Stroke risk and age do not predict behavioral activation of brain blood flow

Cognitive reserve modulates functional brain responses during memory tasks: a PET study in healthy young and elderly subjects

Cognitive reserve (CR) is the ability of an individual to cope with advancing brain pathology so that he remains free of symptomatology. Epidemiological evidence and in vivo neurometabolic data suggest that CR may be mediated through education or IQ. The goal of this study was to investigate CR-mediated differential brain activation in 17 healthy young adults and 19 healthy elders. Using nonquantitative H(2)(15)O PET scanning, we assessed relative regional cerebral blood flow while subjects performed a serial recognition memory task under two conditions: nonmemory control (NMC), in which one shape was presented in each study trial; and titrated demand (TD), in which study list length was adjusted so that each subject recognized shapes at approximately 75% accuracy. A factor score that summarized years of education and scores on two IQ indices was used as an index of CR. Voxel-wise, multiple regression analyses were performed with TD minus NMC difference PET counts as the dependent variable and the CR variable as the independent variable of interest. We identified brain regions where regression slopes were different from zero in each separate group, and also those where regression slopes differed between the two age groups. The slopes were significantly more positive in the young in the right inferior temporal gyrus, right postcentral gyrus, and cingulate, while the elderly had a significantly more positive slope in left cuneus. Brain regions where systematic relationships between CR and brain activation differ as a function of aging are loci where compensation for aging has occurred. They may mediate differential ability to cope with brain changes in aging.

Aging has a complex effect on a rat model of ischemic stroke

Stroke in humans is usually associated with advanced age. Nevertheless, almost all animal models of ischemic stroke are based on young animals. The present study was designed to assess the effect of age on the development of ischemic injury in a model of focal brain ischemia in rats. Two age groups of Wistar rats were used: young adult (3 months) and old (24-26 months). Under halothane anesthesia, polyethylene microspheres (50 microm in diameter) were injected into the left common carotid artery following a temporary occlusion of the external carotid artery. Sham-operated rats underwent the same procedure but were injected with an identical volume (100 microl) of saline only. Rats of both experimental groups displayed neurological impairment after surgery. However, contrary to expectation, the young rats were more affected than the old rats. Young rats displayed an abrupt 30% decrement in neurological functions in the first week and then showed a partial functional recovery into a 12% decrement from the second week on. Old rats developed the neurological impairment gradually over a 2-week period (6.3% in the first week and 11% in the second week and thereafter). One month later, rats were tested in a water maze task. Again, performance was more impaired in the young ischemic rats than in the old rats. Histological evaluation revealed more extensive neurological damage in young ischemic as compared to old rats. Thus, although increased age has a critical effect on the evolution of the neurological impairment following focal brain ischemia and stroke, its effects in the rat model were more pronounced in the young animals.

Age and carotid artery occlusive disease are important determinants of cerebral blood flow changes after antihypertensive therapy

STUDY OBJECTIVE

To determine the short-term effects of antihypertensive therapy on cerebral blood flow (CBF).

DESIGN

Prospective, observational study.

SETTING

A university-affiliated teaching hospital.

PATIENTS

Twenty-four patients (age range 53-85 yrs) with chronic hypertension, nine of whom had carotid artery occlusive disease (CAOD).

INTERVENTIONS

The CBF (xenon-133 inhalation technique) and blood pressure were measured before and at 60 minutes after administration of antihypertensive therapy.

MEASUREMENTS AND MAIN RESULTS

Age was inversely related to the change in CBF in patients with CAOD (p < 0.01). In all patients, the change in CBF after taking antihypertensive drugs was significantly inversely associated with baseline CBF (p < 0.01). Changes in regional CBF, measured by asymmetry scores, were significantly greater in patients with CAOD than in those without CAOD (p < 0.05).

CONCLUSIONS

Elderly patients with occlusive extracranial cerebrovascular disease are at risk of drug-induced changes in both mean and regional CBF, and may benefit from a CBF assessment before being prescribed antihypertensive therapy.

Data analysis in behavioral cerebral blood flow activation studies using xenon-133 clearance

BACKGROUND AND PURPOSE

Three mainstream strategies exist to detect the responses of regional cerebral blood flow to functional activation. We tested the significance of changes in raw regional cerebral blood flow data, regional cerebral blood flow data normalized by division by global cerebral blood flow (dependent model of the regional-to-global cerebral blood flow relation), and regional cerebral blood flow data treating global cerebral blood flow as a covariate (independent model). Both latter models attempt to enhance regional sensitivity by removing global effects. We examined the sensitivity and pitfalls of these three strategies in behavioral activation studies.

METHODS

These three strategies of data analysis were applied to changes in regional cerebral blood flow induced by a visuospatial problem-solving task in 38 healthy subjects as measured by the intravenous xenon-133 method with 32 stationary detectors.

RESULTS

Mental activation increased blood flow in all regions of interest. Raw data were most sensitive and reliable to detect responses to mental stimulation. Both the independent and dependent models to remove global effects were less sensitive and falsely indicated deactivation in regions that were clearly stimulated.

CONCLUSIONS

In behavioral activation paradigms, safe data analysis should be restricted to using raw regional cerebral blood flow increases without normalization or separation of global from regional effects. Studies using complex stimulation tasks should be scrutinized for global cerebral blood flow effects confounding regional responses.

Cerebral circulation and oxygen metabolism associated with subclinical periventricular hyperintensity as shown by magnetic resonance imaging

A combined magnetic resonance imaging and positron emission tomography study was performed on 21 patients with cerebrovascular risk factors but without neurological abnormalities. Our purpose was to investigate the hypothesis that periventricular hyperintensity (PVH) reflects ischemia. Periventricular hyperintensity was evaluated with a method we devised, and cerebral circulation and oxygen metabolism were evaluated with the oxygen-15 steady-state technique. We concluded that the brain with severe periventricular hyperintensity had abnormal circulation, although oxygen metabolism was not measurably affected. The role of a compensation mechanism under conditions of decreased oxygen supply was considered.