A PET study of the neural systems of stuttering

Abstract

The cause of stuttering is unknown. Failure to develop left-hemispheric dominance for speech is a long-standing theory although others implicated the motor system more broadly, often postulating hyperactivity of the right (language nondominant) cerebral hemisphere. As knowledge of motor circuitry has advanced, theories of stuttering have become more anatomically specific, postulating hyperactivity of premotor cortex, either directly or through connectivity with the thalamus and basal ganglia. Alternative theories target the auditory and speech production systems. By contrasting stuttering with fluent speech using positron emission tomography combined with chorus reading to induce fluency, we found support for each of these hypotheses. Stuttering induced widespread overactivations of the motor system in both cerebrum and cerebellum, with right cerebral dominance. Stuttered reading lacked left-lateralized activations of the auditory system, which are thought to support the self-monitoring of speech, and selectively deactivated a frontal-temporal system implicated in speech production. Induced fluency decreased or eliminated the overactivity in most motor areas, and largely reversed the auditory-system underactivations and the deactivation of the speech production system. Thus stuttering is a disorder affecting the multiple neural systems used for speaking.

The neural substrates for atypical planning and execution of word production in stuttering

“…First, previous research identified the overactivation of the right cerebellum as a neural signature of stuttering (Brown et al, 2005) and as specific to stuttered speech (Braun et al, 1997;Fox et al, 1996). Although the participants in this study produced fluent speech during the experiment, we also found overactivation in the right cerebllum.…”

“…Correspondingly, we also found an additional backprojection from the left PMA to the right cerebellum among stuttering speakers, which was absent among non-stuttering controls. This backprojection may be closely related to the widely reported overactivation of the right cerebellum in stuttering speakers (e.g., Braun et al, 1997;Fox et al, 1996;Ingham et al, 2000). The alteration in the cerebellum-PMA circuit indicates that when producting rapid rhythmic speech, the motor cortex of stuttering speakers may be out-ofcontrol even when the linguistic plan is intact.…”

Neural Correlates of the Lombard Effect in Primate Auditory Cortex

“…Problems with the auditory cortex and vocal feedback processing have been suggested to underlie stuttering in some patients (Timmons and Boudreau, 1972;Fox et al, 1996). In particular, masking noise has been shown to reduce stuttering (Maraist and Hutton, 1957), possibly due to the blockade of vocal feedback during speech.…”

Sensory feedback control of mammalian vocalizations

“…Yet while considerable progress has been made towards identifying regions of the cerebral cortex involved in speech motor control [43,60,88], there is a paucity of details concerning how sensory cues are physiologically integrated into the vocal motor pathways within the cortex. There are some significant differences in brain architecture and activity patterns between stutterers and non-stutterers, particularly in speech and language sensorimotor regions of the cortex [31,32,55], but whether or not these large scale differences ultimately unmask greater insight into sensory feedback control of speech remains to be seen.…”