinct neuronal oscillations change as a function of state. For example, the shift from sleep to awake is associated with a marked suppression of delta oscillations (Berger, 1931;Harris and Thiele, 2011;Kryger et al., 2017;Lee and Dan, 2012;Steriade et al., 2001), while gamma oscillations are prominently enhanced when animals transition from quiet to active wakefulness (Crochet and Petersen, 2006;Harris and Thiele, 2011;McGinley et al., 2015b;Poulet and Crochet, 2019;Poulet and Petersen, 2008), or during attentional processing (Gregoriou et al., 2015(Gregoriou et al., , 2014(Gregoriou et al., , 2009. Neuronal oscillations emerge from the concerted activity of ensembles of neurons, and numerous studies have established a strong link between such oscillations and the activity of individual neurons. ...
Throughout the nervous system, ion gradients drive fundamental processes. Yet, the roles of interstitial ions in brain functioning is largely forgotten. Emerging literature is now revitalizing this area of neuroscience by showing that interstitial cations (K⁺, Ca²⁺ and Mg²⁺) are not static quantities but change dynamically across states such as sleep and locomotion. In turn, these state-dependent changes are capable of sculpting neuronal activity; for example, changing the local interstitial ion composition in the cortex is sufficient for modulating the prevalence of slow-frequency neuronal oscillations, or potentiating the gain of visually evoked responses. Disturbances in interstitial ionic homeostasis may also play a central role in the pathogenesis of central nervous system diseases. For example, impairments in K⁺ buffering occur in a number of neurodegenerative diseases, and abnormalities in neuronal activity in disease models disappear when interstitial K⁺ is normalized. Here we provide an overview of the roles of interstitial ions in physiology and pathology. We propose the brain uses interstitial ion signaling as a global mechanism to coordinate its complex activity patterns, and ion homeostasis failure contributes to central nervous system diseases affecting cognitive functions and behavior.
... Alpha waves (8-13 Hz), sourced in frontal sites including the anterior cingulate cortex, have been shown to be related to attention and WM, and importantly, to suppression of unattended stimuli (Handel et al., 2011). Finally, beta waves show involvement in spatial attention processes, although their exact role in cognition is less clear (see recent review in Gregoriou et al., 2015). ...
This chapter highlights the key role of two main factors, attentional control and reward processing, in unlocking brain plasticity. We first review the evidence for the role that each of these mechanisms plays in neuroplasticity, and then make the case that tools and technologies that combine these two are likely to result in maximal and broad, generalized benefits. In this context, we review the evidence concerning the impact of video game play on brain plasticity, with an eye toward plasticity-driving methods such as the seamless integration of neurofeedback into the video game platforms.
... Consequently, the signal-to-noise ratio improves (Cohen and Maunsell, 2009;Mitchell et al., 2009). Moreover, top-down attention modulates local oscillatory activity of primary sensory cortices in a frequency-specific manner (Gregoriou et al., 2015). For example, during attentional selection, neurons in visual and frontal areas encoding the attended location or feature synchronize their activity in gamma frequency (30-60 Hz) range (Tallon-Baudry et al., 2004;Bichot et al., 2005;Fries, 2005;Kreiter et al., 2005;Fries et al., 2008;Gregoriou et al., 2009). ...
The emergence of cross-modal learning capabilities requires the interaction of neural areas accounting for sensory and cognitive processing. Convergence of multiple sensory inputs is observed in low-level sensory cortices including primary somatosensory (S1), visual (V1), and auditory cortex (A1), as well as in high-level areas such as prefrontal cortex (PFC). Evidence shows that local neural activity and functional connectivity between sensory cortices participate in cross-modal processing. However, little is known about the functional interplay between neural areas underlying sensory and cognitive processing required for cross-modal learning capabilities across life. Here we review our current knowledge on the interdependence of low- and high-level cortices for the emergence of cross-modal processing in rodents. First, we summarize the mechanisms underlying the integration of multiple senses and how cross-modal processing in primary sensory cortices might be modified by top-down modulation of the PFC. Second, we examine the critical factors and developmental mechanisms that account for the interaction between neuronal networks involved in sensory and cognitive processing. Finally, we discuss the applicability and relevance of cross-modal processing for brain-inspired intelligent robotics. An in-depth understanding of the factors and mechanisms controlling cross-modal processing might inspire the refinement of robotic systems by better mimicking neural computations.
... In general, however, oscillation implies a capacity for information maintenance (Buzsáki and Draguhn, 2004). This may be important for maintaining attention and working memory, among other functions (Buzsáki and Draguhn, 2004;Hipp et al., 2011;Aru et al., 2015;Fries, 2015;Gregoriou et al., 2015;Gupta and Chen, 2016). Instantaneous coupling of signals ("microstates") are another variation on the communicative role of oscillations (Schack, 2004;Dimitriadis et al., 2013). ...
Space generally overshadows time in the construction of theories in cognitive neuroscience. In this paper, we pivot from the spatial axes to the temporal, analyzing fMRI image series to reveal structures in time rather than space. To determine affinities among global brain patterns at different times, core concepts in network analysis (derived from graph theory) were applied temporally, as relations among brain images at every time point during an fMRI scanning epoch. To explore the temporal structures observed through this adaptation of network analysis, data from 180 subjects in the Human Connectome Project were examined, during two experimental conditions: passive movie viewing and rest. The temporal brain, like the spatial brain, exhibits a modular structure, where “modules” are intermittent (distributed in time). These temporal entities are here referred to as themes. Short sequences of themes – motifs – were studied in sequences from 4 to 11 s in length. Many motifs repeated at constant intervals, and are therefore rhythmic; rhythms, converted to frequencies, were often harmonic. We speculate that the structure and interaction of these global oscillations underwrites the capacity to experience and navigate a world which is both recognizably stable and noticeably changing at every moment – a temporal world. In its temporal structure, this brain-constituted world resembles music.
Attention refers to the set of ever‐present functions that prioritize and select information to guide adaptive behavior. As such, it is fundamental to almost all aspects of cognition. In this chapter, we review the psychological and neuroscientific literatures concerned with understanding its principles and mechanisms. We chart the scientific advances that have brought us to the appreciation that all levels of information processing are continuously, proactively, and dynamically modulated according to our goals, motivations, and memories.
