Long-range cortical synchronization without concomitant oscillations in the somatosensory system of anesthetized cats

To determine whether neuronal oscillations are essential for long-range cor tical synchronization in the somatosensory system, we characterized the inc idence and response properties of gamma range oscillations (20-80 Hz) among pairs of synchronized neurons in primary (SI) and secondary (SII) somatose nsory cortex. Synchronized SI and SII discharges, which occurred within a 3 msec period, were detected in 13% (80 of 621) of single-unit pairs and 25% (29 of 118) of multiunit pairs. Power spectra derived from the auto-correl ation histograms (ACGs) revealed that similar to 15% of the neurons forming synchronized pairs were characterized by oscillations. Although 24% of the synchronized neuron pairs (19/80) were characterized by oscillations in on e or both neurons, only 1% (1/80) of these pairs displayed oscillations at the same frequency in both neurons. Similar results were observed among pai rs of multiunit responses. When single-trial responses were analyzed, the v ast majority of responses still did not exhibit oscillations in the gamma f requency range. These results suggest that separate populations of cortical neurons can be bound together without being constrained by the phase relat ionships defined by specific oscillatory frequencies.