A novel method for recording neuronal depolarization with recording at 125–825 Hz: implications for imaging fast neural activity in the brain with electrical impedance tomography

Abstract

Electrical impedance tomography (EIT) is a recently developed medical imaging method which has the potential to produce images of fast neuronal depolarization in the brain. Previous modelling suggested that applied current needed to be below 100 Hz but the signal-to-noise ratio (SNR) recorded with scalp electrodes during evoked responses was too low to permit imaging. A novel method in which contemporaneous evoked potentials are subtracted is presented with current applied at 225 Hz to cerebral cortex during evoked activity; although the signal is smaller than at DC by about 10×, the principal noise from the EEG is reduced by about 1000×, resulting in an improved SNR. It was validated with recording of compound action potentials in crab walking leg nerve where peak changes of -0.2% at 125 and 175 Hz tallied with biophysical modelling. In recording from rat cerebral cortex during somatosensory evoked responses, peak impedance decreases of -0.07 ± 0.006% (mean ± SE) with a SNR of >50 could be recorded at 225 Hz. This method provides a reproducible and artefact free means for recording resistance changes during neuronal activity which could form the basis for imaging fast neural activity in the brain.

Feasibility of imaging evoked activity throughout the rat brain using electrical impedance tomography

“…Previous measurements of cortical impedance changes during evoked activity in the cortex include those undertaken by Aristovich et al (2016) and Oh et al (2011); they reported maximum amplitudes of 0.007% and 0.1% respectively. In the current work the cortical impedance change had a larger mean amplitude of À0.16 AE 0.08%.…”

“…Multiple transfer impedance measurements are obtained through the use of a switch network which allows current to be sequentially injected through different electrode pairs. Fast neural EIT can detect impedance changes associated with ion channel opening during neuronal depolarisation (Klivington and Galambos, 1967;Oh et al, 2011;Velluti et al, 1968). Impedance changes arise as injected current, normally confined to the extracellular space due to the high membrane capacitance of neurons, can pass through open ion channels in the membrane and additionally travel in the intracellular space.…”

A Versatile and Reproducible Multi-Frequency Electrical Impedance Tomography System

“…Existing EIT systems include the KHU [12], fEITER [13], Dartmouth EIT System [14], Xian EIT system [15], Swisstom Pioneer Set (Swisstom AG, Switzerland) and systems previously developed in our laboratory at UCL [16,17]. Typically these systems have at least 32 electrodes with voltages recorded in parallel to increase frame rate, Table 1.…”

Real-time imaging of cerebral infarction in rabbits using electrical impedance tomography

“…EIT has the potential to provide a uniquely useful new imaging method in clinical or experimental neuroscience, 4 enabling the imaging of epileptic seizures 5 and bloodflow changes during cortical evoked activity 6 in humans, and of cortical spreading depression 7,8 and fast neuronal depolarization 9,10 in anaesthetized animals. Furthermore, its noninvasiveness and the fact that it does not involve ionizing radiation make EIT a potential method of continuous monitoring.…”