Human brain glucose utilization and cognitive function in relation to age

The effect of focal cerebral atrophy in positron emission tomographic studies of aging and dementia

We used x-ray computed tomographic (XCT) scans to measure the degree of cerebral atrophy in brain regions defined by a region of interest (ROI) anatomy atlas. The same atlas was employed for quantitation of local cerebral glucose metabolic rates (LCMRglc) by PET. PET data were obtained from 9 young controls, 7 healthy elderly controls, and 10 patients with dementia. Cerebrospinal fluid (CSF) in atrophic brain regions was assumed to be metabolically inert, and LCMRglc measurements were corrected for the degree of atrophy. Significantly greater atrophy was seen for 7 of 8 regions in comparisons between demented patients and age-matched controls. This atrophy was most pronounced in superior parietal (SP) regions. Decreases in parietal LCMRglc in dementia patients and SP LCMRglc in old controls were no longer significant after correction for atrophy. These results emphasize the need to consider focal atrophy effects in regional quantitative analyses of emission tomographic data.

Frontal hypermetabolism and thalamic hypometabolism in a patient with abnormal orienting and retrosplenial amnesia

A patient with verbal amnesia and a propensity to direct his attention to the right following a retrosplenial area lesion was studied with positron emission tomography using [F-18] fluorodeoxyglucose. These studies showed that the left thalamus was hypometabolic, and the anterior 2/3 of the left hemisphere was hypermetabolic when compared with the right. There were no significant differences seen in the medial temporal lobes. Based on this study, it is posited that interruption of hippocampal input into the anterior thalamus was responsible for the amnesia, and the left frontal hyperactivity was associated with the propensity to attend contralaterally.

Decreased glucose utilization in the striatum and frontal lobe in probable striatonigral degeneration

Nine positron emission tomography studies of regional cerebral glucose metabolism were performed in 7 patients with probable striatonigral degeneration, a disorder characterized by parkinsonian features and absent or poor response to L-dopa. When compared with values obtained in normal volunteers, mean cerebral glucose metabolism was slightly reduced in subjects with striatonigral degeneration who, in addition, had a marked (20.5%, +/- 3 SD) relative hypometabolism in putaminal and caudate nuclei. Significant hypometabolism was also found in motor/premotor as well as in prefrontal cortex. In 2 subjects who were studied twice a deterioration of relative striatal metabolism paralleled clinical evolution. Magnetic resonance imaging disclosed the presence of abnormal iron deposits in the putamen in all cases but showed no cortical anomalies. These results suggest that positron emission tomography with [18F]fluorodeoxyglucose may provide an index of cell and processes degeneration in the striatum in striatonigral degeneration and is able to detect functional deficits in frontal cortex. The presence of striatal hypometabolism might be a predictor of a poor response to L-dopa.

Traumatic brain injury, aging and reaction time

The effects of traumatic brain injury (TBI) and aging were compared on tests of simple and complex reaction time (RT). Simple RT was not significantly affected by aging or TBI. TBI patients, however, tended to be slower on Simple RT tasks, and had a larger standard deviation. Individuals over age 60 and patients of any age with TBI demonstrated slower RT with choice RT tests. In addition, both groups (those over 60 and TBI patients) were less able than other groups to inhibit the processing of redundant information. For the TBI patients, this occurred primarily on reassessment. These results suggest that the deficit in both aging and TBI is not only a generalized neuronal slowing but a more specific impairment in attentional control processes, exhibited as a deficit in focused attention.

Regional brain function in hallucinations: a study of regional cerebral blood flow with 99m-Tc-HMPAO-SPECT in patients with auditory hallucinations, tactile hallucinations, and normal controls

From the supposition that there exists a possible connection between certain psychopathological symptoms, and/or syndromes (e.g., hallucinations) and regional cerebral dysfunction, patients suffering from auditory and tactile hallucinations were investigated, in a symptom-oriented study, using the method of technetium-99m-Hexamethyl-propylenamine Oxime (99m-Tc-HMPAO)-Single Photon Emission Computed Tomography (SPECT) and compared with normal controls. The results support Jackson's hypothesis to the effect that hallucinatory phenomena will primarily occur when the normally inhibitive influence of the upper cortical centers over the lower brain structures diminishes, resulting in relative hyperactivity in the basal regions. In addition to the brain activity-changes generally observed in hallucinating patients, it was possible to identify regional cerebral blood flow (rCBF)-distribution patterns characteristic in certain forms of hallucinatory phenomena, i.e., a significant increase of activity in the hippocampal regions (including hippocampus, parahippocampus, and amygdala) only in patients with auditory hallucinations, and a significant reduction of rCBF in the inferior temporal regions in patients with tactile hallucinations.

