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Temporal aspects of motor control
Hans-Joachim FreundNeurologische Klinik, Universität Düsseldorf, 40225 Düsseldorf, Germany
Analysing brain oscillations in relation to motor control paradigms makes it necessary to recognize some of the relevant temporal properties. The firing of motor units covers the range of partial fusion of the muscle fibers and extends from 6 to 30 Hz. The fastest possible alternating human finger or hand movements cannot exceed rates above 7 - 8 Hz. Consequently, movements are confined to the range below the firing rates. Both rates are immediately adjacent but not overlapping.
The twitch contractions of motor units start partial fusion around 6 - 8 Hz. Firing rate modulation below this would not alter force output. The same applies to the muscles so that contractions exceeding 8 Hz would not achieve fully separated movements.
A key element of motor control that must be matched by any descending command is the similarity between the innervation and the contractile properties of single motor units and muscles that operate on either side of the onset range for partial fusion. It will be interesting to see whether a pulse code can be detected for such signals in the cortical motor areas.
