Sensorimotor deprivation induces interdependent changes in excitability and plasticity of the human hand motor cortex.
Prolonged limb immobilization deprives sensorimotor cortical areas of an important source of excitatory input, as well as of motor output. Previous work has described effects on motor excitability but it is unclear whether motor plasticity is also influenced. In two groups of eight healthy human subjects, the left hand was immobilized for 8 h to induce sensorimotor deprivation of the cortical representation of the abductor pollicis brevis muscle. We used transcranial magnetic stimulation protocols to evaluate motor excitability with motor-evoked potentials, input-output (IOcurve) and short-latency intracortical inhibition (SICI) recruitment curves, as well as long-term potentiation (LTP)/long-term depression (LTD)-like plasticity with paired-associative stimulation (PAS) of the median nerve and motor cortex using an interstimulus interval of 25 ms (PAS25) or 10 ms (PAS10), respectively, in two sessions at least 7 d apart (baseline and after immobilization). After immobilization, the slope of the IOcurve decreased, and SICI at lower conditioning pulse intensities was reduced. The LTP-like effects of PAS25 and the LTD-like effect of PAS10 were both significantly enhanced. The effects differed among individuals: the more IOslope decreased after immobilization, the greater the increase of PAS25 and the smaller the increase of PAS10 effects. We suggest that sensorimotor deprivation has two effects. It increases the sensitivity to remaining sensory inputs and therefore increases the effectiveness of both PAS protocols. In addition, it reduces neuronal excitability to an individually different level, as reflected in the reduced IOslope and leads to an interdependent modulation of synaptic plasticity as such as it shifts the threshold of LTP/LTD-like plasticity induction.
University College London, Institute of Neurology, London WC1n 3BG, United Kingdom, University of Heidelberg, Medical Faculty Mannheim, Central Institute of Mental Health, 68159 Mannheim, Germany, rosenkranz.karin@gmx.de.
Karin
K
Rosenkranz
University of Mannheim, School of Social Sciences, 68131 Mannheim, Germany, and.
Julia
J
Seibel
University College London, Institute of Neurology, London WC1n 3BG, United Kingdom, Clinical Centre Serbia, Institute of Neurology, 11000 Belgrade, Serbia.
Aleksandra
A
Kacar
University College London, Institute of Neurology, London WC1n 3BG, United Kingdom.
John
J
Rothwell
D000328:Adult; D000704:Analysis of Variance; D001703:Biophysics; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006225:Hand / Q000294:innervation*; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D011930:Reaction Time; D012683:Sensory Deprivation / Q000502:physiology*; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation; D014953:Wrist / Q000294:innervation; D055815:Young Adult
human; plasticity; sensorimotor deprivation; transcranial magnetic stimulation