Dr. Gilbert studies the mechanisms underlying visual perception, including the specific role of the brain’s primary visual cortex in analyzing visual images and in visual memory. To this end, his laboratory investigates the circuitry of the brain and how the interactions between groups of neurons contribute to perception, learning and memory.
Dr. Gilbert studies the primary visual cortex, a credit card-sized region of cells at the back of the brain. The primary visual cortex is the initial stage of cortical processing of information from the eye: as light enters the eyes, information is transmitted to the primary visual cortex in millions of pieces that must be assembled and interpreted to create a picture. Dr. Gilbert’s lab discovered a plexus of long-range horizontal connections in the primary visual cortex that mediates this assembly and the parsing of visual scenes into objects and background. The cortex changes the way in which it analyzes sensory information based on past experiences, and there is a close correspondence between the functional properties of neurons in the visual cortex and the perception of visual stimuli: Both neuronal responses and perception depend on the context within which visual features are presented, and both involve integrating information over large parts of visual space. Dr. Gilbert’s lab studies how neurons act as an interactive ensemble through computer models based on these findings.
Using a combination of single-cell electrophysiological recordings, optical imaging of cortical functional architecture and imaging of labeled cortical connections, Dr. Gilbert has also investigated the relationship between connectivity and the functional architecture of visual cortical areas. In a series of experiments, Dr. Gilbert’s lab made permanent alterations to visual input by creating retinal lesions, a procedure that produces changes in the receptive field properties of cells in the cortex. When this area of the cortex is followed over a period of weeks, alterations in the visual topography of the cortex occur, a phenomenon known as cortical plasticity. Dr. Gilbert’s lab found that the long-term changes involve axonal sprouting and synaptogenesis, and the scientists are now studying the underlying molecular mechanisms. These findings have important implications for the mechanism of functional recovery after brain lesions (such as those associated with stroke) and neurodegenerative disease (including adult macular degeneration).
The changes in cortical circuitry and function following lesions of the central nervous system are also likely to be involved in normal experience-dependent changes in cortical circuits. The Gilbert lab is using their findings to also explore the mechanisms of learning, specifically a form of memory known as perceptual learning. They are interested in the contributions of different cortical areas along the visual pathway and are characterizing the functional changes at the level of individual neurons. Their data suggest that the plasticity of receptive field properties is a process that occurs throughout life, from first learning to analyze visual scenes to later encoding information about new different shapes.
The Gilbert lab has shown that the properties of the visual cortex reflect both sensory and behavioral contexts, suggesting that each cortical area is an adaptive processor that runs different programs according to the immediate demands of the perceptual task. Object recognition, for example, involves a countercurrent process of feedforward and feedback interactions. The top-down signal conveys information about attentional locus, perceptual task and object expectation. These results lead to a novel view of cortical processing: rather than having fixed functional properties, adult neurons are dynamically tuned, changing their specificities with varying sensory experience.
Dr. Gilbert and his colleagues combine anatomy at the light and ultrastructural levels with physiology. They use single-cell and optical recording while integrating molecular approaches with the systems level analysis to understand the mechanisms of adult cortical plasticity. They study the circuitry and synaptic mechanisms underlying the dynamic changes in functional properties of cortical cells. In addition, they do electrophysiological recordings to study the more complex properties of cortical cells, their dependence on top-down influences and on early perceptual learning. Finally, in parallel with the physiological studies, they are doing human psychophysics to explore the perceptual consequences of dynamic changes in cortical properties.
CAREER
Dr. Gilbert received his M.D. and Ph.D. from Harvard Medical School in 1977, where he held an academic appointment until he joined Rockefeller University in 1983 as professor and head of laboratory. In 2004, he was named Arthur and Janet Ross Professor. A member of the National Academy of Sciences and the American Academy of Arts and Sciences, he has received numerous awards, including the W. Alden Spencer Award from Columbia University’s College of Physicians and Surgeons.
