How Local Is the Local Field Potential?

SummaryLocal field potentials (LFPs) are of growing importance in neurophysiological investigations. LFPs supplement action potential recordings by indexing activity relevant to EEG, magnetoencephalographic, and hemodynamic (fMRI) signals. Recent reports suggest that LFPs reflect activity within very small domains of several hundred micrometers. We examined this conclusion by comparing LFP, current source density (CSD), and multiunit activity (MUA) signals in macaque auditory cortex. Estimated by frequency tuning bandwidths, these signals' “listening areas” differ systematically with an order of MUA < CSD < LFP. Computational analyses confirm that observed LFPs receive local contributions. Direct measurements indicate passive spread of LFPs to sites more than a centimeter from their origins. These findings appear to be independent of the frequency content of the LFP. Our results challenge the idea that LFP recordings typically integrate over extremely circumscribed local domains. Rather, LFPs appear as a mixture of local potentials with “volume conducted” potentials from distant sites.

► We studied the scale of neural domain indexed by the local field potential (LFP) ► We found that LFPs can index neural domains on a centimeter or greater scale ► First and second spatial derivatives of the LFP can reduce this scale to tens of micrometers ► The analytic value of the LFP can be enhanced by thus varying its spatial scale