Brain oscillations, connectomes and neurophysiology

Liuzzi, Lucrezia (2019) Brain oscillations, connectomes and neurophysiology. PhD thesis, University of Nottingham.

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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: Thesis (University of Nottingham only) (PhD)
Supervisors: Brookes, Matthew J.
Morris, Peter
Keywords: magnetoencephalography; MEG; functional connectivity; MRS; magnetic resonance spectroscopy
Subjects: R Medicine > RC Internal medicine > RC 321 Neuroscience. Biological psychiatry. Neuropsychiatry
Faculties/Schools: UK Campuses > Faculty of Science > School of Physics and Astronomy
Item ID: 56801
Depositing User: Liuzzi, Lucrezia
Date Deposited: 04 Sep 2019 12:12
Last Modified: 07 May 2020 08:16

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