Evidence of early category-specific semantic processing in the brain: Responses to english action words in auditory odd-ball

Shtyrov, Y., and Pulvermüller, F.
MRC Cognition and Brain Sciences Unit, Cambridge, UK
E-mail: yury.shtyrov@mrc-cbu.cam.ac.uk

We recorded mismatch negativity (MMN), an index of experience-dependent memory traces, to investigate the processing of action-related words in the human brain. We found that:

1. The topography of the mismatch negativity to the action words showed unusual centro-posterior distribution of the responses suggesting that activity was at least in part generated posterior to usually observed frontal MMNs.

2. MMN responses to the hand-related word stimulus (pick) had a more spread-out lateral distribution, whereas the leg-related stimulus (kick) elicited a more focal dorsal negativity. These differences, remarkably reminiscent of the sensorimotor cortex somatotopy, were confirmed by the source analysis (L2 minimum-norm current estimates).

3. The latency of these word-specific MMN responses was in the range of 140-180 ms and could possibly be related to the recognition of the individual words.

The present results are best explained in terms of distributed neuronal assemblies which function as category-specific memory traces for words and might involve sensorimotor cortical structures for encoding action words. The observed effects occured early in time suggesting that semantic processing may commence in the brain as early as ~140ms after the word onset.