Friday, February 20, 2004

12 noon

Redwood Neuroscience Institute

Title: The Thalamus as a Relay that Sends Copies of Motor Instructions

to the Cerebral Cortex.

Ray Guillery

Anatomy Department

University of Wisconsin, Madison.

Abstract:

The thalamus is classically seen as a relay on sensory pathways to the cerebral cortex.  Messages coming into the thalamus are thought of as bringing information about internal and external events, so that the thalamus can pass these messages on to cortex for processing and for further passage through a series of higher (sensory) cortical areas, eventually to a motor output.
Recent anatomical studies of pathways to the thalamus present a different view. Some of the inputs to the thalamus are “first order”, coming from visual, auditory, tactile, etc. pathways, or from lower brain centers like the cerebellum or the mamillary bodies.  Others are “higher order” pathways, coming from cerebral cortex and providing trans-thalamic connections for messages to pass from one cortical area to other (higher) cortical areas.  Most, possibly all of these pathways, first and higher order,  into the thalamus are made up of nerve fibers that branch, sending one branch to the thalamus and the other branch to motor or pre-motor centers of the brain stem and spinal cord.   That is, the messages that the thalamus is passing to the cerebral cortex can be seen as not just providing sensory information, but also as providing copies of messages that have already been sent to motor or pre-motor centers.  Some are instructions from receptors, or from lower centers innervated by the receptors, for basic, spinal or bulbar reflexes, whereas others are (probably complex) instructions sent out by higher cortical areas to brain stem and spinal cord.  The close and often puzzling link between action and perception that has produced many thoughtful commentaries in the past can now be considered in the light of these recently defined thalamic links.  To what extent should we see perceptual processes as based upon an analysis of current instructions for action?