Inferior temporal stream for word processing with integrated mnemonic function

The participation of the inferior temporal cortex in visual word perception and recognition raises several questions: Is there a directed processing s tream proceeding anteriorly by continuous cortical processing? How fast are words processed within such an inferior temporal stream? Does this stream support implicit or explicit memory? To answer these questions, we analyzed the spatio-temporal relationship of event-related potentials, recorded dir ectly from the inferior temporal cortex in epilepsy patients performing a c ontinuous visual word recognition paradigm. Event-related potentials elicit ed an inferior temporal positivity in a strip along the left collateral sul cus. This potential exhibited a linear (r = 0.74) peak latency progression from posterior to anterior inferior temporal regions (approximate to 15 cm/ sec), indicating a directed, intracortical processing stream. Peak amplitud es and latencies showed reliable old/new effects with smaller amplitudes an d shorter latencies for old as opposed to new words. Although the amplitude -old/new-effect occurred for all repeated words (e.g., implicit memory), th e latency-old/new-effect occurred for correctly recognized old words only ( e.g., explicit recognition). These results seem to dissociate two distinct mnemonic processes. The graded decrease of mean ITP peak amplitudes and lat encies, however, does not allow us to exclude a single trace model as assum ed for explicit recognition memory based on familiarity (Mandler [1980]: Ps ychol Rev 87:252-271). Regardless whether there is a dissociation between i mplicit and explicit memory in inferior temporal cortex or not, our finding s are in accordance with an integrated inferior temporal processing stream for words that performs continuously semantic and mnemonic operations suppo rting both implicit and explicit memory. (C) 2001 Wiley-Liss, Inc.