Abstract
For patients undergoing prolonged bed rest, inactivity results in a decline in multiple physiological systems that can be attenuated by physical exercise in the hospital such as walking. In addition, non-voluntary activation of skeletal muscles can produce some benefits similar to walking. We hypothesize that rhythmical muscle stimulation of small muscles of the hand, in contrast to sensory stimulation of the skin, will lead to patterns of functional connectivity in the brain that reflect central mechanisms behind some of the physiological benefits afforded by exercise. Using a 2x2 design, healthy participants (age 21 to 31) underwent resting-state functional magnetic resonance imaging (rsfMRI) immediately before and after a45 minute treatment with either muscle stimulation (2 Hz) or skin stimulation (100 Hz) to the left hand. Six of eight participants responded to the rhythmical muscle contractions in a manner consistent with endorphin release. Functional connectivity data were analyzed using CONN toolbox software. Relative to skin stimulation, rhythmic muscle stimulation led to significant differences in connectivity with regions associated with the autonomic and limbic systems, including the hypothalamus, amygdala, periaqueductal grey, thalamus, basal ganglia, plus insulae and cingulate cortices. In addition, the rhythmic muscle stimulation led to changes in several previously identified resting state networks. In conclusion, distinct networks of the human central nervous system appear to play roles in the outcomes reported for therapeutic use of rhythmical muscle stimulation of hand muscles. These outcomes support the use and future development of similar treatment protocols for bedridden patients or people unable to engage in daily exercise.