Psychopharmacological and non-pharmacological interventions have inherent limitations in the treatment of neuropsychiatric disorders. The somatic treatment approaches such as modified electroconvulsive therapy (ECT) are associated with risks of anaesthesia and cognitive adverse effects. Therefore, there is a recent surge of interest in newer somatic treatment approaches in psychiatric disorders, which are device-based, circuit-based and which have more focal actions in the key target regions of the brain. Several such approaches are being studied including transcranial magnetic stimulation (TMS) or recurrent transcranial magnetic stimulation (rTMS), transcranial direct current stimulation (tDCS), vagus nerve stimulation (VNS) and deep brain stimulation (DBS). In this chapter, Indian studies using these treatment modalities for various neuropsychiatric disorders have been reviewed.

TMS is a non-invasive tool, which is used for studying cortical functions, and it has therapeutic applications in various neuropsychiatric disorders. It works on the principle of electromagnetic induction, involving a bank of capacitors, which discharges very large current (peak current  ~5,000 A), which rapidly flows through a simple circuit and then through a copper wire coil. This subsequently results in the induction of a brief and pulsed magnetic field (rise time ~0.1 ms, field strength ~2 T), which is perpendicular to the electric current. When the copper coil is held to the head of the subject, this induced magnetic field generates an electrical current, which is parallel to the plane of the coil and of adequate intensity to cause localised depolarisation of superficial, cortical and subcortical neurons, generating a propagating action potential, which is then used to study the various neuronal functions (George et al. 2002). The application of TMS can produce immediate (within seconds) effects, such as quick jerky movements and perception of flashes of light. Different frequencies of TMS have been found to result in divergent intermediate-term (seconds to several minutes) biologic effects. Studies have revealed that repeated stimulation of a single neuron at low frequency produces long lasting inhibition of cell-to-cell communications, which is called as long–term depression (LTD; Bear 1999); conversely, repeated high-frequency stimulation can improve cell-to-cell communication by long–term potentiation (LTP; Malenka and Nicoll 1999). In low-frequency rTMS (or slow rTMS), stimulation of less than 1 Hz is applied for a longer duration (10–15 min), resulting in LTD of cortical neurons, whereas high-frequency rTMS (or fast rTMS) involves greater 1 Hz frequency stimulation for a shorter duration, manifested as neuronal LTP (Wassermann et al. 1996). Long-term (days to weeks) effects have also been observed with TMS administration, reflected as sustained changes in neurotransmitter release, signalling pathways and gene expression (Post and Keck 2001).