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Characterising the frequency response of impedance changes during evoked physiological activity in the rat brain

Faulkner, M; Hannan, S; Aristovich, KY; Avery, J; Holder, DS; (2018) Characterising the frequency response of impedance changes during evoked physiological activity in the rat brain. Physiological Measurement , 39 (3) , Article 034007. 10.1088/1361-6579/aab01f. Green open access

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Abstract

Electrical Impedance Tomography (EIT) can image impedance changes associated with evoked physiological activity in the cerebral cortex using an array of epicortical electrodes. An impedance change is observed as the externally applied current, normally confined to the extracellular space is admitted into the conducting intracellular space during neuronal depolarisation. The response is largest at DC and decreases at higher frequencies due to capacitative transfer of current across the membrane. Biophysical modelling has shown that this effect becomes significant above 100 Hz. Recordings at DC, however, are contaminated by physiological endogenous evoked potentials. By moving to 1.7 kHz, images of somatosensory evoked responses have been produced down to 2 mm with a resolution of 2 ms and 200 µm. Hardware limitations have so far restricted impedance measurements to frequencies < 2 kHz. The purpose of this work was to establish the optimal frequency for extending EIT to image throughout the brain and to characterise the response at frequencies > 2 kHz using improved hardware. <i>Approach</i>. Impedance changes were recorded during forepaw somatosensory stimulation in both cerebral cortex and the VPL nucleus of the thalamus in anaesthetised rats using applied currents of 1 kHz to 10 kHz. <i>Main results</i>. In the cortex, impedance changed by -0.04 ± 0.02 % at 1 kHz, reached a peak of -0.13 ± 0.05 % at 1475 Hz and decreased to -0.05 ± 0.02 % at 10 kHz. At these frequencies, changes in the thalamus were -0.26 ± 0.1 %, -0.4 ± 0.15 % and -0.08 ± 0.03 % respectively. The signal-to-noise ratio (SNR) was also highest at 1475 Hz with values of 29.5 ± 8 and 31.6 ± 10 recorded from the cortex and thalamus respectively. <i>Significance</i>. This indicates that the optimal frequency for imaging cortical and thalamic evoked activity using fast neural EIT is 1475 Hz.

Type: Article
Title: Characterising the frequency response of impedance changes during evoked physiological activity in the rat brain
Location: England
Open access status: An open access version is available from UCL Discovery
DOI: 10.1088/1361-6579/aab01f
Publisher version: https://doi.org/10.1088/1361-6579/aab01f
Language: English
Additional information: As the Version of Record of this article is going to be/has been published on a gold open access basis under a CC BY 3.0 licence (https://creativecommons.org/licenses/by/3.0/), this Accepted Manuscript is available for reuse under a CC BY 3.0 licence immediately.
Keywords: Electrical Impedance Tomography, evoked potentials, fast neural EIT
UCL classification: UCL
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
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Med Phys and Biomedical Eng
URI: https://discovery.ucl.ac.uk/id/eprint/10044045
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