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.
['Rosenkranz|Karin|K|', 'Seibel|Julia|J|', 'Kacar|Aleksandra|A|', 'Rothwell|John|J|']
D000328:Adult D000704:Analysis of Variance D001703:Biophysics D004558:Electric Stimulation D004576:Electromyography D019054:Evoked Potentials, Motor D005260:Female D006225:Hand D006801:Humans D008297:Male D009044:Motor Cortex D009473:Neuronal Plasticity D011930:Reaction Time D012683:Sensory Deprivation D013997:Time Factors D050781:Transcranial Magnetic Stimulation D014953:Wrist D055815:Young Adult
sensorimotor deprivation plasticity human transcranial magnetic stimulation