Sensory enhancement amplifies interlimb cutaneous reflexes in wrist extensor muscles

Abstract

Interlimb neural connections support motor tasks such as locomotion and cross-education strength training. Somatosensory pathways that can be assessed with cutaneous reflex paradigms assist in subserving these connections. Many studies show that stimulation of cutaneous nerves elicits reflexes in muscles widespread across the body and induces neural plasticity after training. Sensory enhancement, such as long-duration trains of transcutaneous stimulation, facilitates performance during rehabilitation training or fatiguing motor tasks. Performance improvements due to sensory stimulation may be caused by altered spinal and corticospinal excitability. However, how enhanced sensory input regulates the excitability of interlimb cutaneous reflex pathways has not been studied. Our purpose was to investigate the effects of sensory enhancement on interlimb cutaneous reflexes in wrist extensor muscles. Stimulation to provide sensory enhancement (2-s trains at 150 Hz to median or superficial radial nerves) or evoke cutaneous reflexes (15-ms trains at 300 Hz to superficial radial nerve) was applied in different arms while participants (n = 13) performed graded isometric wrist extension. Wrist extensor electromyography and cutaneous reflexes were measured bilaterally. We found amplified inhibitory reflexes in the arm receiving superficial radial and median nerve sensory enhancement with net reflex amplitudes decreased by 709.5% and 695.3% repetitively. This suggests sensory input alters neuronal excitabilities in the interlimb cutaneous pathways. These findings have potential application in facilitating motor function recovery through alterations in spinal cord excitability enhancing sensory input during targeted rehabilitation and sports training.