The α-motoneuron pool as transmitter of rhythmicities in cortical motor drive

Abstract 

Objective

Investigate the effectiveness and frequency dependence of central drive transmission via the α-motoneuron pool to the muscle.

Methods

We describe a model for the simulation of α-motoneuron firing and the EMG signal as response to central drive input. The transfer in the frequency domain is investigated. Coherence between stochastical central input and EMG is also evaluated.

Results

The transmission of central rhythmicities to the EMG signal relates to the spectral content of the latter. Coherence between central input to the α-motoneuron pool and the EMG signal is significant whereby the coupling strength hardly depends on the frequency in a range from 1 to 100Hz. Common central input to pairs of α-motoneurons strongly increases the coherence levels. The often-used rectification of the EMG signal introduces a clear frequency dependence.

Conclusions

Oscillatory phenomena are strongly transmitted via the α-motoneuron pool. The motoneuron firing frequencies do play a role in the transmission gain, but do not influence the coherence levels. Rectification of the EMG signal enhances the transmission gain, but lowers coherence and introduces a strong frequency dependency. We think that it should be avoided.

Significance

Our findings show that rhythmicities are translated into α-motoneuron activity without strong non-linearities.

Keywords: Motoneuron pool, Corticomuscular coherence, α-Motoneuron model, Corticomuscular transmission, Motor drive, Motor unit firing