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Abstract
BackgroundThe timing of action potentials (“spikes”) of cortical neurons has been shown to be aligned to the phase of low-frequency (< 10 Hz) local field potentials (LFPs) in several cortical areas. However, across the areas, this alignment varies and the role of this spike-phase coupling (SPC) in cognitive functions is not well understood.ResultsHere, we propose a role in the coordination of neural activity by selective attention. After refining previous analytical methods for measuring SPC, we show that first, SPC is present along the dorsal processing pathway in macaque visual cortex (area MT); second, spikes occur in falling phases of the low-frequency LFP independent of the location of spatial attention; third, switching spatial attention into the receptive field (RF) of MT neurons decreases this coupling; and finally, the LFP phase causally influences the spikes.ConclusionsHere, we show that spikes are coupled to the phase of low-frequency LFP along the dorsal visual pathway. Our data suggest that attention harnesses this spike-LFP coupling to de-synchronize neurons and thereby enhance the neural representation of the attended stimuli.
Highlights
The timing of action potentials (“spikes”) of cortical neurons has been shown to be aligned to the phase of low-frequency (< 10 Hz) local field potentials (LFPs) in several cortical areas
Three rhesus monkeys were trained to direct their covert spatial attention towards a cued eccentric position on a computer screen while maintaining their gaze on a central fixation point. They were rewarded for reporting a small direction change in the moving random dot pattern (RDP) presented at the cued location while ignoring the other stimuli presented at a location in the opposite visual hemifield
Across all distances between the site pairs, spike-phase coupling (SPC) modulation could be found throughout the frequency bands with center frequencies between 3 and 8 Hz (Fig. 4), similar to Fig. 3, indicating that SPC is modulated within the electrodes as close as 305 μm to as distant as 1220 μm. These results suggest that attention widely suppresses the coupling between spikes and low-frequency LFPs in delta (1– 4 Hz) and theta (4–8 Hz) bands in MT, consistent with the previous findings in other visual areas [39]
Summary
The timing of action potentials (“spikes”) of cortical neurons has been shown to be aligned to the phase of low-frequency (< 10 Hz) local field potentials (LFPs) in several cortical areas. Across the areas, this alignment varies and the role of this spike-phase coupling (SPC) in cognitive functions is not well understood. A large majority of neurons in the area MT of extrastriate primate visual cortex are direction-selective, i.e., they systematically vary their firing rate as a function of the direction of visual motion shown in their receptive fields [1, 2]. The local activity of neural populations creates local field potential, continuous periodic signals across a broad frequency spectrum, in contrast to the binary action potentials (“spikes”) generated by the individual neurons. Converging evidence suggests that when spatial locations, features, or objects are attended, neurons in the visual cortex that represent
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