Local field potentials primarily reflect inhibitory neuron activity in human and monkey cortex.
Bartosz Telenczuk, Nima Dehghani, Michel Le Van Quyen, Eric Halgren, Syd S. Cash, Nicho G. Hatsopoulos and Alain Destexhe.

Nature Scientific Reports 7: 40211 (2017).

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The local field potential (LFP) is generated by large populations of neurons, but unitary contribution of spiking neurons to LFP is not well characterized. In multielectrode array recordings from human and monkey neocortex, we investigated this contribution by examining the spike-triggered LFP average (st-LFP). The resulting st-LFPs were dominated by broad spatio-temporal components due to ongoing activity, synaptic inputs and recurrent connectivity. We used spatial filtering to reduce the spatial reach of the local field related to a single spike. The filtered st-LFPs were limited to the perimeter of 800 um around the neuron, and propagated at axonal speed, which is consistent with their unitary nature. In addition, we discriminated between putative inhibitory and excitatory neurons and found that the inhibitory st-LFP peaked at shorter latencies, consistently with previous findings in hippocampal slices. Thus, in human and monkey neocortex, the LFP may primarily reflect inhibitory neuron activity.