The role of the autonomic nervous system in Tourette Syndrome

Abstract

Tourette Syndrome (TS) is a neurodevelopmental disorder, consisting of multiple involuntary movements (motor tics) and one or more vocal (phonic) tics. It affects up to one percent of children worldwide, of whom about one third continue to experience symptoms into adulthood. The central neural mechanisms of tic generation are not clearly understood, however recent neuroimaging investigations suggest impaired cortico-striato-thalamo-cortical activity during motor control. In the current manuscript, we will tackle the relatively under-investigated role of the peripheral autonomic nervous system, and its central influences, on tic activity. There is emerging evidence that both sympathetic and parasympathetic nervous activity influences tic expression. Pharmacological treatments which act on sympathetic tone are often helpful: for example, Clonidine (an alpha-2 adrenoreceptor agonist) is often used as first choice medication for treating TS in children due to its good tolerability profile and potential usefulness for co-morbid attention-deficit and hyperactivity disorder. Clonidine suppresses sympathetic activity, reducing the triggering of motor tics. A general elevation of sympathetic tone is reported in patients with TS compared to healthy people, however this observation may reflect transient responses coupled to tic activity. Thus, the presence of autonomic impairments in patients with TS remains unclear. Effect of autonomic afferent input to cortico-striato-thalamo-cortical circuit will be discussed schematically. We additionally review how TS is affected by modulation of central autonomic control through biofeedback and Vagus Nerve Stimulation (VNS). Biofeedback training can enable a patient to gain voluntary control over covert physiological responses by making these responses explicit. Electrodermal biofeedback training to elicit a reduction in sympathetic tone has a demonstrated association with reduced tic frequency. VNS, achieved through an implanted device that gives pulsatile electrical stimulation to the vagus nerve, directly modulates afferent interoceptive signals. The potential efficacy of biofeedback/VNS in TS and the implications for understanding the underlying neural mechanisms of tics will be discussed.

Morphology of subcortical brain nuclei is associated with autonomic function in healthy humans

“…However, the ACC has been associated with many processes (see http://neurosynth.org/analyses/terms/acc/) and, therefore, its role in modulating PNS function is unlikely to be specific [Yarkoni et al, ]. Subcortical brain regions are also implicated in modulating PNS function, and the amygdala and pallidum have both previously been associated with core parasympathetic tone, albeit for disparate autonomic functions including metabolism, reward, emotion and motor response [Allen et al, ; Critchley, ; Critchley and Harrison, ; Hawksley et al, ; Macefield, ; McDougall et al, ; Novac and Bota, ; Park and Thayer, ; Su et al, ; Tanaka et al, ]. We have demonstrated that the amygdala and pallidum differ in shape depending on an individual's resting CVT.…”

Pathophysiology of tic disorders

“…83 Thus, the pathophysiology of tic fluctuations may comprise of a dopaminergic modulation of the basic impairment of the CBG loop. Another line of evidence links the modulation of tics with different states of arousal, leading the idea that tics can be suppressed by reducing sympathetic autonomic arousal, 84,85 which is regulated by the noradrenergic system. 86 Along these lines, both a2 noradrenergic agonists and the D2 dopaminergic antagonist are used to treat motor tics.…”

Behavioral therapy for Tourette syndrome and chronic tic disorders

“…Autonomic modulation might therefore have an influence on CNS function and tic occurrence. 44 Neurofeedback is a noninvasive method of autonomic modulation that is based on operant conditioning. It displays real-time physiologic processes such as brain activity, heart rate, or electrodermal activity and by using relevant feedback directs patients how to modulate their physiologic responses.…”