Sensory Systems

BIOGRAPHY

Virtually all information that reaches the cerebral cortex must first pass through the thalamus, and we are interested in how the thalamus relays this information. The thalamus had been viewed as a simple relay, but we now know that it dynamically controls the flow of information to cortex. Many forms of attention and levels of consciousness are reflected in the thalamus by different relay functions. We wish to understand at the cellular and behavioral levels how this works, and we have performed our studies mostly on the lateral geniculate nucleus, which is the thalamic relay to cortex for retinal information. An interesting motivation to this work is the realization that only 5-10% of inputs to geniculate relay cells emanate from retina, so that the vast majority of inputs, from brainstem, cortex, and local GABAergic cells, provide a rich, dynamic, and variably modulation of retinogeniculate transmission. Our approach is multidisciplinary and combines morphological, electrophysiological, pharmacological, and behavioral techniques. The morphology is mostly an EM determination of relevant synaptic circuits, the cellular electrophysiology and pharmacology are studied in an in vitro slice preparation, and the behavioral correlates involve single neuron recording from awake, behaving monkeys.

We are especially interested in how the nonretinal inputs affect relay cell function. They operate largely through the synaptic activation of metabotropic receptors, and this produces a long, slow, sustained postsynaptic potential. Such a sustained change in membrane voltage, in turn, effectively controls various voltage- and time-dependent membrane currents. A particularly important on is a low threshold Ca2+ current known as the T-current, the activation state of which strongly influences the relay of retinal information. Our studies are directed at the cellular level to understand how the various modulator inputs control the T-current. At the behavioral level, we are trying to understand how activation or inactivation of the T-current is related to various behavioral states and levels of attention.