ERP assessment of functional status in the temporal lobe: examining spatiotemporal correlates of object recognition

We have previously used functional magnetic resonance imaging to assess specific anterolateral temporal regions involved in object recognition, providing a novel technique for evaluating functional status in temporal lobe epilepsy (i.e., a site directed approach). However, a method that combines high temporal resolution with spatial mapping is needed to isolate the specific processes associated with these regions (i.e., a process specific approach). In the current study, we evaluated the cognitive processes associated with object recognition and their relationship to the temporal lobe using high-density event-related potentials (ERPs). N300 and late positive component (LPC) responses were examined using a word-picture matching task, with three factors: congruity (match/mismatch), level of abstraction (basic/superordinate), and object category (natural/artificial). The N300 and LPC were analyzed in terms of their temporal characteristics as well as their spatial characteristics through source analysis. The results showed that the N300 primarily indexed processing of congruity and level of abstraction, whereas the LPC primarily indexed processing of object category. In agreement with previous functional imaging studies, N300 and LPC source analysis results confirmed temporal lobe involvement in object recognition. Importantly, LPC object category differences were detected in the anterior temporal lobe. Individual subject analyses revealed that these anterior temporal lobe differences were reliable--with greater activity for natural objects in 84% of subjects. The findings are discussed in terms of clinical applications that use spatiotemporal ERP differences to evaluate functional status of the temporal lobes.