Neurophysiology of Visual Perception and Cognition
In my laboratory, we study the neural processes that underlie visual perception and cognition. We use electrophysiological methods to measure neuronal activity in the cerebral cortex and study the relationships between that activity and visually guided behavior. We are currently involved in four areas of research.
The Binding Problem
The visual cortex is organized into a parallel hierarchy of up to 30 separate areas, each of which makes a contribution to the perceptual analysis of visual scenes. How the analysis performed by each visual area comes together to enable a unified perception is one of the great mysteries of the brain and is often referred to as the 'binding problem'.
In my lab, we study the binding problem within a specific theoretical framework referred to as the 'temporal correlation hypothesis'. This set of ideas postulates that visual features in an image are perceptually grouped when populations of neurons in separate parts of the cortex synchronize their activities on a time scale lasting tens to hundreds of milliseconds.
Neuronal Processing of Natural Scenes
The experimental analysis of visual cortex has traditionally used highly artificial stimuli, such as bars or spots of light, or drifting sinusoidal gratings, to determine what properties of visual images excite cortical neurons. While we have learned a great from this approach, many questions remain regarding how the visual system analyzes the complex images that appear in the natural environment. We use electrophysiological techniques to study the relationship between neural activity patterns in the visual cortex and the statistical properties of natural visual images.
Visual Working Memory
Working memory, or what is commonly referred to as 'short term memory', is essential to our cognitive abilities. Without it we would be helpless. We would lack the ability to remember events that we had recently seen or heard. We are investigating the neural processes underlying visual working memory. Our aim is to measure and characterize the patterns of neural activity that occur in the cerebral cortex when a visual object must be held in memory in order to solve a subsequent task.
In order to study perceptual and cognitive processes in the brain, it is necessary to monitor the activities of multiple neurons simultaneously. This is challenging experimental work that requires new forms of instrumentation. We are currently developing a number of new instruments to improve the ease, and increase the yield and reliability, by which such measurements can be made.
Friedman-Hill,S.R., Maldonado,P.E. and Gray,C.M. (2000) Dynamics of Striate Cortical Activity in the Alert Macaque: I. Incidence and Stimulus-Dependence of Gamma-Band Neuronal Oscillations. Cerebral Cortex, 10:1105-1116.
Maldonado,P.E., Friedman-Hill,S.R. and Gray,C.M. (2000) Dynamics of Striate Cortical Activity in the Alert Macaque: II. Fast Time Scale Synchronization. Cerebral Cortex, 10:1117-1131.
Azouz, R. and Gray, C.M. (2003) Adaptive Coincidence Detection and Dynamic Gain Control in Visual Cortical Neurons In Vivo. Neuron, 37:513-523.
Nowak, L.G., Azouz, R.A., Sanchez-Vives, M.V., Gray, C.M. and McCormick, D.A. (2003) Electrophysiological Classes of Cat Primary Visual Cortical Neurons In Vivo as Revealed by Quantitative Analyses. J. Neurophysiol., 89:1541-1566.
Yen, SC, Baker, J, and C.M. Gray (2007) Heterogeneity in the Responses of Adjacent Neurons to Natural Stimuli in Cat Striate Cortex. J. Neurophysiol., 97:1326-1341.
Azouz, R. and Gray, C.M. (2008) Stimulus Selective Spiking is Driven by the Relative Timing of Synchronous Excitation and Disinhibition in Cat Striate Neurons in vivo. Eur. J. Neurosci., 28:1286-1300.
Ito H, Maldonado PE, Gray CM. (2010) Dynamics of stimulus-evoked spike timing correlations in the cat lateral geniculate nucleus. J Neurophysiol., 104:3276-92.