Novelty Processing Depends on Medial Temporal Lobe Structures

ObjectivesThe goal of the present study was to identify the role of the medial temporal lobe (MTL) in the detection and later processing of novelty stimuli. MethodsTwenty-one epilepsy patients with unilateral MTL resection (10 left-sided; 11 right-sided) performed an adapted visual novelty oddball task. In this task two streams of stimuli were presented on the left and right of fixation while the patients electroencephalogram was measured. Patients responded to infrequent target stimuli, while ignoring frequent standard, and infrequent novel stimuli that could appear either contra- or ipsilateral to the resected side. ResultsNovelty detection, as indexed by the N2 ERP component elicited by novels, was not affected by the MTL resections. Later processing of novels, however, as indexed by the novelty P3 ERP component, was reduced for novels presented contra-versus ipsilateral to the resected side. Target processing, as indexed by the P3b, was unaffected. ConclusionsThe current results suggest that MTL structures play a role in novelty processing, but that the novelty signal may originate from a distinct neural source.