Neuro-stimulation in Anxiety Disorders: Scopes and Hopes

Volume 6 Issue 7 July, 2016

Over the last century, neuro-stimulation techniques have emerged as important treatment modalities in the management of various neurological and psychiatric disorders. Neuro-stimulation techniques bring therapeutic benefits by modulating the neuronal tissue. Electroconvulsive therapy (ECT) is the oldest neuro-stimulation technique, which was followed by Deep Brain Stimulation (DBS), Vagus Nerve Stimulation (VNS) and transcranial Direct Current Stimulation (tDCS). All the above modalities of neuro-stimulation used electrical stimuli for stimulation brain. Subsequently, research innovations in neuropsychiatry had given birth to magnetic stimulation techniques such as Transcranial Magnetic Stimulation (TMS) and Magnetic Seizure Therapy (MST).

Neuro-stimulation produced by ECT and MST is convulsive in nature, whereas others produce non-convulsive neuro-stimulation. TMS and tDCS can only stimulate the superficial cortical regions, however the stimulation produced by other neuro-stimulation modalities can reach deep seated brain structures (e.g., thalamus and basal ganglia). ECT produces diffuse brain stimulation, whereas others produce focal stimulation of brain areas. Various neuronal circuits connecting cortico-subcortical structures (circuits connecting frontal cortex with limbic system, thalamus and basal ganglia) are involved in processing of emotions, accompanying cognitive elements and the behavioral manifestations. Dysfunction of above circuits are implicated in Anxiety disorders as well as many other psychiatric disorders. Hence, it is essential to identify and target the brain area involved with specific disorders.

In OCD, various neuro-stimulation techniques like DBS, TMS, ECT and tDCS have been studied. DBS of the deep brain structures like – anterior limb of internal capsule, ventral striatum, nucleus accumbens, subthalamic nucleus, inferior thalamic peduncle as well as globus pallidus interna is helpful in ameliorating symptoms of OCD refractory to conventional treatments. In post-traumatic stress disorder (PTSD), hyper-function in amygdala plays a pivotal role in excessive processing of the traumatic memories. DBS targeting amygdala reduces the symptoms of PTSD. tDCS is also found to be effective in PTSD. Low frequency TMS has been found to be effective in reducing anxiety in patients with PTSD by reducing the hyperactivity of right DLPFC. In panic disorder, low frequency TMS over right DLPFC may be helpful in reducing anxiety TMS and tDCS may have some role in reducing anxiety symptoms in patients with generalized anxiety disorder. The therapeutic effects of VNS in reducing the anxiety symptoms is through modulation of specific brain regions like – locus ceruleus, amygdala, hippocampus and orbitofrontal cortex.

Neuro-stimulation techniques in anxiety disorders are emerging trends of therapy. They are in different stages of research. Most of the related studies have small sample sizes, which limit their generalizability. There is a need to keep oneself updated with the evidences and current understandings about neuro-stimulation techniques, otherwise it may lead to under-use or over-use (misuse) of these novel therapeutic modalities.