SUMMARY The oxygen-15 continuous inhalation technique and PET were used to study the age-related changes in regional CBF and CMRO 2 . Twenty-seven patients, aged 19 to 76 years, free of any history of cerebral disease and vascular risk factors were examined in "resting state." CBF, CMRO 2 and oxygen extraction fraction (OEF) values were calculated in seven different brain structures as well as in mean gray matter. Left-right ratios were also computed for all symmetrical structures analyzed.Mean gray CBF, but not mean gray CMRO 2 , decreased linearly with age (p < 0.02). However, when younger subjects (S50 yrs) were compared to older subjects (>50 yrs), an age-related matched decrease in CBF and CMRO 2 was observed in mean gray matter (18% and 17%, p < 0.05) and in all gray matter regions analyzed, particularly in frontal, temporo-sylvian and parieto-occipital cortex. White matter CBF and CMRO 2 remained remarkably stable with advancing age.Although the possibility'of methodological artifacts was considered, we favor progressive loss of cortical neurones and/or diminished activity of those remaining to explain our findings. In addition, age-related changes in cognitive activities might also be involved. Stroke Vol 15, No 4, 1984 DESPITE NUMEROUS STUDIES, 114 the effects of aging on cerebral circulation and metabolism still remain largely unsettled. Studies on global hemispheric cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO 2 ) have so far provided discrepant results: some^ concluded that CBF and CMRO 2 did not decrease with advancing age except when vascular risk factors were present, while other authors 1 2 found a parallel decline in both CBF and CMRO 2 . These discrepancies may be partially explained by different criteria for normality used. In his review on this subject, Kety 7 favored the idea that there was a rapid fall of both CBF and CMRO 2 around puberty which continued to the third decade and was followed by a more gradual decline in middle and old age.

To investigate further the topographical, clinical and temporal correlates of crossed cerebellar diaschisis (CCD) after supratentorial stroke, 55 patients suffering from a single unilateral ischaemic stroke in the carotid artery territory were studied with the quantitative oxygen-15 steady-state technique and positron tomography. Fourteen patients had one or more follow-up studies, contributing a total of 72 studies. The phenomenon of CCD, defined by depressed oxygen consumption in the contralateral cerebellum, was statistically significant in 58% of the studies. It was more prominent when the supratentorial infarct involved the internal capsule or the cortical mantle extensively, consistent with the hypothesis that it results from destruction of the corticopontocerebellar fibres. Although CCD was associated with the presence of hemiparesis, it also occurred in patients without hemiparesis and was not seen in all those with hemiparesis, suggesting that destruction of the pyramidal tract is neither necessary nor sufficient to induce CCD. Finally, CCD tended to persist over long periods of time after a stroke, pointing towards a transneuronal degeneration possibly akin to crossed cerebellar atrophy as a likely explanation for CCD. Nevertheless, CCD could be seen within hours of a stroke and sometimes disappeared within a few days, suggesting a temporal continuum between early, potentially reversible functional hypometabolism (diaschisis) and irreversible degeneration.

During the first year of life, exchanges and communication between a mother and her infant are exclusively preverbal and are based on the mother's ability to understand her infant's needs and feelings (i.e., empathy) and on imitation of the infant's facial expressions; this promotes a social dialog that influences the development of the infant self. Sixteen mothers underwent functional magnetic resonance imaging while observing and imitating faces of their own child and those of someone else's child. We found that the mirror neuron system, the insula and amygdala were more active during emotional expressions, that this circuit is engaged to a greater extent when interacting with one's own child, and that it is correlated with maternal reflective function (a measure of empathy). We also found, by comparing single emotions with each other, that joy expressions evoked a response mainly in right limbic and paralimbic areas; by contrast, ambiguous expressions elicited a response in left high order cognitive and motor areas, which might reflect cognitive effort.

In order to evaluate whether cortical motor reorganization occurs in the earliest phase of multiple sclerosis, we studied patients after a first clinical attack of hemiparesis. From a consecutive series of 70 patients enrolled in a study of patients with clinically isolated syndrome and serial MRI findings indicative of multiple sclerosis, we retrospectively selected 10 patients with hemiparesis as the onset symptom and no further clinical episode [mean age 32 +/- 9 years, disease duration 24 +/- 14 months, median Expanded Disability Status Score (EDSS) 1.25]. Ten age-matched, healthy subjects served as controls. Each subject was submitted to two functional MRI trials (one per hand) using a 1.5 T magnet during a sequential finger-to-thumb opposition task. Image analysis was performed using SPM99 software. Movements of both the 'affected' and the 'unaffected' hand activated significantly larger areas in patients than in controls in both the contralateral and ipsilateral cortical motor areas. Patients activated a greater number of foci than controls during both the right-hand and the left-hand movement. Most of these foci were located in cortical areas which were less or not at all activated in controls, such as the lateral premotor cortex [Brodmann area (BA) 6], the insula and the inferior parietal lobule (BA 40). Between-group analysis of patients versus controls showed significant (P < 0.001) foci in these areas, principally located in the ipsilateral hemisphere during right-hand movement and in both the cerebral hemispheres during left-hand movement. Time since clinical onset showed a significant positive correlation with the extent of activation in the ipsilateral motor areas (P = 0.006) during the right-hand movement and with the extent of activation in both the ipsilateral (P = 0.02) and contralateral (P = 0.006) motor areas during the left-hand movement. The T(1) lesion load along the motor pathway showed a significant positive correlation (P = 0.007) with the extent of activation in the contralateral motor areas during right-hand movement. Our study shows functional adaptive changes that involve both the symptomatic and asymptomatic hemisphere during a simple motor task in patients who had suffered a single clinical attack of hemiparesis. The extent of these changes increased with the time elapsed since disease onset and the severity of brain damage.

Positron emission tomography was used to study the effects of unilateral vascular thalamic lesions on cortical oxygen and glucose utilization in 10 patients. There was significant ipsilateral cortex hypometabolism in 9 of the 10 patients, affecting the whole cortical mantle diffusely. The only patient spared was free of neuropsychological deficit at the time of positron emission tomography. In 4 patients, the magnitude of ipsilateral cortical hypometabolism was significantly less at a follow-up PET study, when neuropsychological function had improved. When taken together, the 14 studies showed a significant tendency for the hypometabolism to improve with time after clinical onset. These data suggest that the ipsilateral cortical hypometabolism results from damage to the thalamocortical connections and reflect either loss of nonspecific activating afferences or a degenerative deafferentation-deafferentation process, or both. Its links with the concept of diaschisis are suggested by its tendency to recover. A causal relationship between cortical hypometabolism and neuropsychological deficit, however, although strongly suggested, cannot be firmly established from the present data.