fMRI for mapping the plastic somatotopy of primary somatosensory cortex - Development and clinical applications

Title	fMRI for mapping the plastic somatotopy of primary somatosensory cortex - Development and clinical applications
Author/s	Andreas Weibull
Department/s	Medical Radiation Physics, Malmö
Full-text	Available as PDF
Defence date	2009-12-11
Defence time	09:15
Defence place	Universitetssjukhuset MAS, Diagnistiskt Centrum, Ing 44, plan 2, rum 2005
Opponent	Peter Lundberg
Publication/Series	Lund University, Faculty of Medicine Doctoral Dissertation Series
Publishing year	2009
Volume	2009:119
Pages	160
Document type	Dissertation
Language	English
Publisher	Medical Radiation Physics
Abstract English	Functional magnetic resonance imaging (fMRI) is a widely used tool for studying brain function in vivo. The technique is based on acquiring brain images sensitive to the physiological response following neural activation, and hence, allows brain activity to be examined and documented. In this thesis, methods for fMRI mapping of the primary somatosensory cortex (S1) are optimised and subsequently applied in studies where a plastic reorganisation of S1 is hypothesised. Initially, the impact of spatial resolution and smoothing on fMRI data of detailed S1 activation was investigated using a theoretical model of fMRI performance. The impact of these parameters was also examined in healthy volunteers where different ﬁngers were mapped in S1. This was accomplished using computer controlled and reproducible tactile stimulation. It was found that both the optimal spatial resolution and preferred level of smoothing were intimately coupled to the experiment’s contrast-to-noise. These results were utilised for monitoring sensory activation of S1 in three cohorts where cortical reorganisation was anticipated: (i) In healthy volunteers where the volar part of the forearm was anaesthetised, (ii) in hand amputees and (iii) in subjects suffering from long-term exposure to vibrating tools. In all these groups, evidence of plastic changes in the sensorimotor system were found. This suggests that plastic processes could be an underlying mechanism for the symptoms experienced in patients following nerve injury and neuropathy. Finally, alternative methods for mapping functional networks of the sensorimotor cortex during rest were explored. We found that the resulting networks were comparable to activation maps during a ﬁnger-tapping task, although only partly overlapping. Such network maps could potentially add to our understanding of brain plasticity in this region of the brain. In conclusion, this work has improved the feasibility of monitoring plastic reorganisation in S1. This may contribute to the process of rehabilitation in patients suffering from sensory disorders following nerve injury and neuropathy.
Subject	Medicine and Health Sciences
Keywords	physiological noise, smoothing, spatial resolution, primary somatosensory cortex, cortical reorganisation, brain plasticity, fMRI, partial volume effects
ISBN/ISSN/Other	ISSN: 1652-8220 ISBN: 978-91-86443-08-5
Supervisor	Jonas Svensson
Supervisor	Sören Mattsson
Supervisor	Göran Lundborg
Additional info	The electronic version of the dissertaion does not include paper III-VI.
Part of	Investigation of spatial resolution, partial volume effects and smoothing in functional MRI using artificial 3D time series.
Part of	Optimizing the mapping of finger areas in primary somatosensory cortex using functional MRI.
Part of	Rapid cortical reorganisation and improved sensitivity of the hand following cutaneous anaesthesia of the forearm.

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