Homeostatic metaplasticity in primary somatosensory cortex

• Published in: Klinische Neurophysiologie
• Main Authors: Bliem, B, Müller-Dahlhaus, F, Dinse, H, Ziemann, U
• Format: Conference Proceeding
• Language: English; German
• Published: 08.04.2008
• ISSN: 1434-0275; 1439-4081
• DOI: 10.1055/s-2008-1072873

Introduction: Long-term potentiation (LTP) and long-term depression (LTD) are regulated by homeostatic control mechanisms to maintain synaptic strength in a physiological range. While homeostatic plasticity has been demonstrated in human motor cortex, little is known to which extent it operates in other cortical areas and how it relates to behavior. In this study we tested homeostatic interactions between two stimulation protocols – paired associative stimulation (PAS) and peripheral high frequency stimulation (pHFS) in the human somatosensory system. Methods: PAS employed repeated pairs of electrical stimulation of the right median nerve followed by transcranial magnetic stimulation applied to the left primary somatosensory cortex at an interstimulus interval of individual N20-latency minus 15ms or N20-latency minus 2.5ms to induce LTD- or LTP-like changes, respectively. PAS was followed by pHFS consisting of 20Hz trains of electrical stimulation of the right median nerve. Excitability changes in the somatosensory cortex were assessed using median nerve somatosensory evoked potentials. Additionally, tactile spatial discrimination was tested by the grating orientation task. Results: PAS per se had no significant effect on excitability in somatosensory cortex or on tactile discrimination. The direction of effects induced by subsequent pHFS varied according to the type of the preconditioning PAS protocol: after PAS N20–15 , excitability tended to increase and tactile spatial discrimination threshold decreased. After PAS N20–2.5 , excitability decreased and discrimination thresholds tended to increase. Significance: These interactions demonstrate that homeostatic metaplasticity operates in human somatosensory cortex, controlling both cortical excitability and behavioral skills.