Time is a critical component of episodic memory. Yet it is currently unclear how different types of temporal signals are represented in the brain and how these temporal signals support episodic memory. The current study investigated whether temporal cues provided by low-frequency environmental rhythms influence memory formation. Specifically, we tested the hypothesis that neural tracking of low-frequency rhythm serves as a mechanism of selective attention that dynamically biases the encoding of visual information at specific moments in time. Participants incidentally encoded a series of visual objects while passively listening to background, instrumental music with a steady beat. Objects either appeared in-synchrony or out-of-synchrony with the background beat. Participants were then given a surprise subsequent memory test (in silence). Results revealed significant neural tracking of the musical beat at encoding, evident in increased electrophysiological power and inter-trial phase coherence at the perceived beat frequency (1.25 Hz). Importantly, enhanced neural tracking of the background rhythm at encoding was associated with superior subsequent memory for in-synchrony compared to out-of-synchrony objects at test. Together, these results provide novel evidence that the brain spontaneously tracks low-frequency musical rhythm during naturalistic listening situations, and that the strength of this neural tracking is associated with the effects of rhythm on higher-order cognitive processes such as episodic memory.
Selective attention plays a key role in determining what aspects of our environment are encoded into long-term memory. Auditory rhythms with a regular beat provide temporal expectations that entrain attention and facilitate perception of visual stimuli aligned with the beat. The current study investigated whether entrainment to background auditory rhythms also facilitates higher-level cognitive functions such as episodic memory. In a series of experiments, we manipulated temporal attention through the use of rhythmic, instrumental music. In Experiment 1A and 1B, we found that background musical rhythm influenced the encoding of visual targets into memory, evident in enhanced subsequent memory for targets that appeared in-synchrony compared to out-of-synchrony with the background beat. Response times at encoding did not differ for in-synchrony compared to out-of-synchrony stimuli, suggesting that the rhythmic modulation of memory does not simply reflect rhythmic effects on perception and action. Experiment 2 investigated whether rhythmic effects on response times emerge when task procedures more closely match prior studies that have demonstrated significant auditory entrainment effects. Responses were faster for in-synchrony compared to out-of-synchrony stimuli when participants performed a more perceptually-oriented task that did not contain intervening recognition memory tests, suggesting that rhythmic effects on perception and action depend on the nature of the task demands. Together, these results support the hypothesis that rhythmic temporal regularities provided by background music can entrain attention and influence the encoding of visual stimuli into memory.
Studies manipulating neural activity acutely with optogenetic or chemogenetic intervention in behaving rodents have increased considerably in recent years. More often, these circuit-level neural manipulations are tested within an existing framework of behavioural testing that strives to model complex executive functions or symptomologies relevant to multidimensional psychiatric disorders in humans, such as attentional control deficits, impulsivity or behavioural (in)flexibility. This methods perspective argues in favour of carefully implementing these acute circuit-based approaches to better understand and model cognitive symptomologies or their similar isomorphic animal behaviours, which often arise and persist in overlapping brain circuitries. First, we offer some practical considerations for combining long-term, behavioural paradigms with optogenetic or chemogenetic interventions. Next, we examine how cell-type or projection-specific manipulations to the ascending neuromodulatory systems, local brain region or descending cortical glutamatergic projections influence aspects of cognitive control. For this, we primarily focus on the influence exerted on attentional and motor impulsivity performance in the (3-choice or) 5-choice serial reaction time task, and impulsive, risky or inflexible choice biases during alternative preference, reward discounting or reversal learning tasks.
How does the brain implement cognitive processes? Part of the answer is specialization of function in particular regions. But complex cognitive processes involved in attention, memory, and consciousness require the coordinated activity of several or many of these specialized regions. Moreover, the specialized regions often (always?) exhibit different functions depending on the particular subset of other regions with which they are interacting. Finally, because cognitive tasks vary dramatically over timescales of hundreds of milliseconds to seconds, the functionally relevant regional networks must form and dissolve over these short timescales, which are too short to accommodate mechanisms such as synaptic modification via spike-timing dependent plasticity. It has been suggested that oscillatory synchronization of neural activity provides a mechanism whereby networks of functionally specialized brain regions could function transiently on such timescales. This chapter begins to make the case that for attention and consciousness, at least, this mechanism is deeply involved in implementing the required functional networks. It also briefly considers the implications of the role of oscillatory neural synchronization in cognition for the global workspace.
This chapter describes using wavelet analysis to study mechanisms of visual perception. First, we introduce an ambiguous visual stimulus, the Necker cube, a useful visual perception analysis tool. Second, we demonstrate how the wavelet-based methods reveal the local and network properties of the percept-related brain activity. Then, we considered the effect of the human condition (motivation and alertness) on the perceptive process. Finally, we review the basic principles of the brain-computer interfaces that use the wavelet-based algorithm to evaluate the human state in visual perception tasks.
As we move in the environment, attention shifts to novel objects of interest based on either their sensory salience or behavioral value (reorienting). This study measures with magnetoencephalography (MEG) different properties (amplitude, onset-to-peak duration) of event-related desynchronization/synchronization (ERD/ERS) of oscillatory activity during a visuospatial attention task designed to separate activity related to reorienting vs. maintaining attention to the same location, controlling for target detection and response processes. The oscillatory activity was measured both in fMRI-defined regions of the interest (ROIs) of the dorsal attention (DAN) and visual (VIS) networks, previously defined as task-relevant in the same subjects, or whole-brain in a pre-defined set of cortical ROIs encompassing the main brain networks.
Reorienting attention (shift cues) as compared to maintaining attention (stay cues) produced a temporal sequence of ERD/ERS modulations at multiple frequencies in specific anatomical regions/networks. An early (∼330 ms), stronger, transient theta ERS occurred in task-relevant (DAN, VIS) and control networks (VAN, CON, FPN), possibly reflecting an alert/reset signal in response to the cue. A more sustained, behaviorally relevant, low-beta band ERD peaking ∼450 ms following shift cues (∼410 for stay cues) localized in frontal and parietal regions of the DAN. This modulation is consistent with a control signal re-routing information across visual hemifields. Contralateral vs. ipsilateral shift cues produced in occipital visual regions, a stronger, sustained alpha ERD (peak ∼470 ms) and a longer, transient high beta/gamma ERS (peak ∼490 ms) related to preparatory visual modulations in advance of target occurrence.
This is the first description of a cascade of oscillatory processes during attentional reorienting in specific anatomical regions and networks. Among these processes, a behaviorally relevant beta desynchronization in the FEF is likely associated with the control of attention shifts.
While signatures of attention have been extensively studied in sensory systems, the neural sources and computations responsible for top-down control of attention are largely unknown. Using chronic recordings in mice, we found that fast-spiking parvalbumin (FS-PV) interneurons in medial prefrontal cortex (mPFC) uniformly show increased and sustained firing during goal-driven attentional processing, correlating to the level of attention. Elevated activity of FS-PV neurons on the timescale of seconds predicted successful execution of behavior. Successful allocation of attention was characterized by strong synchronization of FS-PV neurons, increased gamma oscillations, and phase locking of pyramidal firing. Phase-locked pyramidal neurons showed gamma-phase-dependent rate modulation during successful attentional processing. Optogenetic silencing of FS-PV neurons deteriorated attentional processing, while optogenetic synchronization of FS-PV neurons at gamma frequencies had pro-cognitive effects and improved goal-directed behavior. FS-PV neurons thus act as a functional unit coordinating the activity in the local mPFC circuit during goal-driven attentional processing.
