EEG activation patterns in the frontal lobes of stutterers and nonstutterers during working memory tasks
Baird, Brenda Ratcliff
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Developmental stuttering is a physiological disorder of speech motor control. Unlike acquired conditions, developmental stuttering is responsive to fluency-inducing conditions involving the manipulation or elimination of auditory feedback. It was hypothesized that stutterers experience interference effects from competing sensory feedback during the working memory interval in which contextual information is held on-line in order to prepare subsequent motor responses. Behavior and EEG activity of stutterers and non stutterers were compared during working memory tasks. Participants were 22 male, right-handed stutterers, mean age 28.2 years, age matched with 22 male, right-handed nonstutterers. Behavioral measures included a written verbal fluency task, an auditory delayed match-to-sample key press task, and a written digit span task. As hypothesized, there were no group differences in verbal fluency. Also as hypothesized, stutterers had higher error scores (more false positives) on the auditory delayed match-to-sample key press task. This suggests increased sensitivity to auditory stimuli and difficulty inhibiting response to stimulation. Groups did not differ in digit span, but there was a trend toward significance (p=.07). If stutterers do experience overlapping or excessive sensory stimulation during the working memory phase of speech motor plan assembly, the EEG of stutterers should evidence differences consistent with excessive or inefficient processing of "extra" sensory stimuli. Monopolar recordings were collected from 19 sites in accordance with the international 10-20 system of electrode placement. EEG was recorded during 60 seconds of resting-eyes-closed and resting-eyes-open~ 60 seconds during a silent backwards-subtraction math task; 120 seconds during an auditory delayed match-to-sample key press task. As hypothesized, stutterers exhibited more theta activity than nonstutterers in frontal regions in all conditions, both in the low theta subband (3-5 Hz) and the high theta subband (5.5-7.5 Hz). Also as hypothesized, stutterers produced more alpha activity in the low alpha subband (8-10 Hz) in frontal regions in all conditions. There were no group differences in the high alpha subband (10.5-13 Hz). There were no hemispheric differences in frontal regions. Increased cortical activity and inl;;reased sensitivity to stimuli support the proposed hypothesis that stutterers experience excess sensory stimulation while attempting motor plan assembly, suggestive of stuttering as a disorder of attention.
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