Differential effects of tactile high- and low-frequency stimulation on tactile discrimination in human subjects

<p>Abstract</p> <p>Background</p> <p>Long-term potentiation (LTP) and long-term depression (LTD) play important roles in mediating activity-dependent changes in synaptic transmission and are believed to be crucial mechanisms underlying learning and cortical plasticity. In human subjects, however, the lack of adequate input stimuli for the induction of LTP and LTD makes it difficult to study directly the impact of such protocols on behavior.</p> <p>Results</p> <p>Using tactile high- and low-frequency stimulation protocols in humans, we explored the potential of such protocols for the induction of perceptual changes. We delivered tactile high-frequency and low-frequency stimuli (t-HFS, t-LFS) to skin sites of approximately 50 mm²on the tip of the index finger. As assessed by 2-point discrimination, we demonstrate that 20 minutes of t-HFS improved tactile discrimination, while t-LFS impaired performance. T-HFS-effects were stable for at least 24 hours whereas t-LFS-induced changes recovered faster. While t-HFS changes were spatially very specific with no changes on the neighboring fingers, impaired tactile performance after t-LFS was also observed on the right middle-finger. A central finding was that for both t-LFS and t-HFS perceptual changes were dependent on the size of the stimulated skin area. No changes were observed when the stimulated area was very small (< 1 mm²) indicating special requirements for spatial summation.</p> <p>Conclusion</p> <p>Our results demonstrate differential effects of such protocols in a frequency specific manner that might be related to LTP- and LTD-like changes in human subjects.</p

Motor-Cortical Interaction in Gilles de la Tourette Syndrome

BACKGROUND: In Gilles de la Tourette syndrome (GTS) increased activation of the primary motor cortex (M1) before and during movement execution followed by increased inhibition after movement termination was reported. The present study aimed at investigating, whether this activation pattern is due to altered functional interaction between motor cortical areas. METHODOLOGY/PRINCIPAL FINDINGS: 10 GTS-patients and 10 control subjects performed a self-paced finger movement task while neuromagnetic brain activity was recorded using Magnetoencephalography (MEG). Cerebro-cerebral coherence as a measure of functional interaction was calculated. During movement preparation and execution coherence between contralateral M1 and supplementary motor area (SMA) was significantly increased at beta-frequency in GTS-patients. After movement termination no significant differences between groups were evident. CONCLUSIONS/SIGNIFICANCE: The present data suggest that increased M1 activation in GTS-patients might be due to increased functional interaction between SMA and M1 most likely reflecting a pathophysiological marker of GTS. The data extend previous findings of motor-cortical alterations in GTS by showing that local activation changes are associated with alterations of functional networks between premotor and primary motor areas. Interestingly enough, alterations were evident during preparation and execution of voluntary movements, which implies a general theme of increased motor-cortical interaction in GTS

Talairach coordinates.

<p>Talairach coordinates.</p

Clinical data.

<p>*no sound in the videotape.</p><p>m = male, f = female; MRVS = total score of Modiefied Rush Videotape Rating Scale, Tic-count: tics per minute on video.</p><p>Total number = all tic counted; relative tic number (%) = all tics related to the respective muscle groups.</p><p>Medication: C = Clonidin, D = Dronabinol, H = Haloperidol, P = Pimozid, S = Sulpirid, T = Tiaprid.</p

Coherence spectra between SMA and M1 of one representative GTS-patient (black) and one control subject (grey).

<p>The arrows mark the peak maxima (A). Mean M1-SMA coherence strength in GTS-patients (black) and healthy control subjects (grey; B). Error bars indicate SEM.</p

Mean localizations of all identified sources for control subjects (left) and GTS-patients (right).

<p>Please note that SPM99 has been used for visualization of mean source localizations only and does not provide any statistical comparison between groups.</p