This article proposes what we call an “EEG-Copeia” for neurofeedback, like the “Pharmacopeia” for psychopharmacology. This paper proposes to define an “EEG-Copeia” as an organized list of scientifically validated EEG markers, characterized by a specific association with an identified cognitive process, that define a psychophysiological unit of analysis useful for mental or brain disorder evaluation and treatment. A characteristic of EEG neurofeedback for mental and brain disorders is that it targets a EEG markers related to a supposed cognitive process, whereas conventional treatments target clinical manifestations. This could explain why EEG neurofeedback studies encounter difficulty in achieving reproducibility and validation. The present paper suggests that a first step to optimize EEG neurofeedback protocols and future research is to target a valid EEG marker. The specificity of the cognitive skills trained and learned during real time feedback of the EEG marker could be enhanced and both the reliability of neurofeedback training and the therapeutic impact optimized. However, several of the most well-known EEG markers have seldom been applied for neurofeedback. Moreover, we lack a reliable and valid EEG targets library for further RCT to evaluate the efficacy of neurofeedback in mental and brain disorders. With the present manuscript, our aim is to foster dialogues between cognitive neuroscience and EEG neurofeedback according to a psychophysiological perspective. The primary objective of this review was to identify the most robust EEG target. EEG markers linked with one or several clearly identified cognitive-related processes will be identified. The secondary objective was to organize these EEG markers and related cognitive process in a psychophysiological unit of analysis matrix inspired by the Research Domain Criteria (RDoC) project.
Prediction and attention are fundamental brain functions in the service of perception and action. Theories on prediction relate to neural (mental) models inferring about (present or future) sensory or action-related information, whereas theories of attention relate to the control of information flow underlying perception and action. Both concepts are related and not always clearly distinguishable. The special issue includes current research on prediction and attention in various subfields of perception and action. It especially considers interactions between predictive and attentive processes, which constitute a newly emerging and highly interesting field of research. As outlined in this editorial, the contributions in this special issue allow specifying as well as bridging concepts on prediction and attention. The joint consideration of prediction and attention also reveals common functional principles of perception and action.
Gamma oscillations are a prominent feature of various neural systems, including the CA3 subfield of the hippocampus. In CA3, in vitro carbachol application induces ∼40 Hz gamma oscillations in the network of glutamatergic excitatory pyramidal neurons (PNs) and local GABAergic inhibitory neurons (INs). Activation of NMDA receptors within CA3 leads to an increase in the frequency of carbachol-induced oscillations to ∼60 Hz, a broadening of the distribution of individual oscillation cycle frequencies, and a decrease in the time lag between PN and IN spike bursts. In this work, we develop a biophysical integrate-and-fire model of the CA3 subfield, we show that the dynamics of our model are in concordance with physiological observations, and we provide computational support for the hypothesis that the ‘E-I’ mechanism is responsible for the emergence of ∼40 Hz gamma oscillations in the absence of NMDA activation. We then incorporate NMDA receptors into our CA3 model, and we show that our model exhibits the increase in gamma oscillation frequency, broadening of the cycle frequency distribution, and decrease in the time lag between PN and IN spike bursts observed experimentally. Remarkably, we find an inverse relationship in our model between the net NMDA current delivered to PNs and INs in an oscillation cycle and cycle frequency. Furthermore, we find a disparate effect of NMDA receptors on PNs versus INs – we show that NMDA receptors on INs tend to increase oscillation frequency, while NMDA receptors on PNs tend to slightly decrease or not affect oscillation frequency. We find that these observations can be explained if NMDA activity above a threshold level causes a shift in the mechanism underlying gamma oscillations; in the absence of NMDA receptors, the ‘E-I’ mechanism is primarily responsible for the generation of gamma oscillations (at 40 Hz), while when NMDA receptors are active, the mechanism of gamma oscillations shifts to the ‘I-I’ mechanism, and we argue that within the ‘I-I’ regime (which displays a higher baseline oscillation frequency of ∼60 Hz), slight changes in the level of NMDA activity are inversely related to cycle frequency.
The communication-through-coherence (CTC) hypothesis proposes that anatomical connections are dynamically rendered effective or ineffective through the presence or absence of rhythmic synchronization, in particular in the gamma and beta bands. The original CTC statement proposed that uni-directional communication is due to rhythmic entrainment with an inter-areal delay and a resulting non-zero phase relation, whereas bi-directional communication is due to zero-phase synchronization. Recent studies found that inter-areal gamma-band synchronization entails a non-zero phase lag. We therefore modify the CTC hypothesis and propose that bi-directional cortical communication is realized separately for the two directions by uni-directional CTC mechanisms entailing delays in both directions. We review evidence suggesting that inter-areal influences in the feedforward and feedback directions are segregated both anatomically and spectrally.
Cognitive functions rely on the coordinated activity of neurons in many brain regions, but the interactions between cortical areas are not yet well understood. Here we investigated whether low-frequency (α) and high-frequency (γ) oscillations characterize different directions of information flow in monkey visual cortex. We recorded from all layers of the primary visual cortex (V1) and found that γ-waves are initiated in input layer 4 and propagate to the deep and superficial layers of cortex, whereas α-waves propagate in the opposite direction. Simultaneous recordings from V1 and downstream area V4 confirmed that γ- and α-waves propagate in the feedforward and feedback direction, respectively. Microstimulation in V1 elicited γ-oscillations in V4, whereas microstimulation in V4 elicited α-oscillations in V1, thus providing causal evidence for the opposite propagation of these rhythms. Furthermore, blocking NMDA receptors, thought to be involved in feedback processing, suppressed α while boosting γ. These results provide new insights into the relation between brain rhythms and cognition.
We tested the sensory impact of repeated synchronization of fast-spiking interneurons (FS), an activity pattern thought to underlie neocortical gamma oscillations. We optogenetically drove 'FS-gamma' while mice detected naturalistic vibrissal stimuli and found enhanced detection of less salient stimuli and impaired detection of more salient ones. Prior studies have predicted that the benefit of FS-gamma is generated when sensory neocortical excitation arrives in a specific temporal window 20-25 ms after FS synchronization. To systematically test this prediction, we aligned periodic tactile and optogenetic stimulation. We found that the detection of less salient stimuli was improved only when peripheral drive led to the arrival of excitation 20-25 ms after synchronization and that other temporal alignments either had no effects or impaired detection. These results provide causal evidence that FS-gamma can enhance processing of less salient stimuli, those that benefit from the allocation of attention.
