Sergio Neuenschwander

Sergio Neuenschwander
Universidade Federal do Rio Grande do Norte | IIP · Brain Institute

PhD

About

66
Publications
7,507
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3,698
Citations
Additional affiliations
October 1994 - January 1995
Federal University of Minas Gerais
February 1992 - December 2010
April 1989 - January 1991
Sorbonne Université
Position
  • Institut des Neurosciences

Publications

Publications (66)
Preprint
Full-text available
Fast gamma oscillations, generated within the retina, and transmitted to the cortex via the lateral geniculate nucleus (LGN), are thought to carry information about stimulus size and continuity. This hypothesis relies mainly on studies carried out under anesthesia and the extent to which it holds under more naturalistic conditions remains unclear....
Article
Full-text available
Circuits of excitatory and inhibitory neurons generate gamma-rhythmic activity (30–80 Hz). Gamma-cycles show spontaneous variability in amplitude and duration. To investigate the mechanisms underlying this variability, we recorded local-field-potentials (LFPs) and spikes from awake macaque V1. We developed a noise-robust method to detect gamma-cycl...
Article
We propose in this work a new method for estimating the main mode of multivariate distributions, with application to eye-tracking calibration. When performing eye-tracking experiments with poorly cooperative subjects, such as infants or monkeys, the calibration data generally suffer from high contamination. Outliers are typically organized in clust...
Preprint
Full-text available
We propose in this work a new method for estimating the main mode of multivariate distributions, with application to eye-tracking calibrations. When performing eye-tracking experiments with poorly cooperative subjects, such as infants or monkeys, the calibration data generally suffer from high contamination. Outliers are typically organized in clus...
Article
Full-text available
Cortical computation depends on interactions between excitatory and inhibitory neurons. The contributions of distinct neuron types to sensory processing and network synchronization in primate visual cortex remain largely undetermined. We show that in awake monkey V1, there exists a distinct cell type (››30% of neurons) that has narrow-waveform (NW)...
Preprint
Full-text available
Communication among visual cortical areas depends on gamma oscillations. Respective gamma cycles vary substantially in amplitude and duration, yet it is unclear how those fundamental parameters relate to each other and to spiking activity. We recorded local-field-potentials (LFPs) and spiking activity from awake macaque area V1 and detected amplitu...
Article
Full-text available
One leading hypothesis on the nature of visual callosal connections (CC) is that they replicate features of intrahemispheric lateral connections. However, CC act also in the central part of the binocular visual field. In agreement, early experiments in cats indicated that they provide the ipsilateral eye part of binocular receptive fields (RFs) at...
Conference Paper
Full-text available
Contour elements of static and dynamic visual stimuli are more accurately detected and discriminated when aligned with the horizontal and vertical axes than when obliquely oriented. This phenomenon, known as the "oblique effect", has been observed in a great variety of visual tasks and for animal species as diverse as goldfishes, octopuses, pigeons...
Conference Paper
Full-text available
Gamma oscillations in the retina are transmitted to the lateral geniculate nucleus (LGN) and to the cortex, and are thought to encode stimulus size and continuity. Support for these conjectures were obtained mostly in the anesthetized cat, and visual stimuli were often limited to whole-field flashes. Here, we aim filling this gap by characterizing...
Conference Paper
Full-text available
Cortical gamma oscillations have been implicated in perceptual binding and visual attention. So far, most evidence in support of this hypothesis are based on studies that used artificial, simplified stimuli, such as moving gratings and bars. Recently, a more naturalistic approach led to diverging conclusions. In human subjects required to hold fixa...
Preprint
Full-text available
Sensory cortices represent the world through the activity of diversely tuned cells. How the activity of single cells is coordinated within populations and across sensory hierarchies is largely unknown. Cortical oscillations may coordinate local and distributed neuronal groups. Using datasets from intracortical multi-electrode recordings and from la...
Article
Full-text available
Even in V1, where neurons have well characterized classical receptive fields (CRFs), it has been difficult to deduce which features of natural scenes stimuli they actually respond to. Forward models based upon CRF stimuli have had limited success in predicting the response of V1 neurons to natural scenes. As natural scenes exhibit complex spatial a...
Data
