title: Differential effects of tactile high- and low-frequency stimulation on tactile discrimination in human subjects.
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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Institute for Neuroinformatics, Department of Theoretical Biology, Experimental Neurobiology Lab, Ruhr-University, 44780 Bochum, Germany. patrick.ragert@uni-duesseldorf.de
authors.forename: Patrick
authors.initials: P
authors.lastname: Ragert
authors.forename: Tobias
authors.initials: T
authors.lastname: Kalisch
authors.forename: Barbara
authors.initials: B
authors.lastname: Bliem
authors.forename: Stephanie
authors.initials: S
authors.lastname: Franzkowiak
authors.forename: Hubert R
authors.initials: HR
authors.lastname: Dinse
mesh_terms: D000328:Adult; D000344:Afferent Pathways / Q000502:physiology*; D004193:Discrimination Learning / Q000502:physiology*; D005385:Fingers / Q000294:innervation / Q000502:physiology; D006801:Humans; D017774:Long-Term Potentiation / Q000502:physiology; D008465:Mechanoreceptors / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D009483:Neuropsychological Tests; D010812:Physical Stimulation / Q000379:methods; D011601:Psychophysics / Q000379:methods; D011984:Sensory Receptor Cells / Q000502:physiology*; D012684:Sensory Thresholds / Q000502:physiology; D013003:Somatosensory Cortex / Q000502:physiology*; D013997:Time Factors; D014110:Touch / Q000502:physiology*; D014732:Vibration