Sound-induced modulation of hippocampal θ oscillations.

The mechanism of response of hippocampal neurons to a specific feature in sensory stimuli is not fully understood, although the hippocampus is well known to contribute to the formation of episodic memory in the multisensory world. Using in-vivo voltage-clamp recordings from awake mice, we found that sound pulses induced a transient increase in inhibitory, but not excitatory, conductance in hippocampal CA1 pyramidal cells. In local field potentials, sound pulses induced a phase resetting of the θ oscillations, one of the major oscillatory states of the hippocampus. Repetitive sound pulses at 7 Hz (θ rhythm) increased the θ oscillation power, an effect that was abolished by a surgical fimbria-fornix lesion. Thus, tone-induced inhibition is likely of subcortical origin. It may segment hippocampal neural processing and render temporal boundaries in continuously ongoing experiences.