When a sensory stimulus repeats, neuronal firing rate and functional MRI blood oxygen level-dependent responses typically decline, yet perception and behavioral performance either stay constant or improve. An additional aspect of neuronal activity is neuronal synchronization, which can enhance the impact of neurons onto their postsynaptic targets independent of neuronal firing rates. We show that stimulus repetition leads to profound changes of neuronal gamma-band (∼40–90 Hz) synchronization. Electrocorticographic recordings in two awake macaque monkeys demonstrated that repeated presentations of a visual grating stimulus resulted in a steady increase of visually induced gamma-band activity in area V1, gamma-band synchronization between areas V1 and V4, and gamma-band activity in area V4. Microelectrode recordings in area V4 of two additional monkeys under the same stimulation conditions allowed a direct comparison of firing rates and gamma-band synchronization strengths for multiunit activity (MUA), as well as for isolated single units, sorted into putative pyramidal cells and putative interneurons. MUA and putative interneurons showed repetition-related decreases in firing rate, yet increases in gamma-band synchronization. Putative pyramidal cells showed no repetition-related firing rate change, but a decrease in gamma-band synchronization for weakly stimulus-driven units and constant gamma-band synchronization for strongly driven units. We propose that the repetition-related changes in gamma-band synchronization maintain the interareal stimulus signaling and sharpen the stimulus representation by gamma-synchronized pyramidal cell spikes.
Brain circuitry processes information by rapidly and selectively engaging functional neuronal networks. The dynamic formation of networks is often evident in rhythmically synchronized neuronal activity and tightly correlates with perceptual, cognitive and motor performances. But how synchronized neuronal activity contributes to network formation and how it relates to the computation of behaviorally relevant information has remained difficult to discern. Here we structure recent empirical advances that link synchronized activity to the activation of so-called dynamic circuit motifs. These motifs explicitly relate (1) synaptic and cellular properties of circuits to (2) identified timescales of rhythmic activation and to (3) canonical circuit computations implemented by rhythmically synchronized circuits. We survey the ubiquitous evidence of specific cell and circuit properties underlying synchronized activity across theta, alpha, beta and gamma frequency bands and show that their activation likely implements gain control, context-dependent gating and state-specific integration of synaptic inputs. This evidence gives rise to the dynamic circuit motifs hypothesis of synchronized activation states, with its core assertion that activation states are linked to uniquely identifiable local circuit structures that are recruited during the formation of functional networks to perform specific computational operations.
Cognitive control requires the selection and maintenance of task-relevant stimulus–response associations, or rules. The dorsolateral
prefrontal cortex (DLPFC) has been implicated by lesion, functional imaging, and neurophysiological studies to be involved
in encoding rules, but the mechanisms by which it modulates other brain areas are poorly understood. Here, the functional
relationship of the DLPFC with the superior colliculus (SC) was investigated by bilaterally deactivating the DLPFC while recording
local field potentials (LFPs) in the SC in monkeys performing an interleaved pro- and antisaccade task. Event-related LFPs
showed differences between pro- and antisaccades and responded prominently to stimulus presentation. LFP power after stimulus
onset was higher for correct saccades than erroneous saccades. Deactivation of the DLPFC did not affect stimulus onset related
LFP activity, but reduced high beta (20–30 Hz) and high gamma (60–150 Hz) power during the preparatory period for both pro-
and antisaccades. Spike rate during the preparatory period was positively correlated with gamma power and this relationship
was attenuated by DLPFC deactivation. These results suggest that top-down control of the SC by the DLPFC may be mediated by
beta oscillations.
The voluntary, top-down allocation of visual spatial attention has been linked to changes in the alpha-band of the EEG signal measured over occipital and parietal lobes. In the present study, we investigated how occipitoparietal alpha-band activity changes when people allocate their attentional resources in a graded fashion across the visual field. We asked participants to either completely shift their attention into one hemifield, to balance their attention equally across the entire visual field, or to attribute more attention to one half of the visual field than to the other. As expected, we found that alpha-band amplitudes decreased stronger contralaterally than ipsilaterally to the attended side when attention was shifted completely. Alpha-band amplitudes decreased bilaterally when attention was balanced equally across the visual field. However, when participants allocated more attentional resources to one half of the visual field, this was not reflected in the alpha-band amplitudes, which just decreased bilaterally. We found that the performance of the participants was more strongly reflected in the coherence between frontal and occipitoparietal brain regions. We conclude that low alpha-band amplitudes seem to be necessary for stimulus detection. Further, complete shifts of attention are directly reflected in the lateralization of alpha-band amplitudes. In the present study, a gradual allocation of visual attention across the visual field was only indirectly reflected in the alpha-band activity over occipital and parietal cortices.
It is widely held that the frontal eye field (FEF) in prefrontal cortex (PFC) modulates processing in visual cortex with attention, although the evidence that it is necessary is equivocal. To help identify critical sources of attentional feedback to area V4, we surgically removed the entire lateral PFC, including the FEF, in one hemisphere and transected the corpus callosum and anterior commissure in two macaques. This deprived V4 of PFC input in one hemisphere while keeping the other hemisphere intact. In the absence of PFC, attentional effects on neuronal responses and synchrony in V4 were substantially reduced and the remaining effects of attention were delayed in time, indicating a critical role for PFC. Conversely, distracters captured attention and influenced V4 responses. However, because the effects of attention in V4 were not eliminated by PFC lesions, other sources of top-down attentional control signals to visual cortex must exist outside of PFC.
Sensory systems must rely on powerful mechanisms for organizing complex information. We propose a framework in which inhibitory alpha oscillations limit and prioritize neuronal processing. At oscillatory peaks, inhibition prevents neuronal firing. As the inhibition ramps down within a cycle, a set of neuronal representations will activate sequentially according to their respective excitability. Both top-down and bottom-up drives determine excitability; in particular, spatial attention is a major top-down influence. On a shorter time scale, fast recurrent inhibition segments representations in slots 10-30ms apart, generating gamma-band activity at the population level. The proposed mechanism serves to convert spatially distributed representations in early visual regions to a temporal phase code: that is, 'to-do lists' that can be processed sequentially by downstream regions.
How we attend to objects and their features that cannot be separated by location is not understood. We presented two temporally
and spatially overlapping streams of objects, faces versus houses, and used magnetoencephalography and functional magnetic
resonance imaging to separate neuronal responses to attended and unattended objects. Attention to faces versus houses enhanced
the sensory responses in the fusiform face area (FFA) and parahippocampal place area (PPA), respectively. The increases in
sensory responses were accompanied by induced gamma synchrony between the inferior frontal junction, IFJ, and either FFA or
PPA, depending on which object was attended. The IFJ appeared to be the driver of the synchrony, as gamma phases were advanced
by 20 ms in IFJ compared to FFA or PPA. Thus, the IFJ may direct the flow of visual processing during object-based attention,
at least in part through coupled oscillations with specialized areas such as FFA and PPA.
