Rhythmic neural dynamics in the sensorimotor system : the role and mechanism of beta oscillations

• Main Author: Barone, Jacopo
• Format: Dissertation
• Language: English
• Published: Cardiff University 2023

Oscillatory neural activity in the beta band has been consistently observed across the sensorimotor cortex. Neurological disorders that primarily affect the motor system are often linked with alterations in beta dynamics. This has led many researchers to hypothesise a key role for this rhythm in somatosensory processing and motor control. An agreement on the supposedly beta's functional role, however, is currently lacking. This thesis studied beta oscillations while focusing on two main aspects: the role of beta in complex motor functions and the physiological mechanism behind its generation. In the first two chapters, we explored the role of beta in the sensorimotor system by employing a joystick-reaching task while recording neural activity with MEG. We first investigated the relationship of beta oscillations with learning in a motor adaptation task. After being exposed to adaptation-inducing errors, post-movement beta activity was reduced. This effect, however, was short-lived and widely spread across a set of frontoparietal nodes, suggesting a link with generalised error monitoring. We then focused on the potential "inhibitory" role of beta in a stop-signal paradigm. We contrasted activity in IFG and pre-SMA during successful and unsuccessful stopping. Although we used standard (averaged) and beta-burst (single-trial) analyses, no differences were observable between conditions. Taken together, our findings on beta's functional role produced mixed results when compared with the existing literature. In the third chapter, we shifted our focus to the physiological mechanisms behind beta origin. We investigated the relationship between GABA and beta in a pharmaco-MEG study. We additionally employed a set of novel techniques for power spectra parametrisation, which successfully separated neural activity into rhythmic and arrhythmic components. While we confirmed a modulation of beta oscillations after GABAergic interventions, we also showed a dynamic change in the aperiodic activity. These findings, however, were not observable across canonical averaged spectrograms, where periodic and aperiodic components conflated masking the true effect of GABA. We suggest that failing to dissociate between rhythmic and arrhythmic neural features could result in a misinterpretation of the underlying physiology of beta oscillations.