TMS as tool to investigate the effect of pharmacological medications on cortical plasticity

The application of medications with a well-defined mode of action on a neurotransmitter or neuromodulator of the central nervous system (CNS) can be utilized to test the pharmaco-physiological properties of transcranial magnetic stimulation (TMS) on cortical excitability and plasticity. Similarly, a physiologically well-defined TMS measure of cortical excitability may be exploited to study a particular drug's effect at the level of the cerebrum. In this review, we aim to assess the impact of calcium channel blockers, Selective Serotonin Reuptake Inhibitors (SSRIs), and GABAergic agents on cortical excitability and plasticity while concurrently investigating how TMS can enhance this understanding. We will begin by reviewing the basics of neuroplasticity, as explored in animal experimentation, and relate this to our knowledge about neuroplasticity induced in humans by TMS techniques. We will then discuss pharmacological modulation of plasticity in humans. Finally, we will review abnormalities of plasticity inherent to certain neuropsychiatric diseases and discuss how the combination of TMS with pharmacological intervention can augment our knowledge of the pathophysiology of these diseases and guide purposeful treatment.