Abstract
SummaryGrowing evidence suggests that distributed spatial attention may invoke theta (3–9 Hz) rhythmic sampling processes. The neuronal basis of such attentional sampling is, however, not fully understood. Here we show using array recordings in visual cortical area V4 of two awake macaques that presenting separate visual stimuli to the excitatory center and suppressive surround of neuronal receptive fields (RFs) elicits rhythmic multi-unit activity (MUA) at 3–6 Hz. This neuronal rhythm did not depend on small fixational eye movements. In the context of a distributed spatial attention task, during which the monkeys detected a spatially and temporally uncertain target, reaction times (RTs) exhibited similar rhythmic fluctuations. RTs were fast or slow depending on the target occurrence during high or low MUA, resulting in rhythmic MUA-RT cross-correlations at theta frequencies. These findings show that theta rhythmic neuronal activity can arise from competitive RF interactions and that this rhythm may result in rhythmic RTs potentially subserving attentional sampling.
Highlights
Spatial attention can exhibit fluctuations that under some tested conditions might be rhythmic
reaction times (RTs) were fast or slow depending on the target occurrence during high or low multi-unit activity (MUA), resulting in rhythmic MUA-RT cross-correlations at theta frequencies
These findings show that theta rhythmic neuronal activity can arise from competitive receptive fields (RFs) interactions and that this rhythm may result in rhythmic RTs potentially subserving attentional sampling
Summary
Spatial attention can exhibit fluctuations that under some tested conditions might be rhythmic In vision, this is apparent, for example, during overt saccadic exploration of visual scenes, during which periods of fixation tend to occur every $200 ms, i.e., in the slow theta range [1, 2]. Similar rhythmic exploration is sometimes observed during apparent fixation periods when subjects perform fast fixational eye movements (microsaccades; MSs) [1, 3]. Such rhythmic sampling phenomena appear to not be limited to overt behavior but have been discovered in investigations of covert distributed spatial attention, i.e., in the absence of overt eye movements. It appears that the brain might engage a spatial sampling mechanism that operates in the theta range when two or more objects are simultaneously monitored
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