My laboratory conducts research on how the brain converts sensory inputs into appropriate signals to generate motor behavior. A sensory input from the environment--it might be an auditory input, a visual input or some other sensory event-- is received by the brain. The brain must process this sensory input, decide if it is salient, and then generate an appropriate motor response. With neurophysiological techniques it has been possible to study and understand, at least to some degree, how the sensory inputs are processed by the nervous system and how the motor outputs to the muscles are generated. The organization of the processes in between, which are called sensori-motor integration by neuroscientists, has been much harder to study and understand.

In general it has been found that, at the level of the sensory system input, signals exist in a distributed fashion with spatial coding. For instance, the location of a tactile stimulus on the hand activates a large number of sensory neurons centered at a specific location in the primary somatosensory cortex. If the location of the stimulus changes, the temporal pattern of discharge remains the same, but the location of the center of population discharge changes in cortex. Thus, this is called spatial, distributed coding.

In contrast, on the motor side of the nervous system the movement that is made depends primarily upon the temporal pattern of discharge in the output motoneurons. In the example cited above, if one wanted to move a finger tip to the location on the opposite hand of the tactile sensory stimulus, a precise pattern of motoneuron discharge in terms of duration and frequency would be required. These discharge durations and frequencies would change as the location of the stimulus changes, but the same motoneurons would be active. This is called temporal coding.

At the most basic level sensori-motor integration involves a conversion from spatial to temporal coding, i.e., a spatiotemporal transform. Most of my research is involved in uncovering the structural and functional organizations in the nervous system that carry out spatiotemporal transformations. We use the saccadic system as a model system. In this system a visual stimulus falling on an eccentric location in the retina activates populations of cells centered at precise locations in several cortical and subcortical structures. The location in visual space of the stimulus is coded by where this activity is centered in each of these structures. These structures connect indirectly to groups of motoneurons. When a saccadic eye movement to the location of the stimulus is made, specific groups of motoneurons produce a burst of discharge during the movement. It is the duration and frequency of this burst that determines the size of the eye movement.

My laboratory uses a wide variety of techniques to clarify the neural mechanisms that convert spatial coding to temporal coding in this model system.