Katja Biermann-Ruben & Riitta Salmelin & Alfons Schnitzler - Right rolandic activation during speech perception in stutterers: a MEG study

The focus of our magnetoencephalographic (MEG) study was to obtain further insight into the neuronal organization of language processing in control subjects as compared with stutterers, who have problems with the expression of fluent language.
   We recorded neuronal activity of 10 male developmental stutterers and 10 male controls while they listened to nouns in order to repeat them, and to sentences in order to either repeat or transform them into passive form.
   Using the evoked responses approach, which focusses on transient and temporally stable main current flows in the brain, both subject groups consistently activated similar regions during the perception of language stimuli: auditory cortex, temporo-parietal cortex, inferior-frontal cortex and sensorimotor cortex. Differences between subject groups emerged in the amount and the timing of activation. In the stutterers the left inferior frontal cortex was activated for a short while from 95 to 145 ms after sentence onset, which was not evident in the controls nor in either group during the word task. In both subject groups, the left sensorimotor area was activated when listening to the speech stimuli, but in the stutterers there was an additional activation of the right sensorimotor area from 315 ms onwards, which was more pronounced in the sentence than word task.
   Activation of areas typically associated with language production was observed here also during speech perception both in controls and stutterers. Previous research on speech production in stutterers has found abnormalities in both the amount and timing of activation in these areas. The present data suggest that activation in the left inferior frontal and right sensorimotor areas in stutterers differs from that in controls also during speech perception.
   These results were complemented by the analysis of oscillatory activity. Both subject groups showed enlarged suppression of sensorimotor oscillatory 20-Hz activation in the phase of word production as compared with preceding auditory word reception, which can be interpreted as more cortical engagement in ongoing processings in the sensorimotor area during speaking. But interestingly, during word reception the suppression was lateralized to the left hemisphere mouth area in controls while it was bilateral in stutterers. During word production both subject groups showed bilateral mouth area 20-Hz suppression.
   The data show that sensorimotor activation occured in both groups during reception and production of language. While it was more pronounced in the left hemisphere in controls, it was distributed to both hemispheres in stutterers. We hypothesize, that activation of the right sensorimotor cortex is involved in the cause of stuttering.