Varying aperture mask size. The percentage of the PSTH that was statistically different (at 95% confidence levels) between FF and AM movies (upper panel) and the normalized difference in time varying firing rates (lower panel) for different sized apertures. There are (38, 13 38, 38, 38, 19) neurons for the (30, 50, 70, 100, 150, 200 pixel) diameter...
Data
Comparing differences between the PSTHs as a function of eccentricity (2-5 degrees versus 10-14 degrees). A) Percentage of PSTH statistically different, B) normalized difference between PSTHs, C) normalized mean firing rate difference between PSTHs. Distributions are all identical (via KS test) between 2-5 and 10-14 degrees except for the normalize...
Data
Three examples (columns) of aperture mask placement. Top row: movie frame. Second row: CRFs of multiunit activity of recording electrodes. (Example in left column records from both 2-5 degrees eccentricity and 10-14 degrees, i.e. two different electrodes). Third row: aperture masks generated on-line. Bottom row: aperture masks overlaid on CRFs. Not...
Data
Spike waveforms isolated from multiunit activity. Waveforms of the three neurons whose PSTHs are presented in the paper (Figure 1 & Figure S4) are shown in red. Grey shows non-isolated background spikes (MUA). (TIF)
Data
Quantifying spike leakage into the LFP. A) Spike triggered averages from 9 representative neurons. Dark blue: STA of original LFP, Light blue: STA of compound LFP generated using original spike times, Red: STA of compound LFP generated using altered spike times. STAs of the original and first compound LFPs are highly similar indicating that our pro...
Data
Grating stimuli drive strong oscillations that are not observed during natural scenes. A) Z-scored power spectra for LFP and B) MUA during 1.875 Hz grating stimulus (speed 1.5 degree/s and spatial frequency 1.25 cycles per degree) (green) and natural scenes movies (black). C) Frequency dependent coherence between LFP and MUA. Z-scored power spectra...
Data
“Sharp” LFP oscillations cause crosstalk between frequencies. A) sMRA of a 70 Hz sawtooth (black) involves high frequency harmonics (colored curves) to capture its “sharpness”. B) “Preferred” LFP scale phases (at which the GLM predicts the highest probability of spiking) of the 44, 89 and 178 Hz scales compared across all neurons. C) Scatterplot of...
Data
Percentages of neurons for which different nested models passed statistical validation tests. LL: The log likelihood of the test data was greater for the more complicated model than for the next simplest model. AIC: The Akaike Information Criterion of the more complex model was smaller than that of the simpler model. BIC test: Same but using the Ba...
Data
Details on spike sorting, control of LFP “leakage” into spikes, calculation of confidence bounds on GLM fits, goodness of fit of GLM to trial averaged PSTHs and the effect of eccentricity on results. (DOC)
Data
PSTHs of two additional V1 neurons. These exhibit significantly different stimulus locked firing responses to natural scenes stimuli when the surround is changed but the CRF stimulus is not. As in the main text, upper panels show GLM fitted “PSTHs” (blue = FF, green = AM, red = TR) and lower panels show differences (in yellow) between PSTHs. Lighte...
Data
Spline based GLM models accurately fit trial averaged firing rate (PSTH). A) PSTHs (20 ms histogram) and spline fits (red) for two example neurons under natural scenes stimulation. B) Distribution of explained variance of training data (left), test data (middle) and test data corrected for finite number of test data trials (right). C) Splines used...
Article
Full-text available
The moving bar experiment is a classic paradigm for characterizing the receptive field (RF) properties of neurons in primary visual cortex (V1). Current approaches for analyzing neural spiking activity recorded from these experiments do not take into account the point-process nature of these data and the circular geometry of the stimulus presentati...
Article
Full-text available
Gamma-band synchronization adjusts the timing of excitatory and inhibitory inputs to a neuron. Neurons in the visual cortex are selective for stimulus orientation because of dynamic interactions between excitatory and inhibitory inputs. We hypothesized that these interactions and hence also orientation selectivity vary during the gamma cycle. We de...
Article
Full-text available
Gamma oscillations have been linked to selective attention. Here, we investigate the effects of expecting a behaviorally relevant event (a change in the fixation point) on the oscillatory patterning of the local field potential and spiking responses in V1. Three protocols were used. In the first protocol, fixation point change occurred at a fixed t...
Article
Full-text available
The simultaneous recording of the activity of many neurons poses challenges for multivariate data analysis. Here, we propose a general scheme of reconstruction of the functional network from spike train recordings. Effective, causal interactions are estimated by fitting generalized linear models on the neural responses, incorporating effects of the...
