Wednesday, November 28, 2007

Seminar Announcement: Tatiana Pasternak

Prof. Tatiana Pasternak
Department of Neurobiology and Anatomy
University of Rochester Medical Center

Remembering Visual Motion: Cortical Mechanisms

If you are interested in meeting with Prof. Pasternak during her visit, please contact Jayne at

Date: Monday, December 3rd
Time: 4:00 pm
Place: SSPA 2112


The work in my lab is aimed at examining the circuitry sub-serving behavioral tasks requiring processing and retaining sensory information. The focus is on the link between cortical areas traditionally associated with processing of visual motion and regions identified with cognitive control of visually guided behaviors. In this talk I will focus on two cortical regions, motion-processing area MT and on prefrontal cortex (PFC) strongly associated with cognitive control. I will present evidence that neurons in both areas actively participate in tasks requiring discrimination, retention and retrieval/comparison of visual motion, and thus, likely to place demands on both sets of neurons. We recorded activity of neurons in MT and in PFC while the monkeys compared the direction or speed of two random-dot stimuli, sample and test, separated by a memory delay. Many PFC neurons showed robust direction selective and speed selective responses to behaviorally relevant motion, most likely originating in MT. Although during the memory delay there were reliable DS signals in both areas, these signals were largely transient, suggesting that individual neurons in neither area carry sustained memory related signals. Such signals, however, appear to be represented at the population level, with 10-30% of neurons representing remembered motion throughout the memory delay. In both areas responses to the test reflect access to the preceding sample direction or speed. This activity arose earlier in MT, suggesting a role in the comparison to the remembered direction. Only in PFC this effect was predictive of the forthcoming decision. These results illustrate unique contributions of MT and PFC neurons to the task. PFC neurons faithfully reflect task-related information about visual motion, and represent decisions that may be based, in part, on MT's comparison between the remembered sample and test.

Relevant papers:

Zaksas D, Pasternak T (2006) Directional Signals in the Prefrontal Cortex and in Area MT during a Working Memory for Visual Motion Task. J Neuroscience 26:11726-11742.

Pasternak T, Greenlee M (2005) Working Memory in Primate Sensory Systems. Nature Reviews Neuroscience 6:97-107.

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