Transcranial Magnetic Stimulation (TMS) of the sensorimotor cortex results in suppression of perception of a threshold cutaneous stimulus from the contralateral hand fingers. The ability of TMS to reveal specialized functions of the two hemispheres and the role of different cortical regions in detection of peripheral sensory stimuli are still debated. The aim of this study was to investigate whether TMS is able to detect a lateralized hemispheric specialization in sensory perception of uni- vs bimanual sensory stimuli. Eight subjects participated in experiments. TMS was carried out with a Mag Sum 200 magnetic stimulator using a focal coil. Excitability threshold, defined as the minimal intensity and the scalp site (= hot spot) at which the stimulation caused optimal movement of the contralateral hand muscles was first determined. Then, two scalp sites 4 cm frontal and posterior to the 'hot spot' were stimulated, both at threshold and at 10% above it during finger stimulation. Sensory stimuli were applied to 1, 3i and 5 fingers of each hand with an intensity slightly above subjective threshold for perception and delivered in a random sequence on either hand or bimanually (in this case to homologous digits). TMS followed cutaneous stimulation at two intervals of 20 and 40 msec; control conditions (that is finger stimuli without TMS interference or viceversa) were randomly intermingled with test conditions. This psychophysical procedure was repeated for each of the two hemispheres and 45 stimulus pairs were collected. Results show that TMS over the two hemispheres impairs both perception and digit localization of cutaneous stimuli delivered to the fingers of the contralateral hand. Maximal interference occurs when fingers are stimulated 40 msec before TMS, mostly of the right parietal cortex, the mean percentage of errors following stimulation of this site is significantly higher both for uni- and bimanual stimuli. These data suggest a prevalence of the right sensorimotor cortex representation in the human brain. Possible implications to the interpretation of neglect disturbances are discussed.
|Number of pages||1|
|Journal||Italian Journal of Neurological Sciences|
|Publication status||Published - 1997|
ASJC Scopus subject areas
- Clinical Neurology