No evidence of neural adaptations following chronic unilateral isometric training of the intrinsic muscles of the hand: a randomized controlled study.

PURPOSE: To test whether long-term cortical adaptations occur bilaterally following chronic unilateral training with a simple motor task. METHODS: Participants (n = 34) were randomly allocated to a training or control groups. Only the former completed a 4-week maximal-intensity isometric training of the right first dorsal interosseus muscle through key pinching. Maximal strength was assessed bilaterally in four different movements progressively less similar to the training task: key, tip and tripod pinches, and handgrip. Transcranial magnetic stimulation was used to probe, in the left and right primary hand motor cortices, a number of standard tests of cortical excitability, including thresholds, intra-cortical inhibition and facilitation, transcallosal inhibition, and sensory-motor integration. RESULTS: Training increased strength in the trained hand, but only for the tasks specifically involving the trained muscle (key +8.5 %; p < 0.0005; tip +7.2 %; p = 0.02). However, the effect size was small and below the cutoff for meaningful change. Handgrip and tripod pinch were instead unaffected. There was a similar improvement in strength in the untrained hand, i.e., a cross-education effect (key +6.4 %; p = 0.02; tip +4.7 %; p = 0.007). Despite these changes in strength, no significant variation was observed in any of the neurophysiological parameters describing cortico-spinal and intra-cortical excitability, inter-hemispheric inhibition, and cortical sensory-motor integration. CONCLUSIONS: A 4-week maximal-intensity unilateral training induced bilaterally spatial- and task-specific strength gains, which were not associated to direct or crossed cortical adaptations. The observed long-term stability of neurophysiological parameters might result from homeostatic plasticity phenomena, aimed at restoring the physiological inter-hemispheric balance of neural activity levels perturbed by the exercise. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov identifier NCT02010398.

Comparison of brainstem reflex recordings and evoked potentials with clinical and MRI data to assess brainstem dysfunction in multiple sclerosis: a short-term follow-up.

Brainstem dysfunctions are associated to high risk of developing severe disability in patients with multiple sclerosis (PwMS), often undetected by conventional routine assessments. In this view, the purpose of this study was to monitor brainstem function over a short-term period in PwMS, comparing clinical and magnetic resonance imaging (MRI) examinations with evoked potentials (EPs) and brainstem reflexes (BSRs). Forty-five PwMS were evaluated at baseline and after 15.1 ± 4.2 months through Expanded Disability Status Scale (EDSS) score, MRI, EPs, vestibulo-masseteric (VMR), acoustic-masseteric (AMR), vestibulo-collic (VCR) and trigemino-collic (TCR) reflexes. At baseline, brainstem alterations were detected by EDSS, MRI, EPs and BSRs in 40, 77.8, 84.4 and 82.2 % of patients, respectively. At follow-up, EDSS and MRI remained unchanged, while EP and BSR deteriorated in 86.7 and 91.1 % of patients, respectively. Changes from 1 to 3 altered EPs and from 1 to 4 altered BSRs were significant only for EPs (p = 0.028). The analysis of grading severity for each test disclosed significant worsening of the VMR, AMR, TCR and P14 wave of the median somatosensory EP. Combined EP/BSR recordings were significantly more sensitive than paired EDSS/MRI assessments at baseline (93.3 versus 80 %; p = 0.006) and follow-up (97.8 versus 82.2 %; p = 0.008). In the short-term VMR, AMR, TCR and P14 wave disclosed a significant functional brainstem deterioration by detecting lesions that remained clinically and MRI silent. Our findings provide evidence for a valuable role of neurophysiological methods, especially BSRs, in investigating and monitoring brainstem dysfunctions in MS, in comparison with the standard clinical and MRI procedures.