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

Ragert P, Kalisch T, Bliem B, Franzkowiak S, Dinse HR - BMC Neurosci (2008)

Bottom Line: T-HFS-effects were stable for at least 24 hours whereas t-LFS-induced changes recovered faster.No changes were observed when the stimulated area was very small (< 1 mm2) indicating special requirements for spatial summation.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute for Neuroinformatics, Department of Theoretical Biology, Experimental Neurobiology Lab, Ruhr-University, 44780 Bochum, Germany. patrick.ragert@uni-duesseldorf.de

ABSTRACT

Background: 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.

Results: 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 mm2 on 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.

Conclusion: 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.

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Related in: MedlinePlus

Psychometric functions (regression curves) illustrating the differential effect of 20 min large-field t-HFS and t-LFS stimulation in two representative subjects. Correct responses in percent are plotted as a function of separation distance. 50% level of correct responses is indicated together with resulting thresholds (dashed horizontal and vertical lines). Dashed grey lines show pre-condition before, solid black lines post-condition immediately after t-HFS or t-LFS. After t-HFS there is a distinct shift in the psychometric functions towards lower separation distances (threshold was reduced from 1.83 to 1.48 mm after t-HFS). After t-LFS we found an analogous shift in the psychometric curve, but towards larger separations (threshold was increased from 1.86 to 2.05 mm after t-LFS
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Figure 1: Psychometric functions (regression curves) illustrating the differential effect of 20 min large-field t-HFS and t-LFS stimulation in two representative subjects. Correct responses in percent are plotted as a function of separation distance. 50% level of correct responses is indicated together with resulting thresholds (dashed horizontal and vertical lines). Dashed grey lines show pre-condition before, solid black lines post-condition immediately after t-HFS or t-LFS. After t-HFS there is a distinct shift in the psychometric functions towards lower separation distances (threshold was reduced from 1.83 to 1.48 mm after t-HFS). After t-LFS we found an analogous shift in the psychometric curve, but towards larger separations (threshold was increased from 1.86 to 2.05 mm after t-LFS

Mentions: During the four initial training sessions (s1–s4 = pre) all subjects achieved a stable baseline of discrimination performance on their right d2 as estimated by repeated measures ANOVA with factor SESSION (F(3,39) = 0.759; p = 0.524; n = 14). After applying t-HFS for 20 minutes discrimination thresholds on the right d2 were reduced. Discrimination thresholds were 1.60 ± 0.08 mm before t-HFS and 1.34 ± 0.09 mm after stimulation resulting in an average gain of tactile performance of 0.25 ± 0.04 mm (rmANOVA pre vs. post: F(1,13) = 33.712; p < 0.0001; see Fig. 1 and 2). Linear correlation analysis (Pearson correlation coefficient) revealed no relation between baseline performance before stimulation was applied (pre-condition) and the individual gain in performance found after 20 min of t-HFS (r = -0.090; p = 0.761; n = 14), indicating that baseline performance is not a predictor for perceptual changes evoked by t-HFS. However, the results demonstrate that tactile discrimination performance can be improved by a short time period of tactile HFS. Analysis of the time course of the recovery of the t-HFS-induced changes demonstrated that the discrimination improvement did not recover to baseline conditions 24 hours after termination of stimulation indicating long-lasting alterations in the individual percept that outlasted the stimulation for 24 hours (rmANOVA pre vs. rec 24 h; F(1,13) = 5.771; p = 0.032). Re-testing one week after t-HFS revealed that discrimination thresholds recovered to conditions found prior to t-HFS (rmANOVA pre vs. 1 week; F(1,13) = 2.577; p = 0.132; see Fig. 2). Calculation of d'prime corroborated the improvement of discrimination performance by showing an increase after t-HFS from 2.14 ± 0.10 (pre) to 2.42 ± 0.09 (post). Values remained high 24 hours after stimulation (2.44 ± 0.09) but returned to baseline after 1 week (2.13 ± 0.10).


