The 5-12 Hz oscillations in the barrel cortex of awake rats--sustained attention during behavioral idling?

5-12 Hz oscillations, observed in cortical LFP of awake rats during quiet immobility, were proposed to be either (i) epileptic events or (ii) physiological alpha-like oscillations, manifesting an idling state of the cortex. We aimed to test this controversy.

We recorded LFP from the barrel cortex of awake Wistar rats, while applying weak tactile (whisker) and stronger arousing (electrical) stimuli.

We observed a mean effect of desynchronization of the 5-12 Hz rhythm by the weak tactile stimulation. Arousal reduced the incidence of the 5-12 Hz oscillations and increased the desynchronizing power of tactile stimuli.

Oscillations that can be disrupted by weak, purely tactile stimulation, and whose incidence is reduced by increased arousal, should be interpreted as a physiological phenomenon typical for behavioral idling while the cerebral cortex maintains sensory sensitivity.

Our results contradict the view that the 5-12 Hz oscillatory activity, often observed in fronto-parietal cortical regions of Wistar rats, represents epileptic discharges. Rather, this activity provides a model for studying the physiology of alpha/mu oscillations.