Transcranial magnetic stimulation in Clinical Pharmacology

Abstract

Transcranial magnetic stimulation (TMS) is a safe and easy technique for stimulating neurons in the human central nervous system. Studies combining TMS with drugs in healthy subjects and patients have advanced our knowledge of how TMS activates brain circuits and led to new techniques for evaluating the function of specific systems. For example, TMS techniques can detect effects on axon membranes, glutamatergic and GABAergic synapses and the influence of catecholaminergic systems, as well as group differences due to genetic variations in the response to drugs. With this knowledge base, TMS can now be used to explore and compare the effects of drugs on brain systems and may also serve as a surrogate for behavioral responses in clinical trials.

Figures

Fig. 1

The primary current in the stimulating coil induces a parallel and oppositely directed current in the cortex. From reference [1] with permission.

Fig. 2

Schematic representation of the motor cortex output circuit stimulated by TMS.

Fig. 3

Motor evoked potentials from a single suprathreshold TMS pulse (Test alone) and subthreshold (conditioning)-suprathreshold pairs at 3 and 10 ms intervals. Arrows show stimulus artifacts.

Fig. 4

TMS silent period. Arrow shows stimulus artifact.

Fig. 5

Plot of the ratio of the motor evoked potential with vs. without subthreshold conditioning stimulation at interstimulus intervals from 2–10 ms.