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

Ragert P, Kalisch T, Bliem B, Franzkowiak S, Dinse HR - BMC Neurosci (2008)

Psychometric functions (regression curves) illustrating the differential effect of 20 min large-field t-HFS and t-LFS stimulation in two representative subjects. Correct responses in percent are plotted as a function of separation distance. 50% level of correct responses is indicated together with resulting thresholds (dashed horizontal and vertical lines). Dashed grey lines show pre-condition before, solid black lines post-condition immediately after t-HFS or t-LFS. After t-HFS there is a distinct shift in the psychometric functions towards lower separation distances (threshold was reduced from 1.83 to 1.48 mm after t-HFS). After t-LFS we found an analogous shift in the psychometric curve, but towards larger separations (threshold was increased from 1.86 to 2.05 mm after t-LFS
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2244613&req=5

Figure 1: Psychometric functions (regression curves) illustrating the differential effect of 20 min large-field t-HFS and t-LFS stimulation in two representative subjects. Correct responses in percent are plotted as a function of separation distance. 50% level of correct responses is indicated together with resulting thresholds (dashed horizontal and vertical lines). Dashed grey lines show pre-condition before, solid black lines post-condition immediately after t-HFS or t-LFS. After t-HFS there is a distinct shift in the psychometric functions towards lower separation distances (threshold was reduced from 1.83 to 1.48 mm after t-HFS). After t-LFS we found an analogous shift in the psychometric curve, but towards larger separations (threshold was increased from 1.86 to 2.05 mm after t-LFS
Mentions: During the four initial training sessions (s1–s4 = pre) all subjects achieved a stable baseline of discrimination performance on their right d2 as estimated by repeated measures ANOVA with factor SESSION (F(3,39) = 0.759; p = 0.524; n = 14). After applying t-HFS for 20 minutes discrimination thresholds on the right d2 were reduced. Discrimination thresholds were 1.60 ± 0.08 mm before t-HFS and 1.34 ± 0.09 mm after stimulation resulting in an average gain of tactile performance of 0.25 ± 0.04 mm (rmANOVA pre vs. post: F(1,13) = 33.712; p < 0.0001; see Fig. 1 and 2). Linear correlation analysis (Pearson correlation coefficient) revealed no relation between baseline performance before stimulation was applied (pre-condition) and the individual gain in performance found after 20 min of t-HFS (r = -0.090; p = 0.761; n = 14), indicating that baseline performance is not a predictor for perceptual changes evoked by t-HFS. However, the results demonstrate that tactile discrimination performance can be improved by a short time period of tactile HFS. Analysis of the time course of the recovery of the t-HFS-induced changes demonstrated that the discrimination improvement did not recover to baseline conditions 24 hours after termination of stimulation indicating long-lasting alterations in the individual percept that outlasted the stimulation for 24 hours (rmANOVA pre vs. rec 24 h; F(1,13) = 5.771; p = 0.032). Re-testing one week after t-HFS revealed that discrimination thresholds recovered to conditions found prior to t-HFS (rmANOVA pre vs. 1 week; F(1,13) = 2.577; p = 0.132; see Fig. 2). Calculation of d'prime corroborated the improvement of discrimination performance by showing an increase after t-HFS from 2.14 ± 0.10 (pre) to 2.42 ± 0.09 (post). Values remained high 24 hours after stimulation (2.44 ± 0.09) but returned to baseline after 1 week (2.13 ± 0.10).

Bottom Line: T-HFS-effects were stable for at least 24 hours whereas t-LFS-induced changes recovered faster.No changes were observed when the stimulated area was very small (< 1 mm2) indicating special requirements for spatial summation.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute for Neuroinformatics, Department of Theoretical Biology, Experimental Neurobiology Lab, Ruhr-University, 44780 Bochum, Germany. patrick.ragert@uni-duesseldorf.de

ABSTRACT

Background: 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.

Results: 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 mm2 on 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.

Conclusion: 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.

Show MeSH
Related in: MedlinePlus