Human intracerebral potentials associated with target, novel, and omitted auditory stimuli

We recorded late auditory potentials from lateral and medial regions in the frontal, temporal and parietal lobes of patients with temporal lobe epilepsy implanted with horizontal depth electrodes. Tone sequences were presented in three tasks: 1) auditory target detection in a tone sequence, 2) target detection with interspersed novel stimuli, and 3) detection of stimulus omissions. At frontal sites, potentials to targets showed a triphasic response with peak latencies around 200, 270 and 350 ms. At temporal sites, potentials consisted of a generally positive 285 ms peak which was sometimes accompanied by a negative peak at 200 ms or at 400 ms. At parietal sites, potentials were generally triphasic with latencies of about 230, 300, and 370 ms. At most sites, potentials evoked by novel stimuli had shorter latencies than those evoked by targets. The frontal and parietal potentials were either absent or strongly attenuated during stimulus omissions. The results lend further support to the multiple generator hypothesis of late potentials and suggest that some of the cerebral sources of the late potentials are stimulus dependent while others are not.