Variability and interdependence of local field potentials: Effects of gain modulation and nonstationarity

Cortical potentials following sensory stimulation are widely analyzed as the linear combination of an invariant evoked response component, time-locked to the stimulus, and an independent, ongoing noise component. We consider two alternative models and compare their predictions with data. In the "rst model, neuronal populations coupled through nonlinear sigmoid functions have their e!ective connectivity modulated by the evoked response. This leads to fast changes in the ongoing activity measured by ensemble variance, cross-correlation, spectral power, or coherence time functions. In the second model, trial-to-trial amplitude variability of a stereotyped evoked response leads to similar modulation in ongoing activity. Speci"c predictions from both models are tested against local "eld potentials recorded intracortically from monkeys performing a visuomotor task. 2001 Elsevier Science B.V. All rights reserved.