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Cory Hussar, Leo Lui, Tatiana Pasternak; Representation of stimulus speed in prefrontal cortex during speed discrimination task. Journal of Vision 2008;8(6):230. doi: 10.1167/8.6.230.
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© ARVO (1962-2015); The Authors (2016-present)
When monkeys perform behavioral tasks requiring discrimination and retention of direction of visual motion, neurons in prefrontal cortex show direction selective activity reminiscent of responses in motion processing area MT (Zaksas and Pasternak, 2006). We now report that during a task requiring discrimination and retention of stimulus speed, over 60% of PFC neurons show a systematic modulation of activity by stimulus speed and that the nature of this modulation point to its bottom-up origin. Speed selective responses of these neurons fit classifications of low-pass, high-pass or band-pass tuning and were also direction selective, characteristics that disappeared when visual motion was not behaviorally relevant. During a subsequent memory delay, speed selectivity persisted, with many neurons showing activity that varied systematically with remembered speed. However, this activity was largely transient, occurring at different times in different cells, and rarely spanning the entire memory delay, resembling previously observed delay activity during the direction discrimination task. During the comparison phase of the task, when the current and remembered speed must be compared, responses were significantly enhanced when the two speeds matched. This enhancement was largely absent when the comparison speeds were similar and not distinguishable to the monkey, reflecting the nature of the comparison mechanism. Interestingly, while responses to the comparison stimulus were not predictive of the monkey's decision, activity immediately after stimulus offset, while the monkey was withholding the response, was predictive of the monkey's choice, suggesting involvement in the process leading to the motor response. These results demonstrate active participation of PFC neurons in the circuitry sub-serving tasks involving discrimination and retention of visual motion. The nature of the representation of direction and speed in PFC point to strong functional links with neurons in area MT.
Supported by EY11749, T32 EY07125, P30 EY01319.
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