Long-lasting changes in muscle activation and step cycle variables induced by repetitive sensory stimulation to discrete areas of the foot sole during walking

We examined whether repetitive electrical stimulation to discrete foot sole regions that is phase-locked to the step cycle modulates activity patterns of ankle muscles and induces neuronal adaptation during human walking. Non-noxious repetitive foot sole stimulation (STIM; 67 pulses @333 Hz) was given to the medial forefoot (f-M) or heel (HL) regions at (1) the stance-to-swing transition, (2) swing-to-stance transition, or (3) mid-stance, during every step cycle for 10 min. Stance, but not swing, durations were prolonged f-M STIM delivered at stance-to-swing transition, and these changes remained for up to 20-30 min after the intervention. Electromyographic (EMG) burst durations and amplitudes in the ankle extensors were also prolonged and persisted for 20 min after the intervention. Interestingly, STIM to HL was ineffective at inducing modulation, suggesting stimulation location-specific adaptation. In contrast, STIM to HL (but not f-M), at the swing-to-stance phase transition, shortened the step cycle by premature termination of swing. Furthermore, the onset of EMG bursts in the ankle extensors appeared earlier than in the control condition. STIM delivered during the mid-stance phase was ineffective at modulating the step cycle, highlighting phase-dependent adaptation. These effects were absent when STIM was applied while mimicking static postures for each walking phase during standing. Our findings suggest that the combination of walking-related neuronal activity with repetitive sensory inputs from the foot can generate short-term adaptation that is phase-dependent and localized to the site of STIM.

To stimulate or not to stimulate? A rapid systematic review of repetitive sensory stimulation for the upper-limb following stroke

Background Repetitive sensory stimulation (RSS) is a therapeutic approach which involves repeated electrical stimulation of the skin’s surface to improve function. This rapid systematic review aimed to describe the current evidence for repetitive sensory stimulation (RSS) in rehabilitation of the upper-limb for people who have had a stroke. Main text Methods: Relevant studies were identified in a systematic search of electronic databases and hand-searching in February 2020. The findings of included studies were synthesized to describe: the safety of RSS, in whom and when after stroke it has been used, the doses used and its effectiveness. Results Eight studies were included. No serious adverse events were reported. The majority of studies used RSS in participants with mild or moderate impairments and in the chronic stage after stroke. Four studies used RSS in a single treatment session, reporting significant improvements in strength and hand function. Findings from longitudinal studies showed few significant differences between control and experimental groups. Meta-analysis was not possible due to the heterogeneity of included studies. Conclusions This review suggests that there is insufficient evidence to support the use of RSS for the upper-limb after stroke in clinical practice. However, this review highlights several clear research priorities including establishing the mechanism and in whom RSS may work, its safety and optimal treatment parameters to improve function of the upper-limb after stroke.

Evoking plasticity through sensory stimulation: Implications for learning and rehabilitation

The gold standard for improving sensory, motor and or cognitive abilities is longterm training and practicing. Recent work, however, suggests that intensive training may not be necessary. Improved performance can be effectively acquired by a complementary approach in which the learning occurs in response to mere exposure to repetitive sensory stimulation. Such training-independent sensory learning (TISL), which has been intensively studied in the somatosensory system, induces in humans lasting changes in perception and neural processing, without any explicit task training. It has been suggested that the effectiveness of this form of learning stems from the fact that the stimulation protocols used are optimized to alter synaptic transmission and efficacy. TISL provides novel ways to investigate in humans the relation between learning processes and underlying cellular and molecular mechanisms, and to explore alternative strategies for intervention and therapy.