70 research outputs found
Volume 36, Number 3, September 2016 OLAC Newsletter
Digitized September 2016 issue of the OLAC Newsletter
Volume 35, Number 4, December 2015 OLAC Newsletter
Digitized December 2015 issue of the OLAC Newsletter
Volume 36, Number 2, June 2016 OLAC Newsletter
Digitized June 2016 issue of the OLAC Newsletter
Volume 37, Number 2, June 2017 OLAC Newsletter
Digitized June 2017 issue of the OLAC Newsletter
Volume 39, Number 2, June 2019 OLAC Newsletter
Digitized June 2019 issue of the OLAC Newsletter
Volume 37, Number 1, March 2017 OLAC Newsletter
Digitized March 2017 issue of the OLAC Newsletter
Volume 35, Number 3, September 2015 OLAC Newsletter
Digitized September 2015 issue of the OLAC Newsletter
Volume 36, Number 1, March 2016 OLAC Newsletter
Digitized March 2016 issue of the OLAC Newsletter
Volume 36, Number 4, December 2016 OLAC Newsletter
Digitized December 2016 issue of the OLAC Newsletter
Characterising the frequency response of impedance changes during evoked physiological activity in the rat brain
OBJECTIVE: 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 using improved hardware. APPROACH: 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. MAIN RESULTS: 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 was also highest at 1475 Hz with values of -29.5 ± 8 and -31.6 ±10 recorded from the cortex and thalamus respectively. Signficance: This indicates that the optimal frequency for imaging cortical and thalamic evoked activity using fast neural EIT is 1475 Hz
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