A relationship between metabolism in frontal lobes and cerebellum in normal subjects studied with PET

Lesions of one cerebral hemisphere are associated with decreased glucose metabolism, oxygen metabolism, and blood flow in the contralateral cerebellar hemisphere. We used positron emission tomography to look for a functional relationship in cerebral metabolism between the cerebral cortex and the contralateral cerebellum in normal human subjects. Twenty-four normal subjects were scanned with [18F]fluoro-2-deoxy-D-glucose while in a resting state. Asymmetry in local CMRglu (LCMRglu) in the frontal cortex was strongly correlated with asymmetry in LCMRglu in the opposite direction in the cerebellar hemispheres (r = -0.60, p less than 0.001). Widespread subregions of the frontal cortex were found to contribute to this relationship. Considering these results together with previous studies demonstrating that frontal lesions are associated with decreased metabolism in the contralateral cerebellum, we conclude that the frontal cortex exerts a strong modulating influence on metabolism in the contralateral cerebellum in normal subjects, and that this influence may be asymmetrical.

Sensitivity of cerebral glucose metabolism to age, gender, brain volume, brain atrophy, and cerebrovascular risk factors

In 76 normal volunteers studied by positron emission tomography, with [18F]fluorodeoxyglucose, CMRglu was significantly lower in the elderly as compared with young subjects and significantly higher in females relative to males. However, in 58 of these subjects who also had magnetic resonance imaging scans, age and gender were found to be unrelated to CMRglu, when the effects of brain volume and brain atrophy on CMRglu were partialed out using covariate analyses. Individually, brain volume was found to have a significant effect on CMRglu, explaining approximately 17% of the variability in CMRglu measures and brain atrophy explaining approximately 8% of the variance in CMRglu. Together these two measures accounted for approximately 21% of the variance. Cerebrovascular risk factors in normal subjects were not found to affect mean CMRglu or the variability of CMRglu measures. In this study almost 80% of the variance in CMRglu could not be explained by any of the factors that had been considered. This implies a lack of sensitivity of absolute values of global CMRglu to the mild effects of brain dysfunction. Although some of the unexplained variance is probably methodological in origin, physiological factors that are difficult to quantify, such as the state of arousal, are likely to be contributory as well.

Longitudinal study of the early neuropsychological and cerebral metabolic changes in dementia of the Alzheimer type

To examine the progression of neuropsychologic and metabolic changes in the early stages of dementia of the Alzheimer type (DAT), we studied 11 midly demented patients longitudinally. Three aspects of neuropsychological function were measured: memory, attention to complex sets and abstract reasoning, and lateralized functions, i.e., language and visuoconstruction. Regional cerebral metabolic rates for glucose were measured in frontal, parietal, and temporal association cortices. Our results show that, in general, memory deficits are the first neuropsychological impairments to occur in DAT, followed by problems with attention to complex cognitive sets and abstract reasoning, which are followed in turn by deficits in language and visuospatial abilities. In addition, neocortical metabolic abnormalities usually precede impairment of neocortically mediated attention and abstract reasoning by 8 to 16 months, and precede impairment of neocortically mediated language and visuospatial function by 12 to 37 months. These findings suggest that the first nonmnestic neuropsychological consequence of neocortical physiological dysfunction in DAT is a loss of attentional capacity. Since neocortical metabolic changes generally precede the appearance of neocortically mediated neuropsychological dysfunction, physiologic dysfunction may exist for some time before cognition is affected.