Background
In the mammalian neocortex, cells that express parvalbumin (PV neurons) comprise a dominant class of inhibitory neuron that substantially overlaps with the fast/narrow-spiking physiological phenotype. Attention has pronounced effects on narrow-spiking neurons in the extrastriate cortex of macaques, and more consistently so than on their broad-spiking neighbors. Cortical neuromodulation by acetylcholine (ACh) is a candidate mechanism for aspects of attention and in the primary visual cortex (V1) of the macaque, receptors for ACh (AChRs) are strongly expressed by inhibitory neurons. In particular, most PV neurons in macaque V1 express m1 muscarinic AChRs and exogenously applied ACh can cause the release of γ-aminobutyric acid. In contrast, few PV neurons in rat V1 express m1 AChRs. While this could be a species difference, it has also been argued that macaque V1 is anatomically unique when compared with other cortical areas in macaques.AimsThe aim of this study was to better understand the extent to which V1 offers a suitable model circuit for cholinergic anatomy in the macaque occipital lobe, and to explore cholinergic modulation as a biological basis for the changes in circuit behavior seen with attention.Materials and methodsWe compared expression of m1 AChRs by PV neurons between area V1 and the middle temporal visual area (MT) in macaque monkeys using dual-immunofluorescence confocal microscopy.Results and conclusionWe find that, as in V1, most PV neurons in MT express m1 AChRs but, unlike in V1, it appears that so do most excitatory neurons. This provides support for V1 as a model of cholinergic modulation of inhibition in macaque visual cortex, but not of cholinergic modulation of visual cortical circuits in general. We also propose that ACh acting via m1 AChRs is a candidate underlying mechanism for the strong effects of attention on narrow-spiking neurons observed in behaving animals.
When a sensory stimulus repeats, neuronal firing rate and functional MRI blood oxygen level-dependent responses typically decline, yet perception and behavioral performance either stay constant or improve. An additional aspect of neuronal activity is neuronal synchronization, which can enhance the impact of neurons onto their postsynaptic targets independent of neuronal firing rates. We show that stimulus repetition leads to profound changes of neuronal gamma-band (∼40-90 Hz) synchronization. Electrocorticographic recordings in two awake macaque monkeys demonstrated that repeated presentations of a visual grating stimulus resulted in a steady increase of visually induced gamma-band activity in area V1, gamma-band synchronization between areas V1 and V4, and gamma-band activity in area V4. Microelectrode recordings in area V4 of two additional monkeys under the same stimulation conditions allowed a direct comparison of firing rates and gamma-band synchronization strengths for multiunit activity (MUA), as well as for isolated single units, sorted into putative pyramidal cells and putative interneurons. MUA and putative interneurons showed repetition-related decreases in firing rate, yet increases in gamma-band synchronization. Putative pyramidal cells showed no repetition-related firing rate change, but a decrease in gamma-band synchronization for weakly stimulus-driven units and constant gamma-band synchronization for strongly driven units. We propose that the repetition-related changes in gamma-band synchronization maintain the interareal stimulus signaling and sharpen the stimulus representation by gamma-synchronized pyramidal cell spikes.
Neuronal rhythms are ubiquitous features of brain dynamics, and are highly correlated with cognitive processing. However, the relationship between the physiological mechanisms producing these rhythms and the functions associated with the rhythms remains mysterious. This article investigates the contributions of rhythms to basic cognitive computations (such as filtering signals by coherence and/or frequency) and to major cognitive functions (such as attention and multi-modal coordination). We offer support to the premise that the physiology underlying brain rhythms plays an essential role in how these rhythms facilitate some cognitive operations.
The basal forebrain provides the primary source of cholinergic input to the cortex, and it has a crucial function in promoting wakefulness and arousal. However, whether rapid changes in basal forebrain neuron spiking in awake animals can dynamically influence sensory perception is unclear. Here we show that basal forebrain cholinergic neurons rapidly regulate cortical activity and visual perception in awake, behaving mice. Optogenetic activation of the cholinergic neurons or their V1 axon terminals improved performance of a visual discrimination task on a trial-by-trial basis. In V1, basal forebrain activation enhanced visual responses and desynchronized neuronal spiking; these changes could partly account for the behavioral improvement. Conversely, optogenetic basal forebrain inactivation decreased behavioral performance, synchronized cortical activity and impaired visual responses, indicating the importance of cholinergic activity in normal visual processing. These results underscore the causal role of basal forebrain cholinergic neurons in fast, bidirectional modulation of cortical processing and sensory perception.
The laminar location of the cell bodies and terminals of interareal connections determines the hierarchical structural organization of the cortex and has been intensively studied. However, we still have only a rudimentary understanding of the connectional principles of feedforward (FF) and feedback (FB) pathways. Quantitative analysis of retrograde tracers was used to extend the notion that the laminar distribution of neurons interconnecting visual areas provides an index of hierarchical distance (percentage of supragranular labeled neurons [SLN]). We show that: 1) SLN values constrain models of cortical hierarchy, revealing previously unsuspected areal relations; 2) SLN reflects the operation of a combinatorial distance rule acting differentially on sets of connections between areas; 3) Supragranular layers contain highly segregated bottom-up and top-down streams, both of which exhibit point-to-point connectivity. This contrasts with the infragranular layers, which contain diffuse bottom-up and top-down streams; 4) Cell filling of the parent neurons of FF and FB pathways provides further evidence of compartmentalization; 5) FF pathways have higher weights, cross fewer hierarchical levels, and are less numerous than FB pathways. Taken together, the present results suggest that cortical hierarchies are built from supra- and infragranular counterstreams. This compartmentalized dual counterstream organization allows point-to-point connectivity in both bottom-up and top-down directions. J. Comp. Neurol. 522:225-259, 2014. (c) 2013 Wiley Periodicals, Inc.
Author Summary
Top-down signals originate from higher cognitive areas such as parietal and prefrontal cortex and propagate to earlier stages of the brain. They have been thought to be associated with selective attention, and recent physiological studies suggest that top-down signals in the beta frequency band can support selective attention. In this study, we employ a computational model to investigate potential mechanisms by which top-down beta rhythms can influence neural responses induced by presentation of stimuli. The model includes several cell types, reportedly crucial for generating cortical rhythmic activity in the gamma and beta frequency bands, and the simulation results show that top-down beta rhythms are capable of reproducing experimentally observed attentional effects on neural responses to visual stimuli. These modulatory effects of top-down beta rhythms are mainly induced via activation of ascending inhibition originating from deep layer slow inhibitory interneurons. Since the excitability of slow interneurons can be increased by cholinergic neuromodulators, these interneurons may mediate the effects of cholinergic tone on attention.
