Resolving functions of neurons and connections of the human corticospinal system

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An important part of the nervous system for movement control is the motor cortex and the spinal cord, which are connected via the corticospinal pathway and also via different brainstem pathways. Classically, motor cortex was considered as a relay station, forwarding information that is produced at the level of the brain to the spinal cord and to the skeletal muscles. However, accumulating evidence over recent years from studies investigating the intricate circuits of motor cortex and connections to the spinal cord suggest that these structures are crucial for a variety of features, ranging from the control of coordinated actions, to action inhibition, to decision making and to learning. The current project takes up some of the recent developments and aims to advance this knowledge with view to the human nervous system. Therefore, we will apply a non-invasive electrophysiological technique consisting of transcranial magnetic stimulation (TMS) combined with spinal H-reflexes. The method allows to probe neural activity changes at three different levels of the corticospinal system, namely: i) changes in corticospinal transmission to spinal motoneurones, ii) changes in activity of corticospinal output neurons in motor cortex, and iii) changes in activity of more complex circuits of motor cortex. The central hypothesis of the planned investigations is that these three components will have different roles in controlling dexterous movements, in motor decision making, and in motor learning, and thus will show selective activity modulations that relate to dexterity, aspects of decision making and motor learning. The expected results from our investigations aim to improve the current understanding of the function of the tested components in human movement control.