Figure 7.

Results of the transmission and posterior summation of β signals (band pass-filtered noise within 20–30 Hz) simulating the propagation of β activity through the corticospinal tract to lower motoneurons. Simulations use a population of 10⁶ axons of 800 mm of length (similar to the estimated length of corticomotoneural cells to the TA) and axon diameters (and conduction velocities) based on previously published work (Firmin et al., 2014). A, Cumulative probability function of delay estimates considering the measured axon diameters in Monkey CS28 in Firmin's article (gray line) and the axon diameter distribution obtained by fitting a lognormal function to actual data (black line). B, Histogram of the distribution of transmission delays used for the simulation (obtained using the fitted lognormal function shown on panel A). C, D, Transmission delays and normalized rms amplitudes for different scenarios simulated in which different percentages of the fastest axons transmit the (cortical) β signal. Amplitudes panel D result from summing the contributions of all axons transmitting β and dividing by the total number of axons simulated (10⁶) and by the rms amplitude of the input signal.