Towards human motor augmentation by voluntary decoupling beta activity in the neural drive to muscle and force production.

Effective human motor augmentation should rely on biological signals that can be volitionally modulated without compromising natural motor control. We provided human subjects with real-time information on the power of two separate spectral bands of the spiking activity of motor neurons innervating the tibialis anterior muscle: the low-frequency band (<7Hz), which is directly translated into natural force control, and the beta band (13-30Hz), which is outside the dynamics of the neuromuscular system. Subjects could gain control over the powers in these two bands to navigate a cursor towards specific targets in a 2-D space (experiment 1) and to up- and down-modulate beta activity while keeping steady force contractions (experiment 2). Results indicate that beta projections to the spinal motor neuron pool can be voluntarily controlled partially decoupled from natural muscle contractions and, therefore, they could be valid control signals for implementing effective human motor augmentation platforms.