Functional neuroimaging of the somatosensory system with Ultra-high-field fMRI and MEG

Wang, Fan (2012) Functional neuroimaging of the somatosensory system with Ultra-high-field fMRI and MEG. PhD thesis, University of Nottingham.

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Multimodal neuroimaging using a combination of Magnetoencephalography (MEG) and ultra-high-field fMRI are used in order to gain further insight into the neural oscillations and haemodynamic responses in the somatosensory cortex.

Single pulse electrical median nerve stimulation (MNS) with regular and jittered intervals is used in MEG. A preliminary study is used to determine acceptable trial number and length, and highlights points to be considered in paradigm optimization. Time-frequency analysis shows that the largest activities are beta event-related desynchronization (ERD) and event-related synchronization (ERS) between 13Hz and 30Hz. No significant difference in both the induced oscillations and evoked responses are found. Paired pulse MNS with varying ISIs are studied using MEG and 7T fMRI. The beta ERD is suggested to have a gating role with a magnitude irrespective of the starting point of stimulus. Non-linearity effects both in beta ERD/ERS and P35m are shown for ISIs of up to 2s, implying that the non-linear neural responses to the stimulus may still contribute to the BOLD non-linearity even when the evoked response has returned to baseline. Multiple pulse MNS with varying pulse train length and frequency are also investigated using MEG and MEG-fMRI. The gating role of beta ERD is further confirmed and the N160m is suggested to be modulated under this role. No accumulative effect is seen in the ERS with increasing pulse number but the amplitude of the ERS is modulated by the frequency. This can be explained by a Cortical Activation Model (CAM).

Efforts to spatially separate the beta ERD and ERS are shown for all three studies. Group averaged SAM images suggest a separation of activation areas along the central gyrus. Significant difference are found in the z MNI coordinate between beta ERD and ERS peak locations, suggesting that these two effects could arise from different generators. In the multiple pulse frequency study, by including the temporal signature of beta ERD and ERS as a regressor in BOLD fMRI analysis, delayed BOLD responses are located posterior to the standard BOLD response. However, the exact nature of the relationship between this delayed BOLD response and the ERS effects requires further work.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Morris, P.G.
Gowland, P.A.
Keywords: MEG, fMRI, Somatosensory System, Beta oscillatory activity
Subjects: R Medicine > RC Internal medicine > RC 321 Neuroscience. Biological psychiatry. Neuropsychiatry
Q Science > QC Physics
Faculties/Schools: UK Campuses > Faculty of Science > School of Physics and Astronomy
Item ID: 12402
Depositing User: EP, Services
Date Deposited: 14 Sep 2012 09:49
Last Modified: 23 Dec 2017 13:05

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