Stochastic Resonance Modulates Neural Synchronization within and between Cortical Sources

Neural synchronization is a mechanism whereby functionally specific brain regions establish transient networks for perception, cognition, and action. Direct addition of weak noise (fast random fluctuations) to various neural systems enhances synchronization through the mechanism of stochastic resonance (SR). Moreover, SR also occurs in human perception, cognition, and action. Perception, cognition, and action are closely correlated with, and may depend upon, synchronized oscillations within specialized brain networks. We tested the hypothesis that SR-mediated neural synchronization occurs within and between functionally relevant brain areas and thus could be responsible for behavioral SR. We measured the 40-Hz transient response of the human auditory cortex to brief pure tones. This response arises when the ongoing, random-phase, 40-Hz activity of a group of tuned neurons in the auditory cortex becomes synchronized in response to the onset of an above-threshold sound at its “preferred” frequency. We presented a stream of near-threshold standard sounds in various levels of added broadband noise and measured subjects' 40-Hz response to the standards in a deviant-detection paradigm using high-density EEG. We used independent component analysis and dipole fitting to locate neural sources of the 40-Hz response in bilateral auditory cortex, left posterior cingulate cortex and left superior frontal gyrus. We found that added noise enhanced the 40-Hz response in all these areas. Moreover, added noise also increased the synchronization between these regions in alpha and gamma frequency bands both during and after the 40-Hz response. Our results demonstrate neural SR in several functionally specific brain regions, including areas not traditionally thought to contribute to the auditory 40-Hz transient response. In addition, we demonstrated SR in the synchronization between these brain regions. Thus, both intra- and inter-regional synchronization of neural activity are facilitated by the addition of moderate amounts of random noise. Because the noise levels in the brain fluctuate with arousal system activity, particularly across sleep-wake cycles, optimal neural noise levels, and thus SR, could be involved in optimizing the formation of task-relevant brain networks at several scales under normal conditions

Longitudinal effects of botulinum toxin injections on voice-related quality of life (V-RQOL) for patients with adductory spasmodic dysphonia

Adductory spasmodic dysphonia is a focal dystonia of laryngeal muscles. Patients with this disorder typically have severe vocal difficulties, with significant functional, social, and emotional consequences. There is no widely accepted cure for this condition, however, botulinum toxin injections of the thyroarytenoid muscles are considered by most voice clinicians to be the state of the art treatment. Based on extensive experience treating patients for adductory spasmodic dysphonia, we feel that traditional means of voice assessment do not adequately measure either the disease severity or the treatment outcomes. That is, listening to or acoustically analyzing limited phonatory samples does not capture the functional, social, and emotional consequences of this disorder. These consequences will be reflected in a patient's voice-related quality of life (V-RQOL). Using a validated voice outcomes instrument, the V-RQOL Measure, the purpose of this study was to quantify longitudinal changes in the V-RQOL of patients with adductory spasmodic dysphonia who are undergoing botulinum toxin injections. Twenty-seven consecutive new patients presenting with dysphonia to our institution during an 18-month period were diagnosed with adductory spasmodic dysphonia, and treated patients were evaluated prospectively using the V-RQOL Measure. Results indicated that (1) V-RQOL was initially very low for these patients, (2) botulinum toxin injections improved it significantly for each injection cycle studied, and (3) the magnitude of the treatment effect appears to change across injections

Longitudinal effects of botox injections on voice-related quality of life (V-RQOL) for patients with adductory spasmodic dysphonia (part II)

Objective: To investigate the longitudinal effects of botulinum toxin type A (Botox) injections on voice-related quality of life (V-RQOL) for patients with adductory spasmodic dysphonia. Design: Prospective study. Setting: Academic tertiary care referral center. Participants: Forty-two patients who presented to our institution with dysphonia and were diagnosed as having adductory spasmodic dysphonia during a 38-month period. Intervention: Patients received Botox injections into both thyroarytenoid muscles via the cricothyroid membrane. The typical starting dose was 1.0 U per vocal fold. If necessary, the dosage was adjusted in subsequent injections to reduce adverse effects or to enhance duration of benefit. Main Outcome Measures: Patients filled out questionnaires, including the V-RQOL Measure and a selfassessed overall voice rating, before each injection. Postinjection questionnaires were completed 6 to 8 weeks after each treatment. Mean pretreatment and posttreatment scores were calculated for each treatment. Results: The number of treatments per patient ranged from 1 to 7. Statistically significant improvements in mean total and domain V-RQOL scores were calculated for every injection (P.01) (no postinjection questionnaires were available for the seventh injections). The magnitude of the effect remained constant for later injections. Eighty-two percent of the population recorded at least 1 category of improvement in overall self-assessed voice rating with each injection. Conclusions: Botox has a significant beneficial effect on V-RQOL for at least 6 injection cycles. This study demonstrates the efficacy of Botox for treating patients with adductory spasmodic dysphonia and further illustrates the usefulness and validity of the V-RQOL Measure in evaluating patients with dysphonia