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Daniel Zaksas, Nicholas P. LaMendola, Tatiana Pasternak; Remembered direction modulates responses to visual motion in MT and prefrontal neurons. Journal of Vision 2006;6(6):109. doi: 10.1167/6.6.109.
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© ARVO (1962-2015); The Authors (2016-present)
Neurons in area MT are active during all phases of a task where the monkeys compare the direction of two consecutive 500ms stimuli, sample and test, separated by a memory delay (Bisley et al, 2004). Here, we examined whether the remembered sample direction affects responses during the test and found significant attenuation of these responses when test direction matched that of the remembered sample. This attenuation was present only early (100–200ms) in the response and disappeared when the sample was non-coherent. This modulation by sample coherence may be a reflection of the comparison of test direction with a stored template of the sample. Furthermore, absence of modulation by sample direction later in the response suggests that decision-related signals may be carried by neurons at later stages of processing. To examine this possibility we analyzed responses in prefrontal cortex (PFC) recorded during the same task. Many PFC neurons were direction selective, though this selectivity developed about 40ms later than in MT. PFC responses to the test, like those in MT, were attenuated when its direction matched the sample. However, this attenuation began about 80ms later and persisted through the end of the test. Furthermore, it was present when the remembered sample was non-coherent, suggesting that this activity reflected the decision or upcoming motor response. Similarities in activity in MT and PFC during the test suggest a shared functional pathway, although the differences in temporal dynamics and dependence on sample coherence imply unique roles for both areas in working memory for motion.
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