CONTINUOUS-TIME ESTIMATION AS A BEHAVIORAL INDEX OF HUMAN CEREBRAL-ISCHEMIA DURING TEMPORARY OCCLUSION OF THE INTERNAL CAROTID-ARTERY

Objective-To determine whether a continuous time estimation task durin g test occlusions of either internal carotid artery would increase the ability to detect the earliest signs of cerebral ischaemia in the ant erior circulation. Methods-Four patients were involved in real time me asurement of their timing accuracy before, during, and after each test occlusion. While under each test condition, patients were instructed to press a mouse button connected to a computer and then to press it a gain no sooner than 10 seconds from the previous response but no longe r than 13 seconds later. While being given automated feedback on accur acy, patients were instructed to continually press the mouse on the ta rget schedule to maximise correct responses until told to stop. Result s-The data showed deterioration of timing accuracy during carotid occl usion (P < 0.05), which always preceded the onset of physical signs an d correlated in one patient with the presence of reduced regional cere bral blood flow. Conclusion-Decline of sustained attention under condi tions of test balloon occlusion of either internal carotid artery was an indicator of failure to maintain adequate cerebral blood flow to su stain normal neurological function. The demonstration of the behaviour al effects of early cerebral ischaemia shows the feasibility of an exp erimental model for the study of human brain function, and may now mak e it possible to quantify more precisely the time course of acute isch aemic events.