A MEG investigation of single-word auditory comprehension in aphasia.

PURPOSE To explore whether individuals with aphasia exhibit differences in the M350, an electrophysiological marker of lexical activation, compared with healthy controls. METHOD Seven people with aphasia, 9 age-matched controls, and 10 younger controls completed an auditory lexical decision task while cortical activity was recorded with magnetoencephalography. There were 2 stimulus conditions of interest: identity primed (i.e., a word preceded by itself) and semantic primed (i.e., a word preceded by a semantically related word). Latency and amplitude of the M350 response as well as reaction time were measured. RESULTS Consistent with the age-matched control group, the group with aphasia showed both identity and semantic priming behaviorally. In contrast to the control groups, the group with aphasia did not show either semantic or identity priming of the M350 response. This group also demonstrated longer M350 latencies than either control group. Furthermore, within this group, M350 latency was positively correlated with a measure of semantic impairment. CONCLUSIONS These findings highlight the usefulness of temporally sensitive measures when studying aphasia and demonstrate that the latency of electrophysiological markers is of interest in this population. In particular, increased M350 latency appears to be indicative of a semantic processing impairment.