Spontaneous high frequency oscillations (HFO) in the local fi eld potential recorded in the nucleus accumbens (NAc) are typically represented by a small peak in the power spectra in the range of 140–180 Hz. These HFO are known to occur in the awake state, but their distribution over the sleep-wake cycle has not been investigated. To address this issue we fi rstly examined the power of HFO during periods of quiet waking, slow-wave sleep (SWS) and REM sleep. Since the electrophysiological activity during general anesthesia resembles certain features of naturally occurring SWS we went on to examine the effect of pentobarbital, isofl urane or urethane anesthesia on spontaneous and ketamine-induced increases in HFO. We found that the power of spontaneous HFO decreased signifi cantly during periods of SWS with respect to both quiet waking and REM sleep. General anesthetics also reduced the power of spontaneous HFO recorded in the NAc and completely blocked the ketamine-induced increase. These fi ndings suggest that behavioural states where the generation of mental activity is most intense are associated with the presence of HFO in the NAc. In line with this, states which lead to decreased mentation, such as naturally occurring SWS and general anesthesia are associated with reductions in the power of HFO. Together these fi ndings suggest that the presence of HFO may have behaviourally meaningful consequences.
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