Force, angle, and velocity parameters of finger movements are reflected in corticospinal excitability

Abstract Identifying which movement parameters are reflected in the corticospinal excitability (CSE) will improve our understanding human motor control. Change in CSE measured with transcranial magnetic stimulation (TMS)-induced motor evoked potentials (MEPs) can probe the content of the signal from primary motor cortex (M1) through the corticospinal pathway and spinal motoneurons to the muscle. Here we used MEPs to investigate which movement-related parameters are reflected in CSE in 33 healthy adults. In three separate tasks, we evaluated which movement parameter(s), force, angle, and velocity, are reflected in the MEP amplitude during movement preparation and movement execution. Bayesian model comparison in a forward feature selection framework identified force and velocity measures as reflected in the MEP amplitude during movement preparation, and force, angle, and velocity measures as reflected in the MEP amplitude during movement execution. Importantly, we included measures of electromyography (EMG) in the forward feature selection, and the parameter measures are included only if they add explanatory power of MEP amplitude in addition to the EMG. These findings show that when taking EMG measures into account, all three movement parameters force, angle, and velocity are reflected in CSE. These findings propose a flexible and task-dependent form of signaling in the motor system that allows parameter-specific modulation of CSE to accurately control finger movements. Key pointsPrior research show that the primary motor cortex activity reflects movement parameters.Measures of the response to a magnetic stimulation, the motor evoked potential (MEP), can be used to assess the content of the signal sent to the muscle.We use Bayesian model comparison to test whether movement parameters are reflected in the models best describing the MEP amplitude modulations.We show that the MEP amplitude reflects all tested movement parameters, force, angle, and velocity.Our results indicate a task-dependent form of signaling not only in M1, but also in the corticospinal pathway and spinal motor neurons propagating the signal to the muscle.