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Objectives-In major cerebral arterial occlusive diseases, patients with inadequate blood supply relative to metabolic demand (misery perfusion) may be at increased risk for cerebral ischaemia. This study investigated whether patients showing misery perfusion on PET have a high risk of recurrent ischaemic stroke. Methods-The relation between the regional haemodynamic status of cerebral circulation and the subsequent risk of recurrent stroke was prospectively evaluated in 40 patients with symptomatic internal carotid or middle cerebral arterial occlusive diseases who underwent PET. Patients were divided into two haemodynamic categories according to the mean hemispheric value of oxygen extraction fraction in the hemisphere supplied by the artery with symptomatic disease: patients with normal oxygen extraction fraction and those with increased oxygen extraction fraction (misery perfusion). All patients were followed up for at least 12 months. Results-The one year incidence of ipsilateral ischaemic strokes for patients with normal oxygen extraction fraction and those with increased oxygen extraction fraction were two of 33 and four of seven patients respectively. A significantly higher incidence of ipsilateral strokes was found in patients with increased oxygen extraction fraction (Fisher's exact test; P = 0-005). In patients with increased oxygen extraction fraction, three of four strokes were watershed infarctions and the location of the infarction corresponded with the area of increased oxygen extraction fraction. Conclusion-These findings contradict conclusions of a previous study and suggest that patients with major cerebral arterial occlusive diseases and misery perfusion have a high risk for recurrent ischaemic stroke.(C Neurol Neurosurg Psychiatry 1996;61:18-25) Keywords: cerebrovascular disease; computed tomography; haemodynamics; stroke riskIn patients with major cerebral arterial occlusive disease, an inadequate blood supply relative to metabolic demand (misery perfusion)' may increase the risk of cerebral ischaemia, suggesting that identification and optimal treatment of patients with misery perfusion could help prevent stroke. However, it remains unclear whether patients with misery perfusion on PET have a high risk of ischaemic stroke, especially strokes of haemodynamic origin. Although case reports and retrospective studies have indicated that bypass surgery relieved patients with misery perfusion from abnormal haemodynamic state and recurring transient ischaemic attacks,'3' few studies have systematically investigated the relation between cerebral haemodynamics determined by PET and the subsequent risk of stroke. A previous longitudinal study did not find a relation between abnormal cerebral haemodynamics and the subsequent occurrence of stroke,5 but the data of the study were limited and not conclusive because of the few patients studied.2 To further investigate whether patients with misery perfusion have a high risk of recurrent ischaemic stroke, we prospectively followed up 40 medically tre...

Neuropsychological tests that require shifting an attentional set, such as the Wisconsin Card Sorting Test, are sensitive to frontal lobe damage. Although little information is available for humans, an animal experiment suggested that different regions of the prefrontal cortex may contribute to set shifting behavior at different levels of processing. Behavioral studies also suggest that set shifting trials are more time consuming than non-set shifting trials (i.e. switch cost) and that this may be underpinned by differences at the neural level. We determined whether there were differential neural responses associated with two different levels of shifting behavior, that of reversal of stimulus-response associations within a perceptual dimension or that of shifting an attentional set between different perceptual dimensions. Neural activity in the antero-dorsal prefrontal cortex increased only in attentional set shifting, in which switch costs were significant. Activity in the postero-ventral prefrontal cortex increased not only in set shifting but also in reversing stimulus-response associations, in which switch costs were absent. We conclude that these distinct regions in the human prefrontal cortex provide different levels of attention control in response selection. Thus, the antero-dorsal prefrontal cortex may be critical for higher order control of attention, i.e. attentional set shifting, whereas the postero-ventral area may be related to a lower level of shift, i.e. reorganizing stimulus-response associations.

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The Wisconsin Card Sorting Test (WCST) is used clinically for evaluating frontal lobe function, but there is some controversy as to its specificity for detecting frontal lobe damage. To investigate the cerebral regions essential to the performance of the Card Sorting Test, we measured the regional cerebral blood flow (rCBF) in 18 normal subjects by PET under the three conditions: (i) during the Modified Card Sorting Test (MCST); (ii) during a matching-to-sample (MTS) task, based on the MCST, but with selective attention to one of three stimulus categories (colour, number or shape) as a control to cancel the effects of maintenance of sets in the MCST; (iii) under resting conditions as overall control. When rCBF during the MCST was compared with that during each MTS task separately, significant activations were observed during the MCST in the left or bilateral dorsolateral prefrontal cortex (DLPFC), bilateral inferior parietal lobes, left superior occipital gyrus and left cerebellum. Compared with all the MTS tasks inclusively, significant increase in rCBF was detected during the MCST in the bilateral DLPFC, inferior parietal lobes, striate cortex, cerebellum and left occipital cortex. These results suggest the involvement of the DLPFC and other related areas such as the inferior parietal cortex in the execution of the MCST, and may help explain why a variety of brain lesions can result in impaired performance on the Card Sorting Test.