Spatial and temporal relations between extracellular neuronal discharges and local field potential oscillations in cat cerebral cortex during natural wake and sleep states.
Alain Destexhe, Diego Contreras and Mircea Steriade

Society for Neuroscience Abstracts 24: 13, 1998.

The electroencephalogram displays various oscillation patterns during wake and sleep states, but the spatial distribution of underlying neuronal events is not known. Multisite local field potentials (LFPs) and multiunits were simultaneously recorded in the cerebral cortex (area 5-7) of awake and naturally sleeping cats. Slow-wave sleep (SWS) was characterized by oscillations in the slow (< 1 Hz) and delta (1-4 Hz) range. Slow-wave complexes consisted in a positivity of depth LFP, associated with neuronal silence, followed by a sharp LFP negativity, correlated with an increase of firing. This pattern was of remarkable spatiotemporal coherence, as silences and increased firing occurred simultaneously in all cells recorded within 7 mm distance in the cortex. During wake and REM sleep periods, single units fired tonically while LFPs displayed faster activities with increased power in gamma frequencies (20-60 Hz). In contrast with the widespread synchronization during SWS, gamma oscillations during REM and wake periods were synchronized only within neighboring electrodes and small time windows (100-500 ms). This local synchrony occurred in an apparent irregular fashion, both spatially and temporally. Brief periods (< 1 s) of gamma activity were also present during SWS between slow-wave complexes. During these brief periods, the spatial and temporal coherence, as well as the relation between units and LFPs were identical to gamma oscillations of wake or REM sleep. These results show that natural SWS in cats is characterized by slow-wave complexes, synchronized over large cortical territories, interleaved with brief periods of gamma oscillations, characterized by local synchrony, and indistinguishable from the sustained gamma oscillations of activated states.

Supported by the Medical Research Council of Canada.