Is state-dependent alternation of slow dynamics in central single neurons during sleep present in the rat ventroposterior thalamic nucleus?

Abstract

Based upon our previous results in cats, we hypothesized that neurons in the central processor systems of the brain generally exhibit state-dependent dynamics alternation of slow fluctuations in spontaneous activity during sleep. To test the validity of this hypothesis across species, we recorded single neuronal activity during sleep from the ventroposterior (VP) thalamic nucleus in unanesthetized, head-restrained rats. Spectral analysis was performed on successive spike-counts of neuronal activity recorded during three stages of the sleep-wakefulness cycle: wakefulness (W, n=6), slow-wave sleep (SWS, n=20), and paradoxical sleep (PS, n=32). We found that firing of VP neurons displayed white-noise-like dynamics over the range of 0.04–1.0 Hz during SWS and 1/ f-noise-like dynamics over the same range during PS. We also demonstrated for the first time that the slow dynamics of neuronal activity during quiet wakefulness (but not drowsiness) are white-noise-like. These results suggest that our hypothesis is true across species. During W and SWS, the brain may be considered as under global inhibition. Conversely, PS may represent a state of global disinhibition in the brain, where neuronal activity exhibits 1/ f-noise-like dynamics. Fluctuations observed in living organisms may be involved in essential processes in generation and function of sleep states.