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Imaging of evoked neural activity in the rat brain using Electrical Impedance Tomography

Faulkner, Alice Constance Mayo; (2019) Imaging of evoked neural activity in the rat brain using Electrical Impedance Tomography. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Electrical impedance tomography (EIT) is a technique that can reconstruct conductivity changes in a volume from multiple transfer impedance measurements. Impedance changes associated with neuronal depolarisation can be measured and hence the use of EIT as a functional brain imaging technique has been proposed. The work presented has sought to extend EIT in the rat model from an exclusively cortical imaging technique to one sensitive to subcortical activity. Chapter 1 provides an introduction to the principles of EIT and an overview of previous EIT experiments. Chapters 2 and 3 have focused on optimising parameters for imaging subcortical activity when using cortical electrode arrays. In chapter 2, EIT protocol generation methods aimed at enhancing sensitivity to deep regions of interest in the brain were developed. The protocol that maximised the magnitude of current density was found to be optimal. The best frequency at which to conduct EIT measurements was determined in chapter 3 by characterising the impedance response in the thalamus and cortex during somatosensory stimulation using carrier frequencies up to 10 kHz. The largest SNR in both the cortex and thalamus was observed at 1475 Hz. The ability to image ascending neural activity with cortical electrodes was investigated in chapter 4. Despite using the optimised parameters found previously, the small amplitude signals from the thalamus precluded imaging deeper than the cortex. Subsequent simulations indicated that with this type of electrode, EIT imaging is limited to 2.6 mm below the cortical surface. In chapter 5, the feasibility of conducting EIT measurements with neural probes was assessed. By implementing neural probes along with cortical electrode arrays, thalamo-cortical circuitry occurring at the correct latency during somatosensory stimulation was imaged. The configuration of neural probe implemented limited the localisation accuracy of thalamic activity to 1.3 - 1.7 mm.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Imaging of evoked neural activity in the rat brain using Electrical Impedance Tomography
Event: University College London
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2019. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > UCL Queen Square Institute of Neurology
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > UCL Queen Square Institute of Neurology > Department of Neuromuscular Diseases
URI: https://discovery.ucl.ac.uk/id/eprint/10080394
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