Presented at the Computation and Systems Neuroscience (COSYNE) Conference 2012
We have recently shown that neurons in the motion processing area MT and in the prefrontal cortex (PFC) are actively engaged in all stages of a task in which monkeys compare two directions of motion, S1 and S2, separated by a delay. Neurons in both areas showed direction selective responses, were active during the delay, and showed comparison effects that correlated with perceptual decision. In the PFC, this engagement was also reflected in trial-to-trial variability of spiking activity (Fano Factor, FF) of putative pyramidal neurons, a likely source of top-down influences on MT. The FF tracked consecutive task components and was predictive of the upcoming neuronal events, dropping with stimulus onset, decreasing prior to salient events and flagging neurons participating in sensory comparisons. Here, we report that the variability of spiking activity in MT during the same behavioral task followed a similar pattern. The FF showed a typical rapid drop with stimulus onset, which was present even for stimuli that appeared remotely from the neuron’s receptive field, revealing that even in the absence of overt activity MT neurons were engaged in discrimination. The FF also reflected stimulus identity during several trial components, even in the absence of selective spiking activity. With time in delay, variability of many neurons increased, the pattern opposite to that observed in PFC, suggesting possible interactions between the two areas in preparation for comparison stimulus. Towards the end of the delay, variability of neurons with future comparison effects decreased, an effect analogous but delayed relative to that observed in the PFC, suggesting its possible top-down influences on MT neurons participating in sensory comparisons. Our results demonstrate that the FF provides a sensitive measure of the engagement of MT neurons in motion discrimination tasks and suggest the nature of their interactions with PFC during such tasks.