The role of pre-SMA for time-critical speech perception - A transcranial magnetic stimulation (TMS) study

The pre-supplementary motor area (pre-SMA) is engaged in speech comprehension under difficult circumstances such as poor acoustic signal quality, cognitive load, or time-critical conditions. Previous studies found left pre-SMA activated when subjects listen to accelerated speech. Here we tested the functional role of the pre-SMA for accelerated speech comprehension by inducing a transient “virtual lesion” using continuous theta-burst stimulation (cTBS). Participants were tested (1) prior to (pre-baseline), (2) 10 min after (test condition for the cTBS effect), and (3) 60 min after stimulation (post-baseline) using a sentence repetition task (formant-synthesized at rates of 8, 10, 12, 14, and 16 syllables/s). Speech comprehension was quantified by the percentage of syllables in correctly reproduced words. For high speech rates, subjects showed decreased performance in the test conditions as compared to the baselines. This transient suppression of speech comprehension indicates that pre-SMA contributes to time-critical encoding of phonetic-linguistic information.