*3.4.2 Repetitive TMS*

This can be used to induce sustained changes in cortical reactivity that significantly outlasts the stimulation period. Repetitive TMS can either activate or inhibit cortical activity, depending on stimulation frequency. Low-frequency stimulation results in depression of the target brain area, while high-frequency stimulation induces the facilitation of the region. Low frequency (1 Hz) stimulation for a period of approximately 15 minutes induces a transient inhibition of the cortex. The mechanisms behind such inhibition are unclear, although there are similarities to long-term depression-like synaptic plasticity. In contrast, stimulation at frequencies of 10–20 Hz has been shown to increase cortical activation. Newer theta-burst stimulation technique is a high-frequency stimulation paradigm that can produce either inhibitory (if applied continuously) or facilitatory (if applied intermittently) effects. These effects are thought to be predominantly mediated by NMDA receptors as well as by modulation of GABA receptor functions [28]. Repetitive TMS-induced changes in cortical

plasticity can potentially be studied as a marker of brain resilience to neuropathology [29]. It has been demonstrated that individuals with schizophrenia have diminished cortical plasticity as measured by these techniques [26].
