High-gamma band activity of primary hand cortical areas: a sensorimotor feedback efficiency index

Purpose: Sensory feedback in motor control is widely recognized to be the key link between the activity of the primary motor cortex to the motor behaviour. The aim of our study was twofold: first, to characterize the functional involvement of the primary sensory (S1) and motor (M1) areas oscillatory activities in different frequency bands during a sensorimotor task sequence; second, to possibly identify an index of 'sensorimotor feedback efficiency', describing the M1-S1 functional relationship and showing a dependence on the performance level and low variability. Method: Eleven healthy volunteers (4 females, mean age 39±14 [24-66] years) were enrolled. Through an ad-hoc developed procedure for source extraction (functional source separation), the primary sensory and motor cortex activities (FSS1 and FSM1) were obtained from magnetoencephalographic recordings during a sensorimotor task sequence, i.e. an isometric opposition of the thumb to the other fingers while pressing a water sphygmomanometer under visual check, and sensorimotor interaction was assessed. Both during the rest and contraction periods, a 10-s-long train electric pulses was delivered to the median nerve at the wrist. Source activity spectral powers were evaluated in the alpha, beta, gamma1, and gamma2 frequency bands. Results: FSS1 and FSM1 had different spectral properties, with FSS1 prevailing in alpha and FSM1 in gamma band. Both FSS1 and FSM1 were reactive in the different sensorimotor tasks with respect to rest in all frequency bands, except for gamma2. During isometric contraction, we found in the gamma2 band an index with dependence on the performance and low variability describing the relationship between FSS1 and FSM1. Conclusion: We found a "sensorimotor feedback efficiency index" that 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.