Activation of the cholinergic neurons in the basal forebrain (BF) desynchronizes cortical activity and enhances sensory processing during arousal and attention. How the cholinergic input modulates the activity of different subtypes of cortical neurons remains unclear. Using in vivo two-photon calcium imaging of neurons in layers 1 and 2/3 of mouse visual cortex, we show that electrical stimulation of the BF bi-directionally modulates the activity of excitatory neurons as well as several subtypes of inhibitory interneurons. While glutamatergic activity contributed to the activation of both excitatory and inhibitory neurons, the contribution of acetylcholine (ACh) was more complex. Excitatory and parvalbumin-positive (PV+) neurons were activated through muscarinic ACh receptors (mAChRs) at low levels of cortical desynchronization and suppressed through nicotinic ACh receptors (nAChRs) when cortical desynchronization was strong. In contrast, vasoactive intestinal peptide-positive (VIP+) and layer 1 interneurons were preferentially activated through nAChRs during strong cortical desynchronization. Thus, cholinergic input from the BF causes a significant shift in the relative activity levels of different subtypes of cortical neurons at increasing levels of cortical desynchronization.
Many experiments in neuroscience have compared the strength of association between neural spike trains and rhythms present in local field potential (LFP) recordings. The measure employed in these comparisons, “spike-field coherence”, is a frequency dependent measure of linear association, and is shown to depend on overall neural activity (Lepage et al., 2011). Dependence upon overall neural activity, that is, dependence upon the total number of spikes, renders comparison of spike-field coherence across experimental context difficult. In this paper, an inferential procedure based upon a generalized linear model is shown to be capable of separating the effects of overall neural activity from spike train-LFP oscillatory coupling. This separation provides a means to compare the strength of oscillatory association between spike train-LFP pairs independent of differences in spike counts.
Following a review of the generalized linear modelling framework of point process neural activity a specific class of generalized linear models are introduced. This model class, using either a piece-wise constant link function, or an exponential function to relate an LFP rhythm to neural response, is used to develop hypothesis tests capable of detecting changes in spike train-LFP oscillatory coupling. The performance of these tests is validated, both in simulation and on real data. The proposed method of inference provides a principled statistical procedure by which across-context change in spike train-LFP rhythmic association can be directly inferred that explicitly handles between-condition differences in total spike count.
Receptive fields (RFs) of cortical sensory neurons increase in size along consecutive processing stages. When multiple stimuli are present in a large visual RF, a neuron typically responds to an attended stimulus as if only that stimulus were present. However, the mechanism by which a neuron selectively responds to a subset of its inputs while discarding all others is unknown. Here, we show that neurons can switch between subsets of their afferent inputs by highly specific modulations of interareal gamma-band phase-coherence (PC). We measured local field potentials, single- and multi-unit activity in two male macaque monkeys (Macaca mulatta) performing an attention task. Two small stimuli were placed on a screen; the stimuli were driving separate local V1 populations, while both were driving the same local V4 population. In each trial, we cued one of the two stimuli to be attended. We found that gamma-band PC of the local V4 population with multiple subpopulations of its V1 input was differentially modulated. It was high with the input subpopulation representing the attended stimulus, while simultaneously it was very low between the same V4 population and the other input-providing subpopulation representing the irrelevant stimulus. These differential modulations, which depend on stimulus relevance, were also found in the locking of spikes from V4 neurons to the gamma-band oscillations of the V1 input subpopulations. This rapid, highly specific interareal locking provides neurons with a powerful dynamic routing mechanism to select and process only the currently relevant signals.
Alpha-band oscillations are the dominant oscillations in the human brain and recent evidence suggests that they have an inhibitory function. Nonetheless, there is little doubt that alpha-band oscillations also play an active role in information processing. In this article, I suggest that alpha-band oscillations have two roles (inhibition and timing) that are closely linked to two fundamental functions of attention (suppression and selection), which enable controlled knowledge access and semantic orientation (the ability to be consciously oriented in time, space, and context). As such, alpha-band oscillations reflect one of the most basic cognitive processes and can also be shown to play a key role in the coalescence of brain activity in different frequencies.
Selective attention mechanisms route behaviorally relevant information through large-scale cortical networks. Although evidence suggests that populations of cortical neurons synchronize their activity to preferentially transmit information about attentional priorities, it is unclear how cortical synchrony across a network is accomplished. Based on its anatomical connectivity with the cortex, we hypothesized that the pulvinar, a thalamic nucleus, regulates cortical synchrony. We mapped pulvino-cortical networks within the visual system, using diffusion tensor imaging, and simultaneously recorded spikes and field potentials from these interconnected network sites in monkeys performing a visuospatial attention task. The pulvinar synchronized activity between interconnected cortical areas according to attentional allocation, suggesting a critical role for the thalamus not only in attentional selection but more generally in regulating information transmission across the visual cortex.
Studying the laminar pattern of neural activity is crucial for understanding the processing of neural signals in the cerebral cortex. We measured neural population activity [multiunit spike activity (MUA) and local field potential, LFP] in Macaque primary visual cortex (V1) in response to drifting grating stimuli. Sustained visually driven MUA was at an approximately constant level across cortical depth in V1. However, sustained, visually driven, local field potential power, which was concentrated in the γ-band (20-60 Hz), was greatest at the cortical depth corresponding to cortico-cortical output layers 2, 3, and 4B. γ-band power also tends to be more sustained in the output layers. Overall, cortico-cortical output layers accounted for 67% of total γ-band activity in V1, whereas 56% of total spikes evoked by drifting gratings were from layers 2, 3, and 4B. The high-resolution layer specificity of γ-band power, the laminar distribution of MUA and γ-band activity, and their dynamics imply that neural activity in V1 is generated by laminar-specific mechanisms. In particular, visual responses of MUA and γ-band activity in cortico-cortical output layers 2, 3, and 4B seem to be strongly influenced by laminar-specific recurrent circuitry and/or feedback.
