Neural Correlates of Visual Perception and Visually Guided Behavior
One of the most profoundly important approaches to understanding vision involves identifying neuronal events that are correlated with perceptual events or visually guided behaviors. This is an area of research that has made great headway in the past 20 years and it is an approach that is strongly represented amongst our Center investigators, particularly Tom Albright, Ed Callaway, E.J. Chichilnisky, Sascha du Lac, Sergei Gepshtein, Rich Krauzlis, John Reynolds, and Gene Stoner.
Neuronal Mechanisms of Visual Information Processing
Although much progress has been made in identifying neuronal correlates of vision, we are only beginning to grasp the underlying neuronal computations and the circuits that implement them.
The Salk Institute has been on the forefront of three important approaches to this problem: (1) theoretical/computational neuroscience, (2) fine-scale exploration of circuitry using novel molecular and electrophysiological techniques, and (3) localization of neuronal response properties to specific cell classes. Terry Sejnowski is among the world’s leaders using the former approach; other Center investigators working in this area include Chuck Stevens, Rich Krauzlis, John Reynolds, Tom Albright, Gene Stoner, Sergei Gepshtein and Tanya Sharpee.
The Salk Institute is also home to three pioneering empirical approaches to understanding neuronal circuitry and mechanisms. One of these efforts uses novel molecular/genetic tools that enable fine scale circuit tracing as well as manipulation of specific cellular components of circuit function. This effort, spearheaded by Ed Callaway, includes collaborations with Rich Krauzlis, John Reynolds and Tom Albright to investigate the neuronal mechanisms underlying perceptual properties in visual cortex.
A second approach employed by E.J. Chichilnisky uses high-density microelectrode recording to evaluate neuronal communication and computation in the retina. Finally, John Reynolds has recently taken the approach of using electrophysiological properties (action potential waveform) to classify specific cell types and correlate them with neuronal selectivities. The approach has thus far shed valuable light on the neuronal mechanisms of visual attention, and the technique is certain to have broad applicability in empirical studies of neuronal mechanisms.
Visual System Development and Plasticity
Among the most timely and interesting questions in visual neuroscience are those concerning how the system reaches its mature operational state and how it is continually modified by experience. For many years, one of the Salk Institute’s greatest strengths has been in understanding molecular and cellular factors that control neuronal development and patterning of neuronal connections. Investigators of the Center for the Neurobiology of Vision who are applying these approaches include Dennis O’Leary and Greg Lemke, who have explored the chemical factors that influence axon targeting and the emergence of topographic patterns in the central targets of retinal projections. In addition, Ed Callaway has investigated refinements in cortical circuitry that occur with development.
Once mature, the visual system continues to adapt to environmental changes and behavioral contingencies. The neuronal substrates of these changes have become subjects of study in the Center for the Neurobiology of Vision. For example, Tom Albright has studied neuronal selectivity changes in visual cortex that parallel associative learning; Sascha du Lac has similarly explored the neuronal mechanisms that underlie visual-motor learning. Rich Krauzlis, Terry Sejnowski and Tom Albright have collaborated on studies of learning strategies in control of saccadic eye movements. Tom Albright and Sergei Gepshtein have collaborated on investigations of adaptive changes in neuronal/perceptual sensitivity that follow changes in the statistics of the visual environment.
Pathologies of Visual System Organization and Function
Developmental brain pathologies have long afforded a unique approach to understanding brain structure and function. This approach is represented in the Center for the Neurobiology of Vision by studies of two major congenital disorders of brain development, Williams Syndrome and Autism. Both of these are broad-spectrum perceptual, cognitive and behavioral disorders, and each includes striking visual system dysfunctions. The Williams Syndrome research program at the Salk Institute is headed by Ursula Bellugi, who pioneered neuroscientific investigation of this disorder. Bellugi is currently engaged in quantitative assessment of the visual-spatial anomalies associated with Williams. The Autism research program at the Salk Institute is a much newer endeavor, which is founded on a collaboration between Rich Krauzlis, Terry Sejnowski and Tom Albright. It is well known that autistics suffer from deficits in the ability to detect statistical regularities in their environment. The goal of this program is to systematically explore these deficits in the visual domain and, ultimately, link them to neuronal changes.