title: Neuromodulation and rehabilitation with brain-computer interfaces and Spinal Cord Stimulation
Creators: name: McGeady, Ciarán A.
Publisher: name: University of Glasgow
Year: 2022

description: Consequences of spinal cord injury (SCI) are often severe and life-altering. Recovery of hand and arm function is consistently reported by SCI individuals as their greatest priority in terms of rehabilitation. Yet current strategies provide poor-to-modest outcomes. Innovation is required to improve traditional approaches to upper limb rehabilitation. The current view is that, due to the multi-faceted nature of SCI pathology, effective treatment will take a combinational approach. This thesis brings together two emerging and promising technologies—transcutaneous spinal cord stimulation (tSCS) and brain-computer interfaces (BCIs)—in order to judge their complimentary nature as tools for neurophysiological assessment and rehabilitation following SCI. There is growing evidence that cervical tSCS combined with intensive physical training can lead to lasting functional improvements in individuals with chronic SCI. The mechanisms underpinning tSCS-facilitated recovery, however, are still a matter of ongoing research, with conflicting reports of the impact of tSCS on cortical and spinal excitability. Evoked and reflexes have so far been the primary method of quantifying corticospinal excitability. The research undertaken in this thesis first explores electroencephalography (EEG) as a potential complementary method for assessing neuromodulation following tSCS. Due the novelty of the research, a preliminary investigation was undertaken to establish the feasibility of EEG monitoring during cervical tSCS. In a cohort of twenty-one able-bodied individuals, it was demonstrated that tSCS presented as low-latency, high-amplitude artefacts in EEG time series, at a rate equal to the stimulation frequency. Descriptive statistics were used to characterise the impact of tSCS, and judge the effectiveness of noise-attenuation techniques. Results showed that, with artefact-suppression, EEG recorded during tSCS could be returned to levels statistically similar to that of EEG acquired without tSCS interference. Additionally, it was established that neural components, such as the individual alpha frequency, were recoverable, demonstrating the feasibility of EEG as a tool for tracking cortical activity during tSCS. A subsequent study was conducted to investigate the neuromodulatory potential of tSCS on cortical activity. EEG was recorded during upper limb movements in 30 individuals both with and without concurrent cervical tSCS. Stimulation was delivered to the cervical region of the neck at intensities matching the individual’s highest tolerance without causing pain. It was found that cortical oscillatory dynamics were unaffected over a cohort of neurologically intact participants. However, a weak inhibitory effect was measured amoing individuals who received the highest stimulation intensities. A final study was devised to explore the potential of movement priming for tSCS-facilitated upper limb therapy in an individual with chronic AIS A cervical SCI. Movement priming was achieved by encouraging the participant to engage in repetitive bimanual hand movements with respect to their sensorimotor cortical activity as measured with EEG. A BCI provided real time feedback of the participant’s motor engagement in the form of a computer game, allowing them to actively engage regardless of impairment level. The participant first underwent an initial phase of 15 sessions of tSCS training alone followed by a second phase of 15 sessions of BCI priming and tSCS training. The participant’s strength and dexterity improved across both phases of the study. BCI priming may have contributed to an enhanced effect in some measures such as improved bilateral finger strength, but due to mixed results across functional measures no firm conclusions can be drawn. Nevertheless, the functional improvements lend greater credibility to cervical tSCS as a strategy for upper limb rehabilitation.