Variability and interdependence of local field potentials: Effects of gainmodulation and nonstationarity

Cortical potentials following sensory stimulation are widely analyzed as th e 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 firs t model, neuronal populations coupled through nonlinear sigmoid functions h ave their effective connectivity modulated by the evoked response. This lea ds to fast changes in the ongoing activity measured by ensemble variance, c ross-correlation, spectral power, or coherence time functions. In the secon d model, trial-to-trial amplitude variability of a stereotyped evoked respo nse leads to similar modulation in ongoing activity. Specific predictions f rom both models are tested against local field potentials recorded intracor tically from monkeys performing a visuomotor task. (C) 2001 Elsevier Scienc e B.V. All rights reserved.