Lawrence Snyder Research Abstract

Our laboratory studies small circuits underlying cognition in the non-human primate model. Currently, we have projects involving spatial representation, memory and movement; eye-hand and bimanual coordination; and correlation-based functional connectivity. In the past we have worked on topics including effector-selective circuits underlying movement, cognitive switch costs, and neuronal correlates of rewards.

Spatial representation and memory:
How are locations in space are represented in the cerebral cortex, and how those representations are used to guide eye and arm movements. More generally, how is sensory spatial information transformed into commands for movement? And, given a system in which this occurs, how can we analyze that transformation?

Parietal cortex has long been implicated in the transformation of visual sensory information into motor commands. A patient with unilateral parietal damage may ignore objects in one half of the world, clothe only half of their body or eat from only half of their plate. Spatial memory is affected, and there are often motor deficits as well. In order to understand the role of the parietal cortex in representing space and subserving movement, we record from individual neurons in macaque monkeys while they perform complex visuo-motor tasks. The animals are trained to look at and reach for colored spots of light - a monkey video game. We ask how the locations of these spots are represented by neural activity in the brain. What frame of reference is used? Is there a single, generic representation or multiple special purpose representations? How is spatial information from other sensory systems combined with visually-derived information? How does the nature of the task, and what the animal intends to do, affect parietal processing? Is parietal cortex specifically involved in the learning of new sensory-motor mappings? How do rewards affect processing?

Frontal cortex has long been implicated in spatial memory. We have been asking whether those memories are effector-specific or effector-general, and what are the computational principles underlying the actual circuits subserving memory.

Eye-hand and bimanual coordination: We easily combine movements of our two arms and eyes in order to manipulate objects in the world. What circuits are responsible for this coordination? To what extent does each hemisphere control a single arm, with communication across the hemispheres subserving bimanual coordination? What are the patterns of eye movements that accompany arm movements to two different locations, and is there anything special about the circuitry driving those movements?

Correlation-based functional connectivity. Resting state functional connectivity using fMRI has greatly advanced our understanding of brain architecture. We still do not know, however, exactly what drives these correlations in blood oxygen levels and whether the correlations play an important role in cognition. We recently developed oxygen polarography so that we can simultaneously record oxygen across multiple brain networks, LFP and spiking activity. We have learned much about the manifestations of functional connectivity correlation in these modalities, and are begin to put together a mechanistic understaning of these processes.