Pharmacology of TMS measures

This article discusses various aspects of the pharmacology of transcranial magnetic stimulator (TMS) measures. TMS measures reflect axonal, or excitatory or inhibitory synaptic excitability in distinct interneuron circuits. TMS measures can be employed to study the effects of a drug with unknown or multiple modes of action, and hence to determine its main mode of action at the systems level of the motor cortex. TMS experiments can also study acute drug effects that may be different from chronic drug effects. TMS or repetitive TMS may induce changes in endogenous neurotransmitter or neuromodulator systems. This allows for the study of neurotransmission along defined neuronal projections in health and disease. This article describes pharmacological experiments that have characterized the physiology of TMS measures of motor cortical excitability. Pharmacological challenging of TMS measures has opened a broad window into human cortical physiology.