Experimental approaches to age-related cognitive impairments

Rats exhibit morphological, biochemical, and metabolic changes in their brains, as well as cognitive deficits, with aging. Aged rats were found to be significantly impaired compared to young rats in a water maze task and test of motor coordination, and show reduced locomotor activity and exploration. Although aged rats did exhibit deficits as a group, not all aged rats were impaired. Additionally, the subgroup that was impaired on one task was not necessarily the subgroup that was impaired on another task. The cholinergic projection neurons in the basal forebrain region were significantly atrophied in the aged rodent. The degree of atrophy was highly correlated with the cognitive impairment exhibited on the Morris water maze task. Swollen choline acetyltransferase (ChAT)-positive "plaque-like" structures were observed in the neocortex of the aged but not the young rats. Declines in cholinergic activity in the brain has also been observed during aging. Biochemical measurements of ChAT in the basal forebrain region of aged rats revealed small but consistent decreases in ChAT activity compared to young rats. General metabolic activity, measured by the 2-deoxyglucose method, was also decreased in the hippocampal CA1 and CA3 fields, the dentate gyrus, the medial septal-diagonal band area, and the prefrontal cortex of aged rats. There was a significant correlation between the decrease in glucose utilization and deficits on the Morris water maze. Most aged rats exhibit pathological EEG patterns as reflected by frequent long-duration high voltage neocortical spindles (HVS) during immobility. Bilateral lesions of the nucleus basalis and scopolamine treatment increased the incidence of HVS, thereby mimicking changes in the aged brain. We attempted to ameliorate the cognitive deficits observed in subgroups or impaired rats by either: (1) implanting fetal cells of basal forebrain origin into the hippocampus, or (2) infusing nerve growth factor (NGF) chronically into the lateral ventricle. The grafts appeared to facilitate an improvement in the ability of the impaired aged rats to perform in the Morris water maze. This improved performance was reversed by injections of atropine at doses that did not affect the behavior of young animals that performed well in the same task. These results suggest that enhancement of the cholinergic system could have an effect on the performance of the impaired aged animals. The study of the effects of infusions of NGF clearly demonstrate that the ability of impaired aged rats to remember what they had previously learned was increased after NGF treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Reproducibility of cerebral glucose metabolic measurements in resting human subjects

Positron emission tomography with 11C-2-deoxyglucose was used to determine the test-retest variability of regional cerebral glucose metabolism in 22 young normal right-handed men scanned twice in a 24-h period under baseline (resting) conditions. To assess the effects of scan order and time of day on variability, 12 subjects were scanned in the morning and afternoon of the same day (a.m.-p.m.) and 10 in the reverse order (p.m.-a.m.) with a night in between. The effect of anxiety on metabolism was also assessed. Seventy-three percent of the total subject group showed changes in whole brain metabolism from the first to the second measurement of 10% or less, with comparable changes in various cortical and subcortical regions. When a scaling factor was used to equate the whole brain metabolism in the two scans for each individual, the resulting average regional changes for each group were no more than 1%. This suggests that the proportion of the whole brain metabolism utilized regionally is stable in a group of subjects over time. Both groups of subjects had lower morning than afternoon metabolism, but the differences were slight in the p.m.-a.m. group. One measure of anxiety (pulse at run 1) was correlated with run 1 metabolism and with the percentage of change from run 1 to run 2. No significant run 2 correlations were observed. This is the first study to measure test-retest variability in cerebral glucose metabolism in a large sample of young normal subjects. It demonstrates that the deoxyglucose method yields low intrasubject variability and high stability over a 24-h period.

PET determination of regional cerebral glucose metabolism in alcohol-dependent men and healthy controls using 11C-glucose

Regional brain glucose metabolism was determined in 9 male alcohol-dependent inpatients and 12 male healthy controls. All the patients were socially impaired by the alcohol abuse. All the subjects had abstained from alcohol and drugs for more than four weeks before entering the study. Brain glucose metabolism was determined by positron emission tomography (PET) with 11C-glucose as the tracer. Regions of interest were drawn on displayed computed tomographic (CT) images of the brain. Regions were transferred to corresponding PET slices, allowing the determination of regional glucose metabolism. In the healthy volunteers there was a reduction in glucose metabolism with age. In 11 of the 19 brain regions examined, the alcoholics had a 20% to 30% lower glucose metabolism than the controls. This was true for both cortical and subcortical structures. The distribution of relative regional metabolic rates indicated that parietal cortical areas were most affected. Atrophic changes as shown by CT were not correlated to the reduced metabolism in the alcohol-dependent patients.

