IntroductionImpaired proprioception severely affects the control of gross and fine motor function. However, clinical assessment of proprioceptive deficits and its impact on motor function has been difficult to elucidate. Recent advances in haptic robotic interfaces designed for sensorimotor rehabilitation enabled the use of such devices for the assessment of proprioceptive function.PurposeThis study evaluated the feasibility of a wrist robot system to determine proprioceptive discrimination thresholds for two different DoFs of the wrist. Specifically, we sought to accomplish three aims: first, to establish data validity; second, to show that the system is sensitive to detect small differences in acuity; third, to establish test–retest reliability over repeated testing.MethodologyEleven healthy adult subjects experienced two passive wrist movements and had to verbally indicate which movement had the larger amplitude. Based on a subject’s response data, a psychometric function was fitted and the wrist acuity threshold was established at the 75% correct response level. A subset of five subjects repeated the experimentation three times (T1, T2, and T3) to determine the test–retest reliability.ResultsMean threshold for wrist flexion was 2.15°± 0.43° and 1.52°± 0.36° for abduction. Encoder resolutions were 0.0075°(flexion–extension) and 0.0032°(abduction–adduction). Motor resolutions were 0.2°(flexion–extension) and 0.3°(abduction–adduction). Reliability coefficients were rT2-T1 = 0.986 and rT3-T2 = 0.971.ConclusionWe currently lack established norm data on the proprioceptive acuity of the wrist to establish direct validity. However, the magnitude of our reported thresholds is physiological, plausible, and well in line with available threshold data obtained at the elbow joint. Moreover, system has high resolution and is sensitive enough to detect small differences in acuity. Finally, the system produces reliable data over repeated testing.

Objective: Spasmodic dysphonia (SD) is a debilitating voice/speech disorder without an effective cure. To obtain a better understanding of the underlying cortical neural mechanism of the disease we analyzed electroencephalographic (EEG) signals of people with SD during voice production.Method: Ten SD individuals and 10 healthy volunteers produced 50 vowel vocalization epochs of 2500ms duration. Two EEG features were derived: (1) event-related change in spectral power during vocalization relative to rest, (2) inter-regional spectral coherence.Results: During early vocalization (500-1000ms) the SD group showed significantly larger alpha band spectral power over the left motor cortex. During late vocalization (1000-2500ms) SD patients showed a significantly larger gamma band coherence between left somatosensory and premotor cortical areas. Conclusions:Two atypical patterns of cortical activity characterize the pathophysiology of spasmodic dysphonia during voice production: (1) a reduced movement-related desynchronization of motor cortical networks, (2) an excessively large synchronization between left somatosensory and premotor cortical areas. Significance:The pathophysiology of SD is characterized by an abnormally high synchronous activity within and across cortical neural networks involved in voice production that is mainly lateralized in the left hemisphere.

Spasmodic dysphonia (SD) is an incurable focal dystonia of the larynx that impairs speech and communication. Vibro-tactile stimulation (VTS) alters afferent proprioceptive input to sensorimotor cortex that controls speech. This proof-of-concept study examined the effect of laryngeal VTS on speech quality and cortical activity in 13 SD participants who vocalized the vowel /a/ while receiving VTS for 29 minutes. In response to VTS, 9 participants (69%) exhibited a reduction of voice breaks and/or a meaningful increase in smoothed cepstral peak prominence, an acoustic measure of voice/speech quality. Symptom improvements persisted for 20 minutes past VTS. Application of VTS induced a significant suppression of theta band power over the left somatosensory-motor cortex and a significant rise of gamma rhythm over right somatosensory-motor cortex. Such suppression of theta oscillations is observed in patients with cervical dystonia who apply effective sensory tricks, suggesting that VTS in SD may activate a similar neurophysiological mechanism. Results of this feasibility study indicate that laryngeal VTS modulates neuronal synchronization over sensorimotor cortex, which can induce short-term improvements in voice quality. The effects of long-term VTS and its optimal dosage for treating voice symptoms in SD are still unknown and require further systematic study.

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Background. Cervical dystonia (CD) is a neurological movement disorder characterized by involuntary contractions of the cervical musculature and is known to be associated with proprioceptive dysfunction in dystonic/nondystonic limbs. Objectives. We examined how neck botulinum neurotoxin (BoNT) injection affects wrist proprioception and the corresponding sensorimotor cortical activity in CD. Method. Wrist position sense acuity of the dominant (right) hand was evaluated in 15 CD and 15 control participants. Acuity measures were a psychophysical position sense discrimination threshold (DT; based on passive joint displacement) and joint position matching error (based on active movement). Cortical activity during the motor preparation period of the active joint position matching was examined using electroencephalography. Results. In their symptomatic state, patients demonstrated a significantly higher wrist proprioceptive DT, indicating an abnormal passive wrist position sense. Yet BoNT injections had no significant effect on this threshold. During active joint position matching, errors were significantly larger in patients, but this difference vanished after the administration of BoNT. Motor preparation of active wrist position matching was associated with a significantly higher rise of β-band (13-30 Hz) power over contralateral somatosensory-motor cortical areas in patients. This excessive cortical activity significantly declined post-BoNT. Conclusion. Wrist proprioceptive perception during passive/active movements is abnormal in CD. An excessive rise of premotor/motor cortical β-oscillations during motor planning is associated with this proprioceptive dysfunction. Neck BoNT injections normalized the cortical processing of proprioceptive information from nonsymptomatic limbs, indicating that local injections may affect the central mechanisms of proprioceptive function in CD.