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

Objective: 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.

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

Results: 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.

Conclusions: 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.

Significance: 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.