Imaging local cerebral blood flow by Xenon-enhanced computed tomography--technical optimization procedures

Methods are described for non-invasive, computer-assisted serial scanning throughout the human brain during eight minutes of inhalation of 27%-30% Xenon gas in order to measure local cerebral blood flow (LCBF). Optimized Xenon-enhanced computed tomography (XeCT) was achieved by 5-second scanning at one-minute intervals utilizing a state-of-the-art CT scanner and rapid delivery of Xenon gas via a face mask. Values for local brain-blood partition coefficients (L lambda) measured in vivo were utilized to calculate LCBF values. Previous methods assumed L lambda values to be normal, introducing the risk of systematic errors, because L lambda values differ throughout normal brain and may be altered by disease. Color-coded maps of L lambda and LCBF values were formatted directly onto CT images for exact correlation of function with anatomic and pathologic observations (spatial resolution: 26.5 cubic mm). Results were compared among eight normal volunteers, aged between 50 and 88 years. Mean cortical gray matter blood flow was 46.3 +/- 7.7, for subcortical gray matter was 50.3 +/- 13.2 and for white matter was 18.8 +/- 3.2. Modern CT scanners provide stability, improved signal to noise ratio and minimal radiation scatter. Combining these advantages with rapid Xenon saturation of the blood provides correlations of L lambda and LCBF with images of normal and abnormal brain in a safe, useful and non-invasive manner.

Hemispheric asymmetries, fourth ventricular size, and cerebellar morphology in autism

Hemispheric asymmetries, fourth ventricular size, and cerebellar morphology were examined in 15 healthy men, aged 18 to 39 years, with documented childhood diagnoses of infantile autism, and in 20 healthy age- and sex-matched controls using computerized transverse axial tomography (CT). Nine patients were of approximately average intelligence, 3 showed specific language impairments, and 3 were mentally retarded. No significant group differences were seen in the distributions of frontal or posterior asymmetries of width or petalia. No subject showed evidence of cerebellar atrophy or an enlarged fourth ventricle. These results fail to support a hypothesis of unusual hemispheric asymmetry or macroscopic abnormalities of the posterior fossa in autism.

Positron emission tomography with the deoxyglucose technique and the diagnosis of Alzheimer's disease

Riege and Metter provide a useful review of the application of PET in the evaluation of Alzheimer's disease (AD). We share their enthusiasm for continued support and development of tools to image metabolic processes. Our commentary focuses on neuroimaging and the diagnosis of AD and introduces some new data that directly impacts on the interpretation of PET-2-deoxyglucose (2DG) data.

Cognitive and brain imaging measures of Alzheimer's disease

Diagnosis of Alzheimer's disease (AD) during life relies upon clinical and neurobehavioral symptoms but is presumptive without microscopic verification of neuropathology. Studies in this review observed considerable heterogeneity in AD symptoms and did not agree on how to detect the earliest symptoms. Problems exist in diagnosis. Differences in symptoms and diagnosis result from how AD is defined neurobehaviorally and on the model used for description. The studies reviewed have been considered under three basic models: A severity (staging) model; a heterogeneity (subtyping) model; and an information processing model. Differences in model intent have resulted in differences in disease description. Brain imaging measures have not invalidated models but add the neural substrate needed to examine correlation of measures within each model.

Regional brain glucose metabolism in drug free schizophrenic patients and clinical correlates

