In animal models of focal cerebral ischaemia, usually induced by occlusion of the middle cerebral artery, a spontaneous phenomenon occurs around the periphery of the core territory, with electrophysiological features essentially identical with CSD, and similar capacity to propagate across cerebral cortex. Designated "peri-infarct depolarisation" (PID), this event is associated with infarct expansion, or recruitment of at-risk cortical territory into the expanding core, and has been shown capable of causing this expansion, in the absence of therapeutic intervention. Indeed it has been hypothesized that glutamate release may be involved in PID generation, and that excitotoxicity may accomplish detrimental effects via this route (Hossmann, K. A. 1994), (Obrenovitch, T. P. and Urenjak, J. 1997). Some experimental neuroprotection treatments for stroke act to decrease the incidence of PID (Iijima, T. et al. 1992;Chen, Q. et al. 1993;Busch, E. et al. 1996).