WHO:	Michael Froehler , Advisor: Charlie Duffy, M.D., Ph.D.
TOPIC:	Spatial and Temporal Integration for Cognitive Mappingin Cortical Area MST"
ABSTRACT:	Spatial orientation is supported by two parallel systems utilizing allocentric cues and self-movement information, respectively. The allocentric system depends on a cognitive map that links an animal's current position to environmental landmarks. The self-movement system uses heading and path information to update location within the cognitive map, a process known as path integration. The coordinate transformation from heading to position implies a spatiotemporal integration that has not been previously observed in primate brain.  Neurons in the medial superior temporal (MST) area of monkey cerebral cortex participate in the processing of self-movement information by responding selectively to optic flow, the visual motion pattern seen as the observer moves through the environment. I recorded the responses MST neurons during real translational movement on clockwise (CW) and counterclockwise (CC) circular paths through a lighted room. The directional optic flow selectivity of MST neurons resulted in heading selective responses that were the same on both CW and CC paths in 39% of the neurons recorded. But 44% of the neurons only responded to the heading sequence on a particular path of self-movement, responding to just the CW or the CC path. Still other neurons (17%) responded most strongly to a particular place in the room, in spite of opposite headings on the CC and CW paths at that place. Thus, movement through the room revealed three distinct MST response types: heading, path, and place selectivity. I hypothesized that path selectivity results from the temporal integration of heading information, and place responses arise from spatial integration of landmark cues.  I explored the sensory mechanisms of heading, path and place responses. Visual and real movement cues were dissociated by presenting optic flow simulations and translational movement alone and in combination. MST neuronal responses were dominated by optic flow directional selectivity, with little effect of sled movement. Optic flow video simulations evoked heading and path selective responses but not place selective responses. I conclude that vestibular information is unnecessary for heading and path selectivity, and that heading sequences are sufficient for inducing path effects but other cues are needed to support place selectivity.  The spatial cues necessary to support place selectivity were investigated by recording neuronal responses while providing optic flow video simulations with and without object landmark cues. I found that only the stimulus with spatial landmarks evoked place-selective responses, and conclude that spatial landmarks are necessary for location-selective responses in MST neurons.   These and other experiments described in this dissertation have led to the following conclusions: 1) MST neurons respond to heading, path, and place of self-movement. 2) Heading responses depend on the visual stimulus of optic flow. 3) Path selective responses depend on the temporal integration of naturalistic optic flow heading sequences. 3) Place selective responses depend on the spatial location information provided by environment-fixed visual landmarks. I speculate that these unique neuronal response properties reflect the activity of a cortical-hippocampal circuit for spatial orientation. This subdivision of Papez's circuit for navigation likely utilizes path integration to maintain a veridical cognitive map of allocentric space.  ›
WHEN:	12/18/2003 10:00:00 AM
WHERE:	Med Center Upper S-Wing Auditorium

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