Regional brain glucose metabolism was investigated in healthy volunteers (n = 10) and in drug free schizophrenic patients (n = 20). The metabolism was determined by positron emission tomography (PET) with 11C-glucose as the tracer. Diagnosis of schizophrenia was made according to RDC and DSM III. Eight patients had their first psychotic episode, four patients had a subchronic course and eight patients had a chronic course with an exacerbation of their illness. Computed tomography (CT) of the brain were made in all the subjects. Regions of interest (n = 35) were drawn on displayed CT images and the marked regions were transferred to the corresponding slice of the PET examination. The PET investigation was made in a dimly lit, quiet room with the eyes of the subject covered. The time course of the 11C-glucose uptake was measured by a four ring PET scanner (PC-384-7B). Metabolic rates of glucose varied greatly among the schizophrenic patients investigated. The variance was significantly greater than that of the controls in most regions. Decreases in mean levels of metabolic rates were related to patients with subchronic or chronic courses. Changes in metabolism were not related to previous duration of neuroleptic treatment of the patients. Left-right asymmetries were found in the temporal lobe (area 22) and the basal frontal cortex (area 11), the metabolic rates of the patients being lower on the left side compared to the controls. Asymmetry of the metabolic rate of the amygdala in hebephrenic patients was the opposite of that found in paranoid patients and controls. Negative correlations between regional metabolic rates and autistic or negative symptoms were found. Thus, the lower the metabolic rate was, the more autistic the patient. Metabolic rates were not correlated to atrophic changes of the brain. No basis for a specific alteration in frontal cortical metabolism of schizophrenics was obtained. Changes in regional metabolic rates in schizophrenia are suggested to reflect disturbances in more general mechanisms which are of importance in neuronal function.

Scaled subprofile model: a statistical approach to the analysis of functional patterns in positron emission tomographic data

The data obtained from measurements of regional rCMRglu using [18F]fluorodeoxyglucose (FDG)/positron emission tomographic (PET) data contain more structure than can be identified with group mean rCMRglu profiles or regional correlation coefficients. This additional structure is revealed by a novel mathematical-statistical model of regional metabolic interactions that explicitly represents rCMRglu profiles as a combination of region-independent global effects, a group mean pattern and a mosaic of interacting networks. In its application to FDG/PET data, this model removes global subject effects [global scaling factors (GSFs)] and a group mean pattern (profile) so as to maximize statistical power for the detection and simultaneous discovery of all networks of two or more regions that form a significant and consistent linearly covarying pattern. The model approach presented here was applied to the combined rCMRglu data from 12 demented AIDS patients and 18 normal controls: Two significant metabolic covariance pattern descriptors that together accounted for 71 to 96% of the rCMRglu/GSF variation across subjects for 22/28 regions in the AIDS group were extracted. Each descriptor was found to be highly correlated with performance on several neuropsychological tests, providing independent validation of the analysis technique as a means of discovering and describing behaviorally related components of group rCMRglu profiles.

Cerebrospinal fluid monoamines in Down's syndrome adults at different ages

Markers of monoamine metabolism in lumbar cerebrospinal fluid (CSF) and plasma were determined in nine young, healthy adults with trisomy 21 Down's syndrome (DS), 21-34-years-old, and in three DS subjects over 45 years, two of whom were demented, as well as in two groups of age-matched controls. Test scores of general intelligence, visuospatial ability, visual discrimination and verbal intelligence were reduced significantly in the old as compared to the young DS subjects. Dementia in DS was evident from a history of mental deterioration, disorientation and hallucinations. In the young DS adults, as compared to the controls, CSF 5-HIAA and norepinephrine were significantly elevated but plasma levels were unchanged. HVA, MHPG and biopterin did not differ between the DS groups and age-matched controls, or with relation to age in the DS or control subjects. These results suggest an increased turnover of monoamines in young adults with DS but that alterations in monoamine metabolism are unrelated to the cognitive decline with age in DS.

Topographical analysis of glucose metabolism, as measured with positron emission tomography, in dementia of the Alzheimer type: use of linear histograms

A linear histogram method was employed to analyze brain images of glucose uptake obtained by positron emission tomography in patients with dementia of the Alzheimer type and in control subjects. A line was drawn by computer which traversed the image of a brain slice taken at 70 mm above and parallel to the inferior orbitomeatal line, and rCMRglc was plotted as a function of distance along this line in 3 brain areas: frontal, sensorimotor and parietal. Peak rCMRglc values were significantly decreased in moderately-to-severely demented patients relative to healthy age-matched controls, but not in mildly demented patients. Furthermore, both the mildly and the more severely demented patients differed from controls in having reduced ratios of parietal association to sensorimotor peak rCMRglc. The variances of right-left metabolic asymmetries did not differ significantly between Alzheimer patients and controls. Severity of dementia, as evaluated by scores on the Mini-Mental State Examination, correlated with ratios of peak rCMRglc in frontal and parietal cortex to that in sensorimotor cortex. These results indicate that measures of focal peak rCMRglc do not discriminate between mildly demented patients and controls, whereas focal ratios of rCMRglc, where the denominator corresponds to rCMRglc from a relatively spared region, provide useful measures of metabolic dysfunction in the early stages of Alzheimer's disease.

