The concepts of thresholds of ischaemia in relation to brain structure and function.

The relationship between the blood supply of a neurone and its capacity to function and survive remains of fundamental importance in the study of cerebral vascular disease from both the surgical and the medical standpoint. Thus it has been assumed that a matter of only a few minutes is necessary to cause complete and permanent loss of function of key neurones in the primate nervous system (Dennis and Kabat, 1939; Weinberger et al, 1940; Grenell, 1946; Boyd and Connolly, 1962), but everyday clinical experience confirms that dense neurological deficits following soon after a cerebral ischaemic episode may gradually resolve and finally even disappear. It has long been an intriguing clinical question whether such resolution of neurological