Abstract
Persistent developmental stuttering (PDS) disrupts speech fluency in about 1% of adults. Although many models of speech production assume an intact sensory feedback from the speech organs to the brain, very little is actually known about the integrity of their sensory representation in PDS. Here, we studied somatosensory evoked potentials (SEPs) in adults who stutter (AWS), with the aim of probing the integrity of sensory pathways. In addition, we tested the processing of dual sensory input to address a putative link between stuttering and focal dystonia. In 15 AWS (aged 15–55 years; three females) and 14 matched fluent speaking adults (ANS), we recorded SEPs at C5′ and C6′ induced by stimulating separately or simultaneously the tongue or the cheek at the corner of the mouth. We determined latencies (N13, P19, and N27) and peak-to-peak amplitudes (N13-P19, P19-N27). We divided amplitudes from simultaneous stimulation by the sum of those from separate stimulation. Amplitude ratios did not differ between groups, indicating normal processing of dual sensory input. This does not support a clinical analogy between focal dystonia and persistent stuttering. SEP latencies as a measure of transmission speed in sensory pathways were significantly shorter in stuttering subjects than in fluent speaking participants, however, this might have been related to a trend for a height difference between groups, and was not confirmed in a replication dataset. In summary, we did not find evidence for dystonia-like sensory overflow of tongue representations in AWS.
Highlights
Stuttering is a speech fluency disorder characterized by involuntary repetitions or prolongations of speech sounds, and by speech blocks caused by a transient loss of speech motor control (Bloodstein and Ratner, 2008)
Latencies are shorter in the person who stutters (PWS) than in the persons who do not stutter (PNS), with tongue alone and with simultaneous stimulation
All trigeminal somatosensory evoked potentials (SEPs) components were shortened, and the stimulation threshold reduced in PWS as compared to PNS, but this was not confirmed in a replication study
Summary
Stuttering is a speech fluency disorder characterized by involuntary repetitions or prolongations of speech sounds, and by speech blocks caused by a transient loss of speech motor control (Bloodstein and Ratner, 2008). A deficient inhibitory integration of afferent inputs as shown in dystonia (Tinazzi et al, 2000) might cause a signal overflow in sensorimotor loops, and reducing the strength of feedback might reduce the risk for signal overflow (Alm, 2004). We used this methodology to answer our hypothesis by combining SEP of the cheek with SEP of the tongue, attempting to quantify speech muscle related sensory cortex activation patterns. We expected SEP latencies to be normal in PWS since latency deviations had only been reported for event-related potentials (Beal et al, 2010)
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