By Anne L. Foundas, MD
Professor of Neurology, Tulane University Health Sciences Center
At this juncture neuroscientists believe that developmental stuttering is a complex motor speech disorder with a strong genetic link. Based on converging evidence from cognitive-behavioral, genetic, neurophysiological and neuroanatomical studies, we have learned that it is likely that stuttering does not result from one causative factor. Furthermore, there is increasing evidence that biological subtypes may be demonstrable with the potential that different therapies may benefit different biologically specific types of stuttering. In a series of recent studies our research group has focused on the anatomy and functional representation of the auditory system in individuals with developmental stuttering.
It is well established that the dysfluencies observed in individuals who stutter may be reduced under a number of conditions including choral reading and alteredauditory feedback. Delayed auditory feedback (DAF) is a technique that can induce fluency in individuals who stutter and can make fluent individuals dysfluent. The auditory system, at least at the level of auditory input, is involved in these fluency inducing conditions. Thus, there may be a defect at the level of auditory processing that is at least partially reversed with these procedures. One hypothesis is that alterations in the auditory signal under conditions of DAF diminish an auditory perceptual defect in people who stutter. This auditory perceptual defect might be related to anomalous anatomy of auditory temporal cortex.
In a 2001 study we found atypical anatomy in auditory temporal brain regions (planum temporale, PT) in a group of adults with persistent developmental stuttering (PDS). We postulated that his anatomic defect may be functionally relevant, and the results of a recent study suggest that there may be a structure-function relationship. In this study (November 2004, Neurology) we examined a group of adults with PDS and fluent adults. The PT was measured on volumetric MRI brain scans, and subjects were classified as having a typical leftward PT asymmetry (left larger than right) or atypical rightward PT asymmetry. Prose passages were read at baseline, with non-altered feedback (NAF), and with DAF, and fluency was measured in these three conditions. In the adults with PDS and atypical PT anatomy, fluency was improved with DAF. In contrast, the adults with PDS and typical PT anatomy did not improve fluency with DAF. Our results suggest that anomalous PT anatomy may be a neural risk for developmental stuttering in some individuals. It may be that atypical rightward PT anatomy may alter speech feedback, and treatment with DAF might allow these people to compensate.
- Foundas AL, Bollich AB, Corey DM, Hurley M, Heilman KM. Anomalous Anatomy in Adults with Persistent Developmental Stuttering: A Volumetric MRI Study of Cortical Speech-Language Areas. Neurology, 2001 57:207-215.
- Foundas AL, Corey DM, Hurley M, Heilman KM. Anomalous auditory processing in adults with persistent developmental stuttering: Dichotic listening measures of free recall and directed attention Cognitive and Behavioral Neurology. (in press).
- Foundas AL, Bollich AM, Feldman J, Corey DM, Hurley M, Lemen LC, Heilman KM. Aberrant auditory processing and atypical planum temporale in developmental stuttering. Neurology, 2004, 63:1640-1646.