Dynamic causal modelling of MVC-normalised isometric wrist extension and wrist flexion using high-resolution EEG

Mohamed, Abdul Khaaliq
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Motor control information extracted from electroencephalography (EEG) can be used by a brain-computer interface (BCI) to control a bionic hand. This could assist individuals who have lost hand functionality. Interpreting the neural control information associated with wrist extension (WE) and wrist flexion (WF) movements is particularly challenging and currently limited. Dynamic causal modelling (DCM) was thus used in this thesis to elucidate the underlying control mechanisms of WE and WF motor tasks. The neural control of the WE and WF, and the neural mechanism of their differentiation, were hypothesised to rely on linear and non-linear, cross-frequency, causal communication between seven brain regions, using the full EEG frequency spectrum. These regions included: the hand homunculi of the primary motor cortex (M1-H), the ventral premotor cortices (PMv), the prefrontal cortices (PFC) and the supplementary motor cortex. A 128-channel EEG dataset was recorded from 14 participants while they performed repetitions of isometric WE and WF, normalised by their maximum voluntary contractions. The EEG data was fitted to 12 DCM architectures, which were compared using Bayesian model selection. The best performing model suggested that the control of the wrist motor tasks, and their differentiation, involved cross-frequency, bilateral couplings, both linear and nonlinear, involving all seven regions and the full EEG spectrum. Furthermore, DCM revealed that bilateral PMv, bilateral PFC and the high-gamma band played a significant role in the control and differentiation of the wrist motor tasks. The results suggest that future BCI and neurophysiological studies, involving WE and WF, or other hand movements, include a broad range of brain regions and frequencies in their analysis.
A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Faculty of Engineering and the Built Environment, School of Electrical and Information Engineering, University of Witwatersrand, Johannesburg, 2022