A vast body of research suggests that the primary motor cortex is involved in motor imagery. This raises the issue of inhibition: how is it possible for motor imagery not to lead to motor execution? The motor execution threshold may be "upregulated" during motor imagery to prevent execution. Alternatively, it has been proposed that, in parallel to excitatory mechanisms, inhibitory mechanisms may be actively suppressing motor output during motor imagery. These theories are verbal in nature, with well-known limitations. We introduced a toy-model of the inhibitory mechanisms thought to be at play during motor imagery to disentangle predictions from competing hypotheses. The toy model provides a simplified overarching description of how the motor system is involved over time during motor imagery and has been shown to predict well mental chronometry data (reaction times and imagined movement times).
The model provides a simplified overarching description of how the motor system is involved over time during motor imagery. This overall level of activation is modelled as a rescaled lognormal function defined by two parameters: the peak latency and the width of the function. The model also assumes a threshold parameter to account for the onset and duration of imagined movements. It therefore predicts -- and is fitted on -- reaction times (i.e., when imagined movements start) and movement times (i.e., how long imagined movements last).
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