Hippocampal event-related potentials to tone duration deviance in a passive oddball paradigm in humans

The mismatch negativity (MMN), a component of event-related potentials (ERPs), is assumed to reflect a preattentive auditory discrimination process. Although an involvement of hippocampal structures in deviance detection was shown in animal experiments, invasive recordings in humans have not been able to provide such an evidence so far. In the current study, ERPs were recorded from intrahippocampal and scalp electrodes in 16 epilepsy patients. Stimulation consisted of trains of six tones, with one tone deviating in duration (100 vs. 50 ms). In the rhinal cortex, ERPs elicited by deviants were larger in amplitude than those of standards (around 200 ms). The rhinal activation was succeeded by a long-lasting hippocampal ERP component (around 350 ms). However, in contrast to the rhinal activation, hippocampal activation was also elicited by the 1st stimuli of the train and might, therefore, be related more to salience detection than to deviance detection. The current study provides evidence that the MMN is part of a multistage comparison process and that the rhinal cortex is part of its underlying cortical network.