Advent of rTMS as a neuromodulatory approach for managing neuropsychiatric conditions

Volume 6 Issue 3 March 2016

Despite the considerable research on neuropsychiatric disorders over the past years, the understanding of the biological basis of these disabling disorders is still fragmentary. The effect of pharmacological intervention has pointed out role of specific neurotransmitter systems of etiological importance, but many symptoms in such disorders still do not respond to pharmacotherapy adequately. More recently brain imaging investigations, like Positron Emission Tomography (PET) and functional Magnetic Resonance Imaging (fMRI), have identified multiple structural and functional abnormalities, including changes in networks of brain regions.

Since its commercial advent in 1985, transcranial magnetic stimulation (TMS), a technique for stimulating neurons in the cerebral cortex through the scalp, safely and with minimal discomfort, has captured the imaginations of scientists, clinicians and lay observers. Initially, a laboratory tool for neurophysiologists studying the human motor system, TMS now has a growing list of applications in clinical and basic neuroscience. TMS is based on Faraday’s principle of electromagnetic induction and features the application of rapidly changing magnetic fields to the scalp via a copper wire coil connected to a magnetic stimulator. These brief pulsed magnetic fields of 1-4 Tesla pass through the skull and create electric currents in discrete brain regions. The currents induced in the brain can be of sufficient magnitude to depolarize a population of neurons and evoke a certain phenomenon. Repetitive trains of TMS (rTMS) applied to targeted brain regions can suppress or facilitate cortical processes, depending upon stimulation parameters. In most instances, continuous low frequency (≤1Hz) rTMS decreases the excitability of the underlying cortex while bursts of intermittent high frequency (≥1Hz) enhance it. The fact that the modulatory effects of rTMS can outlast the duration of its application has led to the exploration of the technique as a potential treatment modality with promising results in various neuropsychiatric disorders. The after-effects of rTMS are influenced by the magnitude and duration of stimulation, the level of cortical excitability and the state of activity in the targeted brain region. It exerts its effect by increasing or decreasing the excitability of corticocortical or corticospinal pathways depending on multiple stimulation parameters like intensity, frequency and coil orientation.

In recent years, rTMS has shown some promise in treatment of varied neuropsychiatric disorders like auditory hallucinations, negative symptoms and cognitive functioning in schizophrenia, depressive disorders, obsessive compulsive disorders, Parkinson’s disease, cognitive impairment in stroke and others.

rTMS is an underutilized treatment modality currently, being present at some institutions and in some geographical locations of the world. There is an urgent need to demonstrate its importance to the policymakers and clinicians alike for better use and favourable outcome in patient population.