Transcranial Magnetic Stimulation in Health and Disease

(S u m m a r y) After a historical review of science and technology developments which leads to the invention of transcranial magnetic stimulation (TMS) (Chapter 1) in the next chapter (Chapter 2) the basic information for functional role of motor cortex in motor control is given. An essential part of the book is devoted to the studies of sensorimotor integration using TMS. Sensorimotor integration is the process whereby sensory input is integrated by the central nervous system and used for assisting motor program execution. Motor evoked potentials (MEPs) in response to TMS are subject to various influences. A powerful means to modify MEPs is muscle vibration (MV) (Claus et al., 1988). The vibration stimuli mainly excite the muscle spindle afferents and the motor cortex is primarily responsible for processing of muscle spindle signals and limb movement perception. Muscle vibration in healthy subjects (Chapter 3). In healthy subjects MEPs in the vibrated muscle are augmented when TMS is applied more than 120 ms after MV onset (Fig. I). MEPs recorded from the antagonist of the vibrated muscle are suppressed simultaneously (Siggelkow et al., 1999). The augmentation of the MEPs in the vibrated muscle was observed at MV frequencies 80 and 120 Hz but not at 160 Hz and was increasing with ongoing MV. In contrast, the inhibition in the antagonist revealed a reverse time course and was also induced by vibration frequency 160 Hz. When a transcranial electrical stimulation (TES) was used, MEPs were not augmented in the vibrated muscles while those in the antagonist were decreased (Kossev et al., 1999) (Fig. II). This dissociation between the effects of TMS and TES as well as the different frequency dependencies and different time courses suggest involvement of different neuronal circuits and possibly different receptor inputs in the MEP augmentation. It seems that MEP augmentation in the vibrated muscle is caused by cortical activation while MEP depression in the antagonist involves both spinal and cortical circuits and probably other dynamic mechanoreceptors (Kossev et al., 2001). Транскраниална магнитна стимулация в норма и патология 164 Fig. I. Area of motor evoked potentials (MEPs) recorded from the vibrated extensor carpi radialis muscle (ECR) and its antagonist flexor carpi radialis (FCR). The parameters are normalized to the mean control values and pooled for all subjects (mean ± standard error; n = 10). MEPs were recorded without muscle vibration (control – c.), 0.5 s and 3 …