Article
γ-band oscillations are thought to play a crucial role in information processing in cortical networks. In addition to oscillatory activity between 30 and 60 Hz, current evidence from electro- and magnetoencephalography (EEG/MEG) and local-field potentials (LFPs) has consistently shown oscillations >60 Hz (high γ-band) whose function and generating...
Article
Full-text available
Gamma-band synchronization is abundant in nervous systems. Typically, the strength or precision of gamma-band synchronization is studied. However, the precise phase with which individual neurons are synchronized to the gamma-band rhythm might have interesting consequences for their impact on further processing and for spike timing-dependent plastic...
Article
Full-text available
Gamma synchronization has generally been associated with grouping processes in the visual system. Here, we examine in monkey V1 whether gamma oscillations play a functional role in segmenting surfaces of plaid stimuli. Local field potentials (LFPs) and spiking activity were recorded simultaneously from multiple sites in the opercular and calcarine...
Article
Full-text available
Following the discovery of context-dependent synchronization of oscillatory neuronal responses in the visual system, the role of neural synchrony in cortical networks has been expanded to provide a general mechanism for the coordination of distributed neural activity patterns. In the current paper, we present an update of the status of this hypothe...
Article
The avian retinothalamofugal pathway reaches the telencephalon in an area known as visual wulst. A close functional analogy between this area and the early visual cortex of mammals has been established in owls. The goal of the present study was to assess quantitatively the directional selectivity and motion integration capability of visual wulst ne...
Article
In cat visual cortex, we investigated with parallel recordings from multiple units the neuronal correlates of perceived brightness. The perceived brightness of a center grating was changed by varying the orientation or the relative spatial phase of a surrounding grating. Brightness enhancement by orientation contrast is associated with an increase...
Article
Full-text available
We show that coherent oscillations among neighboring ganglion cells in a retinal model encode global topological properties, such as size, that cannot be deduced unambiguously from their local, time-averaged firing rates. Whereas ganglion cells may fire similar numbers of spikes in response to both small and large spots, only large spots evoke cohe...
Article
Full-text available
Visual responses in the cortex and lateral geniculate nucleus (LGN) are often associated with synchronous oscillatory patterning. In this short review, we examine the possible relationships between subcortical and cortical synchronization mechanisms. Our results obtained from simultaneous multi-unit recordings show strong synchronization of oscilla...
Article
Full-text available
Numerous imaging studies have contributed to the localization of motion-sensitive areas in the human brain. It is, however, still unclear how these areas contribute to global motion perception. Here, we investigate with functional MRI whether the motion-sensitive area hMT+/V5 is involved in perceptual segmentation and integration of motion signals....
Article
Full-text available
Spontaneous brain activity could affect processing if it were structured. We show that neuron pairs in cat primary visual cortex exhibited correlated fluctuations in response latency, particularly when they had overlapping receptive fields or similar orientation preferences. Correlations occurred within and across hemispheres, but only when local f...
Article
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Article
Oscillatory firing of neurons in response to visual stimuli has been observed to occur with different frequencies at multiple levels of the visual system. In the cat retina, oscillatory firing patterns occur with frequencies in the range of 60 to 120 Hz (omega-oscillations). These millisecond-precise temporal patterns are transmitted reliably to th...
Article
Full-text available
To analyse an image, the visual system must decompose the scene into its relevant parts. Identifying distinct surfaces is a basic operation in such analysis, and is believed to precede object recognition. Two superimposed gratings moving in different directions (plaid stimuli) may be perceived either as two surfaces, one being transparent and slidi...
Article
Retinal ganglion cells exhibit oscillatory responses which are precisely synchronized over large distances. Here we examined, with multi-electrode recordings, the time course of synchronization during spontaneous and stimulus-driven oscillatory activity. Spontaneous discharges showed synchronized oscillations at approximately 30 Hz, which were occa...
Article
Full-text available
