Introduction

The basic rationale for attempting to use rTMS as a therapeutic tool is that it is known to produce effects on cerebral cortex that outlast the stimulus. The assumption is that, in some cases, it may be possible to manipulate these long-term effects either to reverse the pathological processes responsible for the condition, or to change the excitability of remaining healthy systems so that they can compensate for the underlying disturbance. In this chapter we will consider the use of rTMS in psychiatric conditions and in movement disorders. However, before discussing clinical details, we consider the available data about the long-term effects of rTMS in healthy subjects from the standpoint of designing therapeutic trials on patients. In particular, we ask first whether rTMS can ever be targeted accurately enough at specific neural populations to achieve a therapeutic effect and, second, whether the effects it produces will last long enough to be used as a clinical treatment.

Effect on neural circuits, local

Most of our knowledge about the actions of rTMS comes from studies of the motor cortex, although a smaller number of investigations suggest that the basic principles may apply to visual (Boorojerdi et al., 2000) or frontal (Speer et al., 2000) cortex. As summarized in previous chapters, much of this work has described the effects of rTMS in terms of the excitability of the corticospinal output to single pulse TMS.