Changes in the complex permittivity during spreading depression in rat cortex

With recent developments in current density imaging (CDI), it is feasible t o utilize this new technique in brain imaging applications. Since CDI's abi lity to measure changes in current density depends on a concomitant activit y-dependent change in the conductivity of the brain tissue, we have examine d the changes in complex conductivity during spreading depression (SD) in r odent neocortex using a coaxial probe. SD was chosen because it is often re ferred to as an animal model of cerebral ischemia and migraine with aura. T he conductivity measurements revealed a change with Short latency (30-60 s) followed by a change with a longer latency (200-300 s), This change in con ductivity with short latency has not been reported before, and we conjectur e that it may be the priming or triggering mechanism prior to the main SD e pisode. A 20% change in conductivity during SD is sufficiently large to be measured by CDI, Therefore, the ability to measure changes in the conductiv ity, as opposed to metabolic changes, makes CDI a viable approach to the st udy of ischemia and migraine with aura.