Funktionen von Neuronen und Verbindungen des menschlichen kortikospinalen Systems
Zusammenfassung der Projektergebnisse
An important part of the nervous system for movement control is the primary motor cortex (M1) and the spinal cord, which are connected via the corticospinal pathway and also via different brainstem pathways. Traditionally, M1 was viewed 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 M1 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. In the present project, we assessed relative contributions of corticospinal circuits with different origins to the control of coordinated movements that are either discrete or rhythmic, and to motor skill learning. The mentioned sites refer to infra- and supragranular layers of M1, and polysynaptic connections of the spinal cord, which were all targeted by an electrophysiological method involving transcranial magnetic stimulation (TMS) and peripheral nerve stimulation (PNS). With regard to rhythmic and discrete movements, we found activity modulations at supragranular layers in M1 and for polysynaptic corticospinal connections between the two movement types. However, we did not find such differences for neurons that descend from the M1 to the spinal cord at infragranular layers. These neural modulations between the two forms of movements could not be explained by differences in kinematic properties. Thus, rhythmic and discrete movements seem to involve different circuits of the corticospinal system. With regard to motor learning, we found a systematic increase in neural activity of neurons that descend from the M1 to the spinal cord at infragranular layers in the initial practice phase. This modulation may reflect changes in the recruitment, or reorganisation, of these corticospinal neurons due to training. These results from our investigations improved the current understanding of the functions of the tested components in human movement control. The results revealed that distinct parts of the corticospinal system are differently involved in controlling rhythmic versus discrete actions, and that these parts are differently contributing to short-term motor skill learning. This project focussed on selected features of motor control and motor learning, and future studies might want to extend to other fundamental aspects of motor control and learning, like the control of the upper versus lower limb, and neural activity changes occurring with different forms of motor learning (e.g., implicit learning with sensory prediction errors and reward prediction errors). The overall goal of this endeavour is a systematic understanding about the roles of different components of the (human) corticospinal system in movement control and motor learning.
Projektbezogene Publikationen (Auswahl)
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Evidence that distinct human primary motor cortex circuits control discrete and rhythmic movements. The Journal of Physiology, 598(6), 1235-1251.
Wiegel, Patrick; Kurz, Alexander & Leukel, Christian
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Training of a discrete motor skill in humans is accompanied by increased excitability of the fastest corticospinal connections at movement onset. The Journal of Physiology, 598(16), 3485-3500.
Wiegel, Patrick & Leukel, Christian
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Determining the types of descending waves from transcranial magnetic stimulation measured with conditioned H‐reflexes in humans. European Journal of Neuroscience, 54(3), 5038-5046.
Leukel, Christian & Kurz, Alexander