Slices of sensorimotor and anterior cingulate cortex from guinea pigs were maintained in vitro and bathed in a normal physiological medium. Electrophysiological properties of neurons were assessed with intracellular recording techniques. Some neurons were identified morphologically by intracellular injection of the fluorescent dye Lucifer yellow CH. Three distinct neuronal classes of electrophysiological behavior were observed; these were termed regular spiking, bursting, and fast spiking. The physiological properties of neurons from sensorimotor and anterior cingulate areas did not differ significantly. Regular-spiking cells were characterized by action potentials with a mean duration of 0.80 ms at one-half amplitude, a ratio of maximum rate of spike rise to maximum rate of fall of 4.12, and a prominent afterhyperpolarization following a train of spikes. The primary slope of initial spike frequency versus injected current intensity was 241 Hz/nA. During prolonged suprathreshold current pulses the frequency of firing adapted strongly. When local synaptic pathways were activated, all cells were transiently excited and then strongly inhibited. Bursting cells were distinguished by their ability to generate endogenous, all-or-none bursts of three to five action potentials. Their properties were otherwise very similar to regular-spiking cells. The ability to generate a burst was eliminated when the membrane was depolarized to near the firing threshold with tonic current. By contrast, hyperpolarization of regular-spiking (i.e., nonbursting) cells did not uncover latent bursting tendencies. The action potentials of fast-spiking cells were much briefer (mean of 0.32 ms) than those of the other cell types.(ABSTRACT TRUNCATED AT 250 WORDS)
In recent years, many new cortical areas have been identified in the macaque monkey. The number of identified connections between areas has increased even more dramatically. We report here on (1) a summary of the layout of cortical areas associated with vision and with other modalities, (2) a computerized database for storing and representing large amounts of information on connectivity patterns, and (3) the application of these data to the analysis of hierarchical organization of the cerebral cortex. Our analysis concentrates on the visual system, which includes 25 neocortical areas that are predominantly or exclusively visual in function, plus an additional 7 areas that we regard as visual-association areas on the basis of their extensive visual inputs. A total of 305 connections among these 32 visual and visual-association areas have been reported. This represents 31% of the possible number of pathways it each area were connected with all others. The actual degree of connectivity is likely to be closer to 40%. The great majority of pathways involve reciprocal connections between areas. There are also extensive connections with cortical areas outside the visual system proper, including the somatosensory cortex, as well as neocortical, transitional, and archicortical regions in the temporal and frontal lobes. In the somatosensory/motor system, there are 62 identified pathways linking 13 cortical areas, suggesting an overall connectivity of about 40%. Based on the laminar patterns of connections between areas, we propose a hierarchy of visual areas and of somato sensory/motor areas that is more comprehensive than those suggested in other recent studies. The current version of the visual hierarchy includes 10 levels of cortical processing. Altogether, it contains 14 levels if one includes the retina and lateral geniculate nucleus at the bottom as well as the entorhinal cortex and hippocampus at the top. Within this hierarchy, there are multiple, intertwined processing streams, which, at a low level, are related to the compartmental organization of areas V1 and V2 and, at a high level, are related to the distinction between processing centers in the temporal and parietal lobes. However, there are some pathways and relationships (about 10% of the total) whose descriptions do not fit cleanly into this hierarchical scheme for one reason or another. In most instances, though, it is unclear whether these represent genuine exceptions to a strict hierarchy rather than inaccuracies or uncertainties in the reported assignment.
The biomedical sciences have recently undergone revolutionary change, due to the ability to digitize and store large data sets. In neuroscience, the data sources include measurements of neural activity measured using electrode arrays, EEG and MEG, brain imaging data from PET, fMRI, and optical imaging methods. Analysis, visualization, and management of these time series data sets is a growing field of research that has become increasingly important both for experimentalists and theorists interested in brain function. The first part of the book contains a set of chapters which provide non-technical conceptual background to the subject. Salient features include the adoption of an active perspective of the nervous system, an emphasis on function, and a brief survey of different theoretical accounts in neuroscience. The second part is the longest in the book, and contains a refresher course in mathematics and statistics leading up to time series analysis techniques. The third part contains applications of data analysis techniques to the range of data sources indicated above, and the fourth part contains special topics.
An increasingly large body of data exists which demonstrates that oscillations of frequency 12-80 Hz are a consequence of, or are inextricably linked to, the behaviour of inhibitory interneurons in the central nervous system. This frequency range covers the EEG bands beta 1 (12-20 Hz), beta 2 (20-30 Hz) and gamma (30-80 Hz). The pharmacological profile of both spontaneous and sensory-evoked EEG potentials reveals a very strong influence on these rhythms by drugs which have direct effects on GABA(A) receptor-mediated synaptic transmission (general anaesthetics, sedative/hypnotics) or indirect effects on inhibitory neuronal function (opiates, ketamine). In addition, a number of experimental models of, in particular, gamma-frequency oscillations, have revealed both common denominators for oscillation generation and function, and subtle differences in network dynamics between the different frequency ranges. Powerful computer and mathematical modelling techniques based around both clinical and experimental observations have recently provided invaluable insight into the behaviour of large networks of interconnected neurons. In particular, the mechanistic profile of oscillations generated as an emergent property of such networks, and the mathematical derivation of this complex phenomenon have much to contribute to our understanding of how and why neurons oscillate. This review will provide the reader with a brief outline of the basic properties of inhibition-based oscillations in the CNS by combining research from laboratory models, large-scale neuronal network simulations, and mathematical analysis.
We review evidence for partially segregated networks of brain areas that carry out different attentional functions. One system, which includes parts of the intraparietal cortex and superior frontal cortex, is involved in preparing and applying goal-directed (top-down) selection for stimuli and responses. This system is also modulated by the detection of stimuli. The other system, which includes the temporoparietal cortex and inferior frontal cortex, and is largely lateralized to the right hemisphere, is not involved in top-down selection. Instead, this system is specialized for the detection of behaviourally relevant stimuli, particularly when they are salient or unexpected. This ventral frontoparietal network works as a 'circuit breaker' for the dorsal system, directing attention to salient events. Both attentional systems interact during normal vision, and both are disrupted in unilateral spatial neglect.
Attention can be focused volitionally by “top-down” signals derived from task demands and automatically by “bottom-up” signals from salient stimuli. The frontal and parietal cortices are involved, but their neural activity has not been directly compared. Therefore, we recorded from them simultaneously in monkeys. Prefrontal neurons reflected the target location first during top-down attention, whereas parietal neurons signaled it earlier during bottom-up attention. Synchrony between frontal and parietal areas was stronger in lower frequencies during top-down attention and in higher frequencies during bottom-up attention. This result indicates that top-down and bottom-up signals arise from the frontal and sensory cortex, respectively, and different modes of attention may emphasize synchrony at different frequencies.
In crowded visual scenes, attention is needed to select relevant stimuli. To study the underlying mechanisms, we recorded
neurons in cortical area V4 while macaque monkeys attended to behaviorally relevant stimuli and ignored distracters. Neurons
activated by the attended stimulus showed increased gamma-frequency (35 to 90 hertz) synchronization but reduced low-frequency
(<17 hertz) synchronization compared with neurons at nearby V4 sites activated by distracters. Because postsynaptic integration
times are short, these localized changes in synchronization may serve to amplify behaviorally relevant signals in the cortex.
