Brain oscillations, connectomes and neurophysiology
Publication Date
June 17, 2019
Creator
Abstract
Magnetoencephalography (MEG) is a neuroimaging technique allowing the investigation of brain function non-invasively, by detecting changes in magnetic fields outside the head induced by ensembles of neurons firing synchronously. Oscillatory electrophysiological activity measured using MEG has been shown to support long range functional communication in the brain, showing close resemblance to known fMRI functional networks. Interest in functional connectivity is growing as disruptions in the functional connectome have been implicated in both neurological and mental health conditions. However, the connection between brain oscillations, functional connectivity and neurochemistry still remains largely unexplored. In this thesis I aim to shed light on this connection.
The thesis begins with a description of the theory behind neural signals measurable with MEG (chapter 1) and the details of source localisation and functional connectivity (chapter 2). Following this, there are three experimental chapters:
in chapter 3 I test how practical aspects of experimental design affect the intra-subject repeatability of the MEG functional connectome. The use of a foam head-cast, which is known to improve co-registration accuracy, is shown to increase significantly the between session repeatability of both beamformer reconstruction and functional connectivity estimation. Moreover longer recordings offer a large improvements in repeatability of functional connectivity, with analysis suggesting this result is caused by a genuine effect of brain state.
In chapter 4 I present MEG data recorded during a sensory attention task, in which participants were asked to identify braille patterns presented to their fingers, whilst simultaneously switching attention between hands. Whilst a weight of evidence suggests that ‘low’ frequency (beta band) oscillations are representative of cortical inhibition, more recent studies have closely linked these same phenomena to functional connectivity. Results show that attentional modulation changes beta dynamics in primary sensory cortex, with attended stimuli generating lower post-stimulus responses (i.e. lower beta ‘rebound’); this effect is driven by the transient formation and dissolution of distributed networks, which form in response to unattended stimuli, and likely facilitate top down inhibitory influence on the primary sensorimotor cortex. The results are related to subject behaviour, with high pre-stimulus beta connectivity leading to poor task performance. Finally, in chapter 5, combining MEG and Magnetic Resonance Spectroscopy (MRS), I show that beta oscillations are directly related to GABAergic signalling. The results here presented offer a mechanistic interpretation of the role played by beta oscillations in mediating inhibition. This has implications for our understanding of neural oscillations and connectivity in both the healthy brain and a range of disorders.
Item Type
ethesis
Thesis Type
PhD
Supervisors
Subjects (LC)
Associated Schools / Departments
School of Physics and Astronomy
eprints ID
56801
UoN Repository URI
Except where otherwise noted, this item's license is described as
File(s)![Thumbnail Image]()
Name
Thesis_LL_final_v3.pdf
Type
Full-text
Description
Examined
Size
20.11 MB
Format
Adobe PDF
Checksum (MD5)
e91f1be7676056699c4c4057c214ce4c