Transient Cortical Excitation at the Onset of Visual Fixation

Cognitive Neuroscience and Schizophrenia Program, Nathan S. Kline Institute for Psychiatric Research, Orangeburg, NY 10962, USA.
Cerebral Cortex (Impact Factor: 8.67). 02/2008; 18(1):200-9. DOI: 10.1093/cercor/bhm046
Source: PubMed


Primates actively examine the visual world by rapidly shifting gaze (fixation) over the elements in a scene. Despite this fact, we typically study vision by presenting stimuli with gaze held constant. To better understand the dynamics of natural vision, we examined how the onset of visual fixation affects ongoing neuronal activity in the absence of visual stimulation. We used multiunit activity and current source density measurements to index neuronal firing patterns and underlying synaptic processes in macaque V1. Initial averaging of neural activity synchronized to the onset of fixation suggested that a brief period of cortical excitation follows each fixation. Subsequent single-trial analyses revealed that 1) neuronal oscillation phase transits from random to a highly organized state just after the fixation onset, 2) this phase concentration is accompanied by increased spectral power in several frequency bands, and 3) visual response amplitude is enhanced at the specific oscillatory phase associated with fixation. We hypothesize that nonvisual inputs are used by the brain to increase cortical excitability at fixation onset, thus "priming" the system for new visual inputs generated at fixation. Despite remaining mechanistic questions, it appears that analysis of fixation-related responses may be useful in studying natural vision.

Download full-text


Available from: Peter Lakatos, May 23, 2014
  • Source
    • "retinal image during saccades could activate visual gain control mechanisms that transiently enhance visual sensitivity . Previous experiments have demonstrated that post - saccadic enhancement of spontaneous neural activity occurs even in complete darkness ( cat : Lee and Malpeli , 1998 ; monkey : Reppas et al . , 2002 ; Ibbotson et al . , 2008 ; Rajkai et al . , 2008 ) . While this is good evidence for an internal mechanism , modulation of spontaneous rate may not be linked directly to changes in sensitivity to visual stimulation . Therefore , before a mechanism can be identified a major question remains : does visual input during saccades have any influence on post - saccadic enhancement or does th"
    [Show abstract] [Hide abstract]
    ABSTRACT: Primates use saccadic eye movements to make gaze changes. In many visual areas, including the dorsal medial superior temporal area (MSTd) of macaques, neural responses to visual stimuli are reduced during saccades but enhanced afterwards. How does this enhancement arise-from an internal mechanism associated with saccade generation or through visual mechanisms activated by the saccade sweeping the image of the visual scene across the retina? Spontaneous activity in MSTd is elevated even after saccades made in darkness, suggesting a central mechanism for post-saccadic enhancement. However, based on the timing of this effect, it may arise from a different mechanism than occurs in normal vision. Like neural responses in MSTd, initial ocular following eye speed is enhanced after saccades, with evidence suggesting both internal and visually mediated mechanisms. Here we recorded from visual neurons in MSTd and measured responses to motion stimuli presented soon after saccades and soon after simulated saccades-saccade-like displacements of the background image during fixation. We found that neural responses in MSTd were enhanced when preceded by real saccades but not when preceded by simulated saccades. Furthermore, we also observed enhancement following real saccades made across a blank screen that generated no motion signal within the recorded neurons' receptive fields. We conclude that in MSTd the mechanism leading to post-saccadic enhancement has internal origins.
    Frontiers in Systems Neuroscience 09/2015; 9:122. DOI:10.3389/fnsys.2015.00122
  • Source
    • "Additionally, because our measure of synchrony was based on spontaneous activity, it cannot be attributed to co-fluctuations in visually evoked responses . The link also cannot be due to eye movements (Ito et al. 2011; Rajkai et al. 2008 "
    [Show abstract] [Hide abstract]
    ABSTRACT: Investigating the relationship between tuning and spike timing is necessary to understand how neuronal populations in anterior visual cortex process complex stimuli. Are tuning and spontaneous spike time synchrony linked by a common spatial structure (do some cells co- vary more strongly, even in the absence of visual stimulation?), and what is the object coding capability of this structure? Here, we recorded from spiking populations in macaque inferior temporal (IT) cortex under neurolept anesthesia. We report that although most nearby IT neurons are weakly correlated, neurons with more similar tuning are also more synchronized during spontaneous activity. This link between tuning and synchrony was not simply due to cell separation distance. Instead, it expands on previous reports that neurons along an IT penetration are tuned to similar but slightly different features. This constraint on possible population firing rate patterns was consistent across stimulus sets, including animate versus inanimate object categories. A classifier trained on this structure was able to generalize category 'read-out' to untrained objects using only a few dimensions (a few patterns of site weightings per electrode array). We suggest that tuning and spike synchrony are linked by a common spatial structure that is highly efficient for object representation.
    Journal of Neurophysiology 05/2014; 112(4). DOI:10.1152/jn.00485.2013 · 2.89 Impact Factor
  • Source
    • "The anatomical origins of the motor-related phase-resetting cues are uncertain, but plausible candidates are efference copies from the oculomotor system (pontine reticular formation and/or extraocular muscles, see Ito et al., 2011) or a corollary discharge route through the superior colliculus (SC), thalamus, and frontal eye fields (FEFs) (see Melloni et al., 2009). It is also possible that saccades and the corollary activity are both generated in parallel by attention (Melloni et al., 2009; Rajkai et al., 2008). (B) Selective attention orchestrates phase resetting of oscillations in auditory and visual cortices (e.g., Lakatos et al., 2008). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Research into the anatomical substrates and "principles" for integrating inputs from separate sensory surfaces has yielded divergent findings. This suggests that multisensory integration is flexible and context dependent and underlines the need for dynamically adaptive neuronal integration mechanisms. We propose that flexible multisensory integration can be explained by a combination of canonical, population-level integrative operations, such as oscillatory phase resetting and divisive normalization. These canonical operations subsume multisensory integration into a fundamental set of principles as to how the brain integrates all sorts of information, and they are being used proactively and adaptively. We illustrate this proposition by unifying recent findings from different research themes such as timing, behavioral goal, and experience-related differences in integration.
    Neuron 03/2014; 81(6):1240-1253. DOI:10.1016/j.neuron.2014.02.044 · 15.05 Impact Factor
Show more