title: Detection of cortical spreading depression in the anaesthetised rat by impedance measurement with scalp electrodes: implications for non-invasive imaging of the brain with electrical impedance tomography.
abstract: The possible use of impedance measurement with scalp electrodes to detect intracranial events non-invasively was investigated by measuring the localised impedance changes during cortical spreading depression (CSD) in anaesthetised rats. Impedance was measured over ipsilateral fronto-parietal cortex by a four electrode method operating at 50 kHz with electrodes spaced 0.5 mm apart. Cortical impedance increased by 39% of the resting level during CSD. With scalp electrodes placed on abraded skin, an unexpected impedance decrease of 0.8% occurred, which correlated spatially and temporally with CSD. CSD was accompanied by a small rise in temperature; when scalp temperature was held constant by warming the scalp, no impedance change greater than baseline variability (+/- 0.1% of the resting impedance level) was observed. The non-invasive detection of CSD in migraine in humans may be possible by measuring the characteristic temperature-related impedance changes with Electrical Impedance Tomography and scalp electrodes.
authors.affiliation: Department of Physiology, University College, London, UK.
authors.forename: D S
authors.initials: DS
authors.lastname: Holder
mesh_terms: D000769:Anesthesia, Inhalation; D000818:Animals; D013181:Cortical Spreading Depression / Q000502:physiology*; D004566:Electrodes; D008297:Male; D010992:Plethysmography, Impedance / Q000295:instrumentation*; D051381:Rats; D011919:Rats, Inbred Strains; D012535:Scalp; D014054:Tomography / Q000295:instrumentation / Q000379:methods*