Sensory feedback in motor control is widely recognized to be the key link between the activity of the primary motor cortex to the motor behavior. Through an ad-hoc developed procedure for source extraction (functional source separation), the primary sensory and motor cortex activities (FS(S1), and FS(M1)) were obtained from magnetoencephalographic recordings during a sensorimotor task sequence, and sensorimotor interaction was assessed. Source activity spectral powers were evaluated in the alpha (8-13 Hz), beta (14-32 Hz), gammal (33-60 Hz) and gamma2 (61-90 Hz) frequency bands. FS(S1) and FS(M1) had different spectral properties, with FS(S1) prevailing in alpha and FS(M1) in gamma band. Both FS(S1) and FS(M1) were reactive in the different sensorimotor tasks with respect to rest in all frequency bands, except for gamma2. During an isometric contraction, we searched for an index dependent on the performance level and with low variability in the healthy population. We found these properties satisfied within a relationship between FS(S1) and FS(M1) in the gamma2 band. This sensorimotor feedback efficiency index quantitatively estimates the continuous functional balance between primary sensory and motor areas devoted to hand control and seems promising for future developments, as it is easily assessable in patients.
