Cortical and Sensory Systems
Daniel Ts'o, PhD,
Associate Professor
Neuronal Mechanisms of Visual Perception
Structure and function of primate visual cortex
The long-term goal of our work is to arrive at a deeper understanding of the neural mechanisms underlying visual perception. Although we have chosen to focus on the processing in the visual system, the mechanisms of neuronal organization, interaction and connectivity that we are studying hold broad implications for our understanding of brain in both normal and diseased states. One important theme concerns the classes of neuronal interactions between different cortical areas, the study of which should lead to an understanding of why and how the brain is divided up into so many areas, many of which seem to have functions that to some degree overlap with those of other areas. We are studying how the various visual areas interact, what kinds of information are passed between these areas, why multiple cortical areas instead of one are necessary, and how in general do multiple cortical areas cooperate with each other. A second theme in our research addresses the types of functional organization in the neocortex, just how segregated each functional domain is, what the different patterns of organization are, and how functional domains interact within a given cortical region. These studies have important implications for our understanding of how the cortex represents multiple processing dimensions in the same cortical area.
Our research should not only lead to a better understanding of the nature of brain function and architecture, but will provide insights into disease states that involve neuronal connectivity, such as Alzheimer's and epilepsy, as well as central visual disorders.
Our studies in non-human primates, using anatomical, physiological and functional imaging techniques, have revealed separate pathways for distinct aspects of visual processing. Optical imaging results show a patchwork of cortical modules or cortical maps dedicated to visual features, such as form, color and depth. Multi-electrode single-cell electrophysiology has shown both the properties of individual neurons, and how ensembles of neurons cooperate to ultimately yield visual perception, object recognition and visually-guided behavior.
Noninvasive retinal imaging. We have adapted the technique of intrinsic signal optical imaging of neural activity to the noninvasive functional imaging of retina, and demonstrated the feasibility and potential of this new method for the functional assessment of the retina. Like its counterpart for studies of neocortex, this retinal functional imaging technique measures functionally correlated intrinsic optical signals in the retina such as total hemoglobin concentration and deoxy/oxy-hemoglobin exchange. Via a modified fundus camera, this technique enables us to visualize the patterns of activity in the intact retina while presenting visual stimuli. The most anticipated applications of this technology are those in ophthalmology, in the study, diagnosis and treatment of retinal diseases, as well as in basic research of retinal function.
Functional mapping of the human visual system. Recent fMRI studies of retinotopic maps of the early visual areas (e.g. V1, V2) have shown a high degree of correspondence with those of non-human primates. This allows us the opportunity to study the human visual system in a way that is complementary to the anatomical and physiological studies that have been done with non-human primates. We are specifically interested in the mechanisms underlying color and form perception. In a recently published study, we examined the possibility of a common pathway and cortical locus for perceptual decision making, regardless of the modality of the input stimulus. In human subjects performing visual and auditory discriminations, we discovered such a common site in the posterior bank of the intraparietal sulcus (PIPS). Future studies will examine interactions between the color and form pathways in the human visual system.
—Daniel Ts'o, Sean Huckins, Nikolaus Szeverenyi
