We examined the influence of rapid-rate transcranial magnetic stimulation on heart rate and blood pressure in 13 healthy volunteers. In a first series three different cortical magnetic stimuli were applied: over C3, C4 and Fz (10/20 system), in a second series additionally over Pz. We also used a stimulus over the brachial plexus and a sham stimulus. Five stimuli of each location were applied with a Cadwell high speed magnetic stimulator using a focal point circular coil. Stimulus train duration was 500 ms, stimulus frequency 20 Hz. Stimulus strength was 70–90% of maximum stimulator output, 20% of maximum stimulator output above subjects' individual motor threshold. The subjects assessed stimulus inconvenience immediately after stimulation. ECG and blood pressure (Finapres) were recorded continuously during the 1 h test. In all subjects there was a clearly marked autonomic response with heart rate acceleration and decrease in blood pressure after all stimuli. There was no difference in responses between cortical stimuli. Blood pressure decrease after sham stimulation was significantly smaller than after cortical stimulation, it was more marked after brachial plexus stimulation. Autonomic reaction correlates well with subjective estimation of stimulus inconvenience. We conclude the observed effect of rapid-rate transcranial magnetic stimulation to be associated to rather an unspecific arousal reaction than to a direct stimulation of autonomic cortex areas. We did not observe any clinically relevant side-effects.
The post-imperative negative variation (PINV) comprises a slow negative potential shift extending up to several seconds following a signaled taskrelevant stimulus or response. This slow negativity is particularly intriguing, since it seems to be a component of event-related potentials which is found to be larger in amplitude in schizophrenics than in healthy subjects, whereas typically, amplitudes of such components are reduced in patient groups. In the latter case, differences may be due to higher intra-individual response variability and lower signal-to-noise ratio on the part of the patients. Obviously, such an interpretation cannot explain the PINV results. Furthermore, the occurrence of a PINV seems to be reliably related to the diagnosis of a schizophrenic disorder and other severe psychopathological conditions. It can be elicited repeatedly, and measured, independent of clinical judgment, objectively as well as non-invasively. Although frequently found in schizophrenic patients, the PINV is not a specific signature of schizophrenia but is also found in patients with major depressive disorders, and sometimes also in anxiety disorders [1-3], and in patients with obses-
The central representation of sensory perception relates in an orderly way to the spatial arrangement of receptors in the periphery. The cortical maps of visual space (retinotopy), the body surface (somatotopy), or tone frequency (cochlear place; tontotopy) can be individually determined by means of magnetic source imaging. In a similar manner, it is possible to map motor organization along the central sulcus. Usually, a first major peak of the magnetic field evoked by a sensory stimulus is determined and a single equivalent moving dipole is fitted to the field measured from sensors over the respective primary cortical area. Tactile evoked fields, for instance, show a first major peak around 30-70 ms after stimulus onset. The field pattern of short-latency somatosensory components is fairly dipolar and a single moving dipole is an adequate model to localize the generator of this SEF component in most cases. This generator is located in area 3b contralateral to the stimulated site [1-5].
Braille reading is a behaviorally relevant task, often carried out several hours a day. In blind Braille readers, reorganization of the motor cortex has been demonstrated using transcranial magnetic stimulation (TMS). For instance, the cortical representation of the finger muscles involved in the reading process encompasses an expanded area in the motor cortex (1-3]. Furthermore, in a singlesubject pilot study with a normal sighted person, Rockstroh and coworkers [4] demonstrated that the organization of the primary somatosensory cortex, presumably area 3b, could be changed by Braille training. From these results it can be concluded that Braille reading is a potent behavioral task capable of inducing cortical reorganization, and can therefore serve as a model in investigating use-dependent adaptation of somatosensory cortical representation and related perceptual changes. This task may also be used to study the time-course of cortical adaptation to new demands. This was the major aim of the pilot
