Hippocampus responds to auditory change in rabbits.

Any change or novelty in the auditory environment is potentially important for survival. The cortex has been implicated in the detection of auditory change whereas the hippocampus has been associated with the detection of auditory novelty. Local field potentials (LFPs) were recorded from the CA1 area of the hippocampus in waking rabbits. In the oddball condition, a rare tone of one frequency (deviant) randomly replaced a repeated tone of another frequency (standard). In the equal-probability condition, the standard was replaced by a set of tones of nine different frequencies in order to remove the repetitive auditory background of the deviant (now labelled as control-deviant) while preserving its temporal probability. In the oddball condition, evoked potentials at 36-80 ms post-stimulus were found to have greater amplitude towards negative polarity for the deviant relative to the standard. No significant differences in response amplitudes were observed between the control-deviant and the standard. These findings suggest that the hippocampus plays a role in auditory change detection.