Positron emission tomography studies of normal aging: a replication of PET III and 18-FDG using PET VI and 11-CDG

Using PET VI and 11-CDG we replicated our earlier PET III and 18-FDG normal aging findings. Examination of young and old normal volunteers revealed the absence of any absolute regional age-related changes in glucose utilization. For the combined sample (N = 81) we did find evidence to suggest a relative hypofrontal change with increasing age. A strong relationship between age and ventricular size (CT) was also found. These findings suggest the preserved glucose metabolism of the resting aging brain in the presence of structural atrophic changes.

Relation of measured brain glucose utilisation and cerebral atrophy in man

The effect of cerebral atrophy on measured cerebral metabolic rates for glucose (CMRglc), as determined with positron emission tomography (PET), was examined in 49 healthy males aged 21-83 years. Global CMRglc and regional CMRglc for 34 grey matter regions parallel to and from 30 to 80 mm above the inferior orbital meatal (IOM) line were measured under resting conditions, using [18F]-fluorodeoxyglucose and an ECAT II positron emission tomograph. Using a GE 8800 CT/T scanner, slices parallel to and from 30 to 80 mm above the IOM line were analysed for CSF volume. Cerebral atrophy, indicated by increased CSF volume, was correlated significantly with global CMRglc, but accounted for no more than 13% of the variance in the CMRglc measurements. Methods for correcting for inter-subject variation in CSF volume were proposed. Global values for CMRglc, uncorrected or corrected for CSF volume, were found to be age invariant. These findings indicate that (a) cerebral atrophy has a small, but statistically significant effect on CMRglc as measured with PET; (b) CMRglc is age invariant in healthy males.

Decline in cerebral glucose utilisation and cognitive function with aging in Down's syndrome

The cerebral metabolic rate for glucose (CMRglc) was measured with positron emission tomography and [18F]2-fluoro-2-deoxy-D-glucose in 14 healthy subjects with Down's syndrome, 19 to 33 years old, and in six healthy Down's syndrome subjects over 35 years, two of whom were demented. Dementia was diagnosed from a history of mental deterioration, disorientation and hallucinations. All Down's syndrome subjects were trisomy 21 karyotype. CMRglc also was examined in 15 healthy men aged 20-35 years and in 20 healthy men aged 45-64 years. All subjects were at rest with eyes covered and ears plugged. Mean hemispheric CMRglc in the older Down's syndrome subjects was significantly less, by 23%, than in the young Down's syndrome group; statistically significant decreases in regional metabolism (rCMRglc) also were present in all lobar regions. Comparison of the younger control group with the older control group showed no difference in CMRglc or any rCMRglc (p greater than 0.05). Assessment of language, visuospatial ability, attention and memory showed significant reductions in test scores of the old as compared with the young Down's syndrome subjects. These results show that significant age differences in CMRglc and rCMRglc occur in Down's syndrome but not in healthy controls, and that, although only some older Down's syndrome subjects are demented, significant age reductions in neuropsychologic variables occur in all of them.

Behavioral activation and the variability of cerebral glucose metabolic measurements

Variability in cerebral glucose metabolism was examined between and within subjects when paired studies were performed in the resting state or in a behaviorally activated state. Both normal and demented subjects were studied twice each, from 1 to 6 weeks apart, under near-identical conditions, using positron emission tomography (PET) and [18F]fluorodeoxyglucose. Resting state studies were repeated in nine normal and four demented subjects. A picture-viewing test, used for activation during PET, was used repeatedly in seven normal and five demented subjects. Within-subject variability, as assessed by the percent difference in metabolic rates in paired studies, was reduced by 60-70% for activation state compared to resting state studies in normals. It is concluded that PET studies of brain metabolism, which are designed to study the active brain, should indeed be performed in functionally activated states, as in addition to demonstrating metabolism during a defined functional state, activation studies show reduced variability of cerebral metabolic measures.

