H-reflex conditioning with TMS: An important electrophysiological tool in motor neuroscience?!

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One of the major scientific questions today concerns the functioning of the human brain. A significant problem that slows down scientific progress is the availability of appropriate methods in humans that can provide detailed mechanistic answers similar to what is possible in animal and in in-vitro experiments. In motor neuroscience, a neurophysiological technique called H-reflex conditioning with transcranial magnetic stimulation (TMS) exists, with which the human corticospinal system can be investigated. With this method, synaptic activity and plasticity have been probed for a specific subset of corticospinal connections, namely the fastest (large diameter) monosynaptic corticospinal (pyramidal) pathways, which have been proposed to be only present in old world primates and humans. Recent advances with H-reflex conditioning suggest that not only the fastest but also slower conducting corticospinal (pyramidal) projections originating in the primary motor cortex (M1) may be probed. The present project aims to assess to which extent this is possible. Further, in the project it will be tested to which extent other projections originating in premotor areas can be tested by H-reflex conditioning. Finally, existing neurophysiological methods to study cortico-cortical and cortico-spinal projections (short-interval intracortical inhibition - SICI; intracortical facilitation - ICF; premotor-motor conditioning with TMS) will be combined with the H-reflex conditioning technique. The combination with existing methods and the possibility to study also slower pyramidal projections from M1 may lead to new neurophysiological tools with which the corticospinal system in humans can be better investigated in the future.