Sleep and wakefulness auditory processing: Cortical units vs. hippocampal theta rhythm

A physiological approach to the understanding of the central nervous system auditory processing during behavior requires taking into account the mechanisms of perception, attention and sleep/wakefulness generation. The correlation of the neuronal discharge with the hippocampal theta rhythm has been described for motor and sensory modalities. In this article we address the question of the relationship between unitary activity in the auditory cortex (AI) and the hippocampal theta rhythm. We observed there is a phase-locking between the cortical units and theta waves that was not present after data "shuffling." It may or may not depend on the power of theta hippocampal field potential. On changing behavioral state, a temporal relationship- phase-locking - was found during wakefulness, slow wave sleep and paradoxical sleep. Besides, this correlation may shift when neurons are acoustically stimulated and the same neuron could show different correlation for the spontaneous and evoked activities. The influence that attention processes exert on hippocampal activity may indicate a point of interaction between those processes and the changes in the pattern of discharge of auditory neurons in sleep and wakefulness. Our results are indicative of a new approach for sensory processing analysis in relation to behavioral states and particularly with sleep.