Neuronal response synchronization with millisecond precision has been proposed to serve feature binding in vision and should therefore, like visual experience, depend on central states. Here we test this hypothesis by examining the occurrence and strength of response synchronization in areas 17 and 18 of anesthetized cats as a function of central s...
Article
Full-text available
Synchronization of spatially distributed responses in the cortex is often associated with periodic activity. Recently, synchronous oscillatory patterning was described for visual responses in retinal ganglion cells that is reliably transmitted by the lateral geniculate nucleus (LGN), raising the question of whether oscillatory inputs contribute to...
Article
The ease with which highly developed brains can generate representations of a virtually unlimited diversity of perceptual objects indicates that they have developed very efficient mechanisms to analyse and represent relations among incoming signals. Here, we propose that two complementary strategies are applied to cope with these combinatorial prob...
Conference Paper
Synchronous oscillations within a broad range of frequencies have been described for visual responses in retinal ganglion cells which are transmitted by the lateral geniculate nucleus (LGN), raising the question of how oscillatory inputs contribute to synchronous oscillatory responses in the cortex. We have made simultaneous recordings from visual...
Article
The question of the presence and detection of non-linear dynamics and possibly low-dimensional chaos in the brain is still an open question, with recent results indicating that initial claims for low dimensionality were faulted by incomplete statistical testing. To make some progress on this question, our approach was to use stringent data analysis...
Article
Full-text available
Multiunit activity was recorded in the optic tectum of awake pigeons with two electrodes at sites varying in depth and separated by 0.3 to 3.0 mm. Autocorrelation and cross-correlation functions were computed from the recorded spike trains to determine temporal relationships in the neuronal firing patterns. Cross-correlation analysis revealed that...
Article
Full-text available
Visual responses in the retina and the lateral geniculate nucleus (LGN) exhibit oscillatory patterning within a broad range of frequencies. Oscillatory activity is often associated with the synchronization of spatially distributed responses. Here we demonstrate, with simultaneous multi-electrode recordings from the retina and the LGN, that stationa...
Article
Two visual areas of the anterior bank of the parietooccipital sulcus, areas PO and POd, were identified and their visual field representations were studied in six anesthetized and paralyzed Cebus monkeys. The definition of these areas was based on electrophysiological mapping and myeloarchitecture. PO is located in the ventral aspect of the anterio...
Article
Multi-unit recordings from the optic tectum of an awake pigeon displaying oscillatory behavior evoked by visual stimulus are highly non-stationary and contain a broad band of frequencies under a time-window analysis. Here we extend these observations by a non-linear dynamical analysis of these oscillatory signals (local fields potentials) in succes...
Article
In this study we describe visually triggered gamma oscillations in the optic tectum of awake pigeons. This study was motivated by the potential relevance of synchronous oscillatory responses in perceptual binding in a laminated structure other than the mammalian neocortex. Tectal responses were recorded as local field potential and multiunit activi...
Article
Full-text available
In this study we describe visually triggered gamma oscillations in the optic tectum of awake pigeons. This study was motivated by the potential relevance of synchronous oscillatory responses in perceptual binding in a laminated structure other than the mammalian neocortex. Tectal responses were recorded as local field potential and multiunit activi...
Article
Full-text available
1. The topographic organization of the cortical visual areas in the Cebus monkey and their anatomical connections support the subdivision of the visual pathways into ventral and dorsal streams of visual information processing. 2. We propose that the dorsal stream, as defined by Ungerleider and Mishkin (In: Ingle DJ, Goodale MA and Mansfield RJW (Ed...
Article
Abstract We present an anatomopathologic study of a case of partial fusion of the mamillary bodies in a 57-year-old man with no neurologic or neuropsychiatric change. Medial nuclei were fused. Remaining nuclei and afferent and efferent connections were preserved. The comparison of this case with other similar malformations suggests the possibility...
Article
São apresentados 30 pacientes portadores de carcinoma avançado do antro gástrico, nos quais se colheram biópsias cranialmente na pequena curvatura, entre 2 e 4 cm da borda macroscópica do tumor. Em quatro casos (13,2%) ncontrou-se tecido neoplásico na mucosa, na submucosa ou na muscular. Como esses tumores ocupam macroscopicamente o terço distal da...

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