Cortical mechanisms of memory, attention, and spatial representation in primates.
Professor Colby's research is on neural mechanisms of spatial cognition. This is an appealing problem for two reasons. First, it encompasses a wide range of cognitive processes, including perception, attention, working memory, and the generation of action. Each of these cognitive processes contributes to the construction of internal representations of space. Second, spatial cognition is a faculty shared by humans and nonhuman primates and can be usefully studied in each. In humans, functional imaging techniques are used to observe sites of cortical activation during visuospatial performance. In alert, trained monkeys, recordings from individual cortical neurons reveal the specific aspects of information processing carried out by different types of neurons during spatial tasks.
The goal of the research is to understand how neurons in different cortical areas contribute to constructing the representations of space that are used to generate action. The traditional view is that a single representation of space in parietal cortex is used to generate all kinds of motor responses. Dr. Colby has shown instead that parietal cortex contains multiple representations, each suited for guiding different forms of action. For example, neurons in the ventral intraparietal area (VIP) have both visual and somatosensory responses and contribute to guiding movements of the head and mouth. In contrast, neurons in the lateral intraparietal area (LIP) encode salient spatial locations with respect to where the monkey is looking and contribute to guiding eye movements.
Dr. Colby's research has revealed that there are fundamental parallels between a subject's attention to the environment and neural activity in the parietal cortex. Parietal neurons encode not only the locations of currently present stimuli, but also the locations of anticipated and remembered stimuli. They anticipate sensory events, firing before an eye movement that is expected to bring a visible stimulus into the receptive field. They also remember sensory events, firing when an eye movement brings into the receptive field the location where a stimulus was recently present. The conclusion is that parietal neurons represent the locations of salient stimuli regardless of whether this salience is based on anticipation, perception, or memory. In humans, Dr. Colby's recent functional imaging work has shown that spatial working memory is encoded in a distributed network of cortical areas.
Current new directions for this research include exploring frontal and extrastriate cortical areas in monkeys for additional unique forms of spatial representation and carrying out parallel functional imaging experiments in humans.
Melcher, D. and Colby, C.L. Trans-saccadic perception. Trends Cogn Sci 12(12): 466-73, 2008.
Heiser, L.M., Berman, R.A., Saunders, R.C., and Colby, C.L. Dynamic circuitry for updating spatial representations. II. Physiological evidence for Interhemispheric transfer in area LIP of the split-brain macaque. Journal of Neurophysiology 94(5):3249-58, 2005.
Berman, R.A., Heiser, L.M., Saunders, R.C., and Colby C.L. Dynamic circuitry for updating spatial representations. I. Behavioral evidence for interhemispheric transfer in the split-brain macaque. Journal of Neurophysiology 94(5):3228-48, 2005.
Merriam, E.P., and Colby, C.L. Active vision in parietal and extrastriate cortex. The Neuroscientist 11(5):484-93, 2005.