Brain correlates of stuttering and syllable production - A PET performance-correlation analysis

To distinguish the neural systems of normal speech from those of stuttering , PET images of brain blood pow were probed (correlated voxel-wise) with pe r-trial speech-behaviour scores obtained during PET imaging. Two cohorts we re studied: 10 right-handed men who stuttered and 10 right-handed, age- and sex-matched non-stuttering controls. Ninety PET blood flow images were obt ained in each cohort (nine per subject as three trials of each of three con ditions) from which r-value statistical parametric images (SPI{r}) were com puted. Brain correlates of stutter rate and syllable rate showed striking d ifferences in both laterality and sign (i.e. positive or negative correlati ons). Stutter-rate correlates, both positive and negative, were strongly la teralized to the right cerebral and left cerebellar hemispheres. Syllable c orrelates in both cohorts were bilateral, with a bias towards the left cere bral and right cerebellar hemispheres, in keeping with the left-cerebral do minance for language and motor skills typical of right-handed subjects. For both stutters and syllables, the brain regions that were correlated positi vely were those of speech production: the mouth representation in the prima ry motor cortex; the supplementary motor area; the inferior lateral premoto r cortex (Broca's area); the anterior insula; and the cerebellum. The princ ipal difference between syllable-rate and stutter-rate positive correlates was hemispheric laterality. A notable exception to this rule was that cereb ellar positive correlates for syllable rate were far more extensive in the stuttering cohort than in the control cohort, which suggests a specific rol e for the cerebellum in enabling fluent utterances in persons who stutter. Stutters were negatively correlated with right-cerebral regions (superior a nd middle temporal gyrus) associated with auditory perception and processin g, regions which were positively correlated with syllables in both the stut tering and control cohorts. These findings support long-held theories that the brain correlates of stuttering are the speech-motor regions of the non- dominant (right) cerebral hemisphere, and extend this theory to include the non-dominant (left) cerebellar hemisphere. The present findings also indic ate a specific role of the cerebellum in the fluent utterances of persons w ho stutter. Support is also offered for theories that implicate auditory pr ocessing problems in stuttering.