Intercorrelations of regional cerebral glucose metabolic rates in Alzheimer's disease

Patterns of cerebral metabolic correlations were compared between 21 Alzheimer's disease patients and 21 healthy age-matched controls in the resting state. Cerebral metabolic rates for glucose were determined by positron emission tomography using [18F]2-fluoro-2-deoxy-D-glucose. Partial correlation coefficients, controlling for whole brain glucose metabolism, were evaluated between pairs of regional glucose metabolic rates in 59 brain regions. Reliable correlation coefficients were obtained with the 'jackknife' and 'bootstrap' statistical procedures. Compared with healthy controls, the Alzheimer patients had significantly fewer reliable partial correlation coefficients between frontal and parietal lobe regions, and more reliable correlations between the cerebellum and temporal lobe. The number of reliable correlations between many bilaterally symmetric brain regions was reduced in the Alzheimer patients, as compared with controls. These results suggest that in the early stages of Alzheimer's disease there is a breakdown of the organized functional activity between the two cerebral hemispheres, and between parietal and frontal lobe structures.

Cerebral metabolism, anatomy, and cognition in monozygotic twins discordant for dementia of the Alzheimer type

One pair of monozygotic twins discordant for dementia of the Alzheimer type (DAT) was studied using neuropsychological testing, quantitative x-ray computed tomography (QCT) and magnetic resonance imaging (MRI) of the brain. Cerebral glucose metabolism was measured using positron emission tomography (PET) and 2-[18-F]fluoro-2-deoxy-D-glucose (FDG). The affected twin had a seven year history of progressive cognitive impairment and was severely demented. Neuropsychological testing of the affected twin demonstrated marked deficits in all areas of cognitive function. The asymptomatic twin showed some impairment on tests of perceptual organisation and delayed recall. The affected twin had loss of gray matter and ventricular enlargement on QCT and MRI compared with healthy controls (p less than 0.05). He also had frontal and parietal lobe hypometabolism and increased asymmetry of metabolism on PET compared to both his twin and healthy age-matched controls (p less than 0.05). PET, QCT, and MRI distinguished changes in the twin with DAT compared with his brother and healthy controls. Although the subtle neuropsychological abnormalities of the asymptomatic twin may be signs of early DAT, they were not accompanied by any changes in regional cerebral metabolism or brain structure.

Cerebral glucose metabolism in five patients with Lennox-Gastaut syndrome

Regional cerebral glucose metabolic rates were estimated by positron emission tomography, in parallel with electroencephalography and cranial computed tomography in 5 patients with Lennox-Gastaut syndrome. The 5 patients, 3 boys and 2 girls, ranged in age from 10-15 years. Computed tomography revealed no gross abnormalities. Each patient received 2-5 mCi of 2-(18F)-fluoro-2-deoxy-D-glucose (18F-FDG) intravenously. Averaged cerebral glucose metabolic rates were reduced in each cerebral region as compared with controls. Unilateral hypometabolism was present in 4 patients: one in the inferior frontal gyrus as well as the posterior portion of the superior temporal gyrus; one in the inferior frontal gyrus; one in the posterior portion of the superior temporal gyrus; and one demonstrated diffuse hemispheric hypometabolism including the inferior frontal and posterior portion of the superior temporal gyrus. The side of hypometabolism was the same as the epileptogenic focus on the electroencephalogram. No focal changes were demonstrated on the electroencephalogram of a patient whose positron emission tomography revealed hemispheric hypometabolism. Hypometabolism of the inferior frontal and posterior portion of the superior temporal gyrus may relate to the possible pathogenesis of Lennox-Gastaut syndrome. Positron emission tomography has the potential to reveal a latent focal or lateralized abnormality in some patients with non-localized electroencephalographic changes.

Neuropsychological and cerebral metabolic function in early vs late onset dementia of the Alzheimer type

Differences in age at onset of dementia of the Alzheimer type (DAT) have been associated with differences in cognitive impairments and course of the disease. To investigate this, we examined cerebral metabolism and cognitive performance in early and late onset DAT patients, who had equivalent duration and severity of illness. Regional cerebral metabolic rates for glucose were measured in the resting state by positron emission tomography using [18F]2-fluoro-2-deoxy-D-glucose. A cross-sectional analysis showed no significant differences between the two groups in performance on