Visual cortical areas subserve cognitive functions by interacting in both feedforward and feedback directions. While feedforward influences convey sensory signals, feedback influences modulate feedforward signaling according to the current behavioral context. We investigated whether these interareal influences are subserved differentially by rhythmic synchronization. We correlated frequency-specific directed influences among 28 pairs of visual areas with anatomical metrics of the feedforward or feedback character of the respective interareal projections. This revealed that in the primate visual system, feedforward influences are carried by theta-band
(4 Hz) and gamma-band (60–80 Hz) synchronization, and feedback influences by beta-band (14–18 Hz) synchronization. The functional directed influences constrain a functional hierarchy similar tothe anatomical hierarchy, but exhibiting task-dependent dynamic changes in particular with regard to the hierarchical positions of frontal areas. Our results demonstrate that feedforward and feedback signaling use distinct frequency channels, suggesting that they subserve differential communication requirements.
Selective visual attention is subserved by selective neuronal synchronization, entailing precise orchestration among excitatory and inhibitory cells. We tentatively identified these as broad (BS) and narrow spiking (NS) cells and analyzed their synchronization to the local field potential in two macaque monkeys performing a selective visual attention task. Across cells, gamma phases scattered widely but were unaffected by stimulation or attention. During stimulation, NS cells lagged BS cells on average by ∼60° and gamma synchronized twice as strongly. Attention enhanced and reduced the gamma locking of strongly and weakly activated cells, respectively. During a prestimulus attentional cue period, BS cells showed weak gamma synchronization, while NS cells gamma-synchronized as strongly as with visual stimulation. These analyses reveal the cell-type-specific dynamics of the gamma cycle in macaque visual cortex and suggest that attention affects neurons differentially depending on cell type and activation level.
Wiener-Granger causality ("G-causality") is a statistical notion of causality applicable to time series data, whereby cause precedes, and helps predict, effect. It is defined in both time and frequency domains, and allows for the conditioning out of common causal influences. Originally developed in the context of econometric theory, it has since achieved broad application in the neurosciences and beyond. Prediction in the G-causality formalism is based on VAR (Vector AutoRegressive) modelling. New Method: The MVGC Matlab Toolbox approach to G-causal inference is based on multiple equivalent representations of a VAR model by (i) regression parameters, (ii) the autocovariance sequence and (iii) the cross-power spectral density of the underlying process. It features a variety of algorithms for moving between these representations, enabling selection of the most suitable algorithms with regard to computational efficiency and numerical accuracy.
In this paper we explain the theoretical basis, computational strategy and application to empirical G-causal inference of the MVGC Toolbox. We also show via numerical simulations the advantages of our Toolbox over previous methods in terms of computational accuracy and statistical inference. Comparison with Existing Method(s): The standard method of computing G-causality involves estimation of parameters for both a full and a nested (reduced) VAR model. The MVGC approach, by contrast, avoids explicit estimation of the reduced model, thus eliminating a source of estimation error and improving statistical power, and in addition facilitates fast and accurate estimation of the computationally awkward case of conditional G-causality in the frequency domain.
The MVGC Toolbox implements a flexible, powerful and efficient approach to G-causal inference.
Muscarinic signaling affects attention, action selection, learning, and memory through multiple signaling cascades, which act at different timescales and which alter ion channels in cell type-specific manners. The effects of muscarinic signaling differ between cortical layers and between brain areas. Muscarinic signaling adds flexibility to the processing mode of neuronal networks, thereby supporting processing according to task demands. This review outlines possible scenarios to describe how it contributes to cellular mechanisms of attention and how it affects channeling of information in different neuronal circuits.
Recent studies have shown that neurons in area 17 of cat visual cortex display oscillatory responses which can synchronize across spatially separate orientation columns. Here, we demonstrate that unit responses recorded from the posteromedial lateral suprasylvian area, a visual association area specialized for the analysis of motion, also exhibit an oscillatory temporal structure. Cross-correlation analysis of unit responses reveals that cells in area 17 and the posteromedial lateral suprasylvian area can oscillate synchronously. Moreover, we find that the interareal synchronization is sensitive to features of the visual stimuli, such as spatial continuity and coherence of motion. These results support the hypothesis that synchronous neuronal oscillations may serve to establish relationships between features processed in different areas of visual cortex.
Current theories propose that coherence of oscilla-tory brain activity in the gamma band (30–80 Hz) constitutes an avenue for communication among remote neural populations. However, reports documenting stimulus dependency and time variability of gamma frequency suggest that distant neuronal populations may, at any one time, operate at different frequencies precluding synchronization. To test this idea, we recorded from macaque V1 and V2 simultaneously while presenting gratings of varying contrast. Although gamma frequency increased with stimulus contrast in V1 and V2 (by $25 Hz), V1-V2 gamma coherence was maintained for all contrasts. Moreover , while gamma frequency fluctuated by $15 Hz during constant contrast stimulation, this fluctuation was highly correlated between V1 and V2. The strongest coherence connections showed a layer-specific pattern, matching feedforward anatomical connec-tivity. Hence, gamma coherence among remote populations can occur despite large stimulus-induced and time-dependent changes in gamma frequency, allowing communication through coherence to operate without a stimulus independent, fixed-frequency gamma channel.
Gamma components of the local field potential (LFP) are elevated during cognitive and perceptual processes. It has been suggested that gamma power indicates the strength of neuronal population synchrony, which influences the relaying of signals between cortical areas. However, the relationship between coordinated spiking activity and gamma remains unclear, and the influence on corticocortical signaling largely untested. We investigated these issues by recording from neuronal populations in areas V1 and V2 of anesthetized macaque monkeys. We found that visual stimuli that induce a strong, coherent gamma rhythm result in enhanced pairwise and higher-order V1 synchrony. This is associated with stronger coupling of V1-V2 spiking activity, in a retinotopically specific manner. Coupling is more strongly related to the gamma modulation of V1 firing than to the downstream V2 rhythm. Our results thus show that elevated gamma power is associated with stronger coordination of spiking activity both within and between cortical areas.
A central motif in neuronal networks is convergence, linking several input neurons to one target neuron. In visual cortex, convergence renders target neurons responsive to complex stimuli. Yet, convergence typically sends multiple stimuli to a target, and the behaviorally relevant stimulus must be selected. We used two stimuli, activating separate electrocorticographic V1 sites, and both activating an electrocorticographic V4 site equally strongly. When one of those stimuli activated one V1 site, it gamma synchronized (60-80 Hz) to V4. When the two stimuli activated two V1 sites, primarily the relevant one gamma synchronized to V4. Frequency bands of gamma activities showed substantial overlap containing the band of interareal coherence. The relevant V1 site had its gamma peak frequency 2-3 Hz higher than the irrelevant V1 site and 4-6 Hz higher than V4. Gamma-mediated interareal influences were predominantly directed from V1 to V4. We propose that selective synchronization renders relevant input effective, thereby modulating effective connectivity.