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Michelle Schall, Jacob Westerberg, Alexander Maier, Jeffrey Schall, Geoffrey Woodman; Laminar origins of the N2pc index of visual attention in area V4. Journal of Vision 2020;20(11):299. https://doi.org/10.1167/jov.20.11.299.
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Research into mechanisms of visual attention in humans has relied on an event-related potential known as the N2pc, because it indicates where and when attention is allocated. The N2pc was discovered and characterized in humans, and its neuronal generators are uncertain. Several investigators have conjectured that extrastriate visual area V4 can be a generator of the N2pc based on the similarity of patterns of modulation. Our group has been investigating that conjecture. We have established that the N2pc manifests in macaque monkeys performing visual search. We have established that inverse solutions of the N2pc identify a current generator in the vicinity of V4. Now, to determine most directly whether V4 contributes to the generation of the N2pc, we performed laminar recordings of area V4 concurrent with extracranial EEG in macaque monkeys performing visual search for a singleton. A target stimulus (red or green) was presented among several distractors (homogenous green or red) in an array around a central fixation point. Monkeys shifted gaze to the singleton to earn fluid reward. With field potentials recorded across all cortical layers, we calculated current source density (CSD) of net synaptic depolarizations. On a trial-by-trial basis we compared the magnitude of CSD and polarization of the N2pc. Trial-to-trial variability in the synaptic depolarizations of V4 explained a significant amount of variance in the extracranial voltage fluctuations during the N2pc in a layer-specific manner. These results demonstrate for the first time that V4 contributes to the N2pc.
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