AUTHOR=Kurz Alexander , Leukel Christian TITLE=Excitability of Upper Layer Circuits Relates to Torque Output in Humans JOURNAL=Frontiers in Human Neuroscience VOLUME=13 YEAR=2019 URL=https://www.frontiersin.org/journals/human-neuroscience/articles/10.3389/fnhum.2019.00359 DOI=10.3389/fnhum.2019.00359 ISSN=1662-5161 ABSTRACT=

The relation between primary motor cortex (M1) activity and (muscular) force output has been studied extensively. Results from previous studies indicate that activity of a part of yet unidentified neurons in M1 are positively correlated with increased force levels. One considerable candidate causing this positive correlation could be circuits at supragranular layers. Here we tested this hypothesis and used the combination of H-reflexes with transcranial magnetic stimulation (TMS) to investigate laminar associations with force output in human subjects. Excitability of different M1 circuits were probed at movement onset and at peak torque while participants performed auxotonic contractions of the wrist with different torque levels. Only at peak torque we found a significant positive correlation between excitability of M1 circuits most likely involving neurons at supragranular layers and joint torque level. We argue that this finding may relate to the special role of upper layer circuits in integrating (force-related) afferent feedback and their connectivity with task-relevant pyramidal and also extrapyramidal pathways projecting to motoneurones in the spinal cord.