Different phases of motor skill learning appear to involve different physiological processes, with long-term potentiation (LTP) occurring at existing synapses in early and cortical reorganization involving synaptogenesis in later phases. Here, we test the evolution of skill learning-dependent changes in motor plasticity and excitability in six subjects trained to perform rapid thumb abductions over 5 d. Plasticity was examined using paired-associative stimulation (PAS) of the median nerve and motor cortex to induce LTP-like [PAS given with an interstimulus interval of 25 ms (PAS25)] or long-term depression (LTD)-like [PAS given with an interstimulus interval of 10 ms (PAS10)] plasticity. Excitability was tested by measuring recruitment of motor-evoked-potentials [input-output (IO) curve] and of short-latency intracortical inhibition (SICI curve), and sensorimotor organization (SMO). Task performance improved continuously over 5 d. After practice on day 1, the PAS25 effect reversed from facilitation to inhibition whereas the slope of the IO curve increased and the level of SICI decreased. These effects on IO curve and SICI were still present or even enhanced before the last practice on day 5, and were not changed by it. The effect of proprioceptive input from the trained muscle on SMO was also strengthened before practice on day 5. In contrast, PAS-induced plasticity was not influenced by motor practice on day 5, and had returned to prepractice values. The interference with PAS-induced plasticity suggests that the initial performance improvement relies on increasing the efficacy of existing synaptic connections. However, the long-lasting changes in the IO curve, SICI curve, and SMO suggest that continued practice enhances performance by changing Motor cortical organization. We hypothesize that new synaptic connections might have formed that allow LTP/LTD-susceptibility to be restored without reducing synaptic strength and performance skill.

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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.

Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is a chronic disease which can lead to many functional impairments, and like most other chronic disorders it might significantly affect quality of life (QoL). Information about QoL in patients with CIDP from developing countries is still lacking. We, therefore, sought to complete these data mosaic by investigating QoL in patients with CIDP from Serbia and surrounding countries. Our study comprised 106 patients diagnosed with CIDP. QoL was investigated using the Serbian version of the SF-36 questionnaire. The Medical Research Council 0-5 point scale, INCAT motor and sensory scores, Krupp's Fatigue Severity Scale, and Beck Depression Inventory were also used. Factors that significantly correlated with SF-36 total score in univariate analysis were included in the multiple linear regression analysis. Physical domains of the SF-36 were more affected than mental, and the overall score was 56.6 ± 25.4. Significant predictors of worse SF-36 score in our patients with CIDP were severe fatigue (β = - 0.331, p < 0.01), higher INCAT motor score (β = - 0.301, p < 0.01), depression (β = - 0.281, p < 0.01), being unemployed/retired (β = - 0.188, p < 0.05), and shorter duration of CIDP (β = + 0.133, p < 0.01). QoL was reduced in CIDP patients, especially in physical domains. Patients with presence of fatigue and depression, with more severe motor disability, unemployed/retired ones, and those with shorter duration of the disease need special attention of clinicians since they could be at higher risk to have worse QoL.

Individualized Neuromuscular Quality of Life questionnaire scores improved in our cohort of DM1 patients during a 6-year period. INQoL score did not correlate with progression of muscle weakness. This must be better understood before the selection of the instrument for use in trials to measure therapeutic benefit in DM1 patients.