The cortical activation differences between proximal and distal joint movements of the upper extremities: A functional NIRS study

Motor control of musculature of proximal and distal joints has been suggested to differ. However, no study comparing patterns of activation between movements of proximal and distal joints has been conducted. In this study, using functional near infrared spectroscopy (fNIRS), we attempted to compare patterns of cortical activation generated during movements of shoulder and hand.Nine normal subjects were recruited. fNIRS was performed using a fNIRS system with 49 channels. Flexion-extension movements of the right shoulder or hand were performed. We measured values of oxy-hemoglobin (HbO) and total-hemoglobin (HbT) in three regions of interest: the primary sensory-motor cortex (SM1), the premotor cortex (PMC), and the prefrontal cortex (PFC). The relative activation ratio of HbO and HbT was estimated for comparison of the relative activity of the left PMC or PFC to the left SM1.Mean values of HbO and HbT of the left SM1, PMC, and PFC were higher during movements of the right shoulder, compared with movements of the left hand. Relative activation ratios for movements of the right shoulder (HbO: PMC-104.5%, PFC-110.9%; HbT: PMC-136.3%, PFC-200.1%) were greater than 100%, and, by contrast, less than 100% (HbO: PMC-57.5%, PFC-84.8%; HbT: PMC-88.9%, PFC-70.3%) for movements of the right hand.Our results appear to indicate that movements of the shoulder require greater neural recruitment than movements of the hand. In addition, the PMC and PFC appeared to have greater involvement than the SM1 in movements of the shoulder; by contrast, the SM1 appears to have greater involvement than the PMC and PFC in movements of the hand.