Attention in the temporal domain impacts behavioral responses leading to faster response times. Human studies have shown that expectation of an impending behavioral response is reflected in progressively shorter reaction times with increasing trial duration. In this ongoing series of experiments conducted in awake, behaving monkeys we are investigating whether neurons in early visual pathway signal impending events in time that require a behavioral response. The behavioral task required monkeys to maintain fixation on a central spot while attentively tracking a peripherally presented spot for a variable period at the end of which the attention spot disappeared. The monkey had to release a lever within a fixed time window to earn reward. The timing of attention spot disappearance was varied between 900ms to 2300ms, with equal probability over entire time window. However, the conditional probability increased with trial duration. The visual stimulus consisted of two identical patches of sinusoidal gratings of rapidly changing orientations, one of which was centered at the RF of the neuron, and other on the contralateral side. We have previously shown that V1 neuron responses in monkeys performing a temporal attention task exhibit late modulation that starts to ramp up between 150-200ms before the monkeys’ behavioral response and its magnitude increases with the trial duration. Furthermore, the time course of neuronal modulation showed significant negative correlation with their response time. Here we extend our investigations by simultaneously recording neuronal spike response and local field potentials in areas V1 and V4 in two macaque monkeys. Neurons in V4 are known to be robustly modulated by spatial attention that appears early, possibly under fronto-parietal influence, whereas V1 responses only show modest attentional modulation that usually follow attentional changes in V4. We wanted to know if temporal attention followed similar temporal dynamics such that the change in responses with expectation of a behavioral response would arrive earlier in V4 and V1 would follow suit. The analysis of time course of attentional modulation did show a late modulation in V1 and V4 that ramped up before the monkey’s impending behavioral response. However, contrary to our expectation, the modulatory influences arrived earlier in V1, roughly 50-80 ms before those seen in V4. Our results indicate that neurons in V1 and V4 signal behavioral expectations that are expressed through gating of top down attentional processes, but unlike spatial attention, these influences exhibit distinct temporal dynamics that suggests involvement of distinct neuronal networks.

Society for Neuroscience Abstract, 2009.