chapter  4
20 Pages

Oscillatory Local Field Potentials

Although cortical oscillations in the 30-to-70-Hz range are robust and commonly found in local field potential measurements in both cat and monkey visual cortex (Eckhorn, Frien, Bauer, Woelbern, & Kehr, 1993; Gray, König, Engel, & Singer, 1989), they are much less evident in spike trains recorded from behaving monkeys (Bair, Koch, Newsome, & Britten, 1994; Young, Tanaka, & Yamane, 1992). We show that a simple neural network with spiking “units” and a plausible excitatory-inhibitory interconnection scheme can explain this discrepancy. The discharge patterns of single units is highly irregular and the associated single-unit power spectrum flat with a dip at low frequencies, as observed in cortical recordings in the behaving monkey (Bair et al, 1994). However, if the local field potential, defined as the summed spiking activity of all “units” within a particular distance, is computed over an area large enough to include direct inhibitory interactions among cell pairs, a prominent peak around 30-50 Hz becomes visible.