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Denyer, Ronan

University of British Columbia

The dorsal premotor cortex (PMd) and its connections with the primary motor cortex (M1) is thought to be important in the control of asymmetric rhythmic bimanual movements. However, it is uncertain if this brain-behaviour relationship arises because PMd is specifically tasked with programming of asymmetric bimanual movements, or more generally tasked with managing the increased cognitive load associated with asymmetric movements. In the current dissertation, I conducted 4 experiments to probe these questions regarding the role of PMd in bimanual control. In experiment 1, I employed dual coil transcranial magnetic stimulation (TMS) to assess whether PMd-M1 interhemispheric communication differed during preparation of unimanual and bimanual movements. I discovered that PMd-M1 interhemispheric inhibition is released during unimanual but not bimanual movement preparation, suggesting PMd-M1 interhemispheric circuits may not be actively involved in controlling descending output during bimanual behaviours. In experiment 2, I found that temporal coupling of rhythmic movements was enhanced when symmetric patterns were required compared to asymmetric patterns, and when spatially congruent timing cues were used instead of symbolic cues. These effects were restricted to high movement frequencies, and a follow up experiment 3 indicated this may have been driven by a change in movement strategy. Results from experiments 1-3 provided a platform to interrogate the central question of the dissertation. If PMd is specifically responsible for programming asymmetric movement patterns, then (1) I would expect disruption of PMd by repetitive TMS (rTMS) to result in detriments to performance of asymmetric bimanual tapping patterns only, regardless of how movement frequency is cued. If PMd is responsible for managing cognitive load, then (2) I would expect detriments to performance to scale with the degree of cognitive load engendered by task conditions. To test these competing predictions, in experiment 4 participants performed bimanual rhythmic tapping tasks used in after receiving inhibitory rTMS over right PMd. Hypotheses (1) and (2) were not supported. Instead, rTMS had no effect on behaviour. These results indicates that asymmetric bimanual control is likely enacted by a distributed cortical network beyond PMd, which is capable of compensating for neuronal challenge to right PMd to maintain behavioural output.

Text

2024-05-03

Attribution-NonCommercial-ShareAlike 4.0 International

http://hdl.handle.net/2429/88190

Neuroscience

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-sa/4.0/