Phase and frequency coordination between neuron firing as an integrative mechanism of human CNS self-organization

It was shown by surface electromyography (sEMG) from spinal cord injury and Parkinson's disease patients that FF-type motor units fire repeatedly at a rate of 10 Hz and FR-type motor units with approximately 3 action potentials per impulse train at 4 to 5 Hz. Such oscillatory firing was compared with the firing of alpha1, alpha2, and alpha3-motoneurons, innervating FF FR, and S-type muscle fibres, which fire oscillatory approximately at 10 Hz, 4 to 7 Hz and 1 Hz, as measured earlier with the single nerve-fibre action potential recording method from motoneuron axons. Repeated firings with impulse trains consisted of 1, 2-5, and 20-50 action potentials per impulse train respectively. Oscillatory firing of motoneurons has now been demonstrated in humans with two methods. In spinal cord injury patients it was observed that the FF-type motor units, firing normally at 10 Hz, fired for higher activations also at approximately 20 Hz. A motor program burst was generated by recruiting for the burst time motor units to fire oscillatory. It was further shown that FF-type motor units fired with relative phase and frequency coordination but non-synchronously. The coordination was between motor units firing of the same muscle and between muscles of the right and left arm. With the single-nerve fibre action potential recording method it was found earlier that alpha and gamma-motoneurons and muscle spindle afferents fired in relative coordination. There is indication that relative phase and frequency coordination is an integrative mechanism for the self-organization of the neuronal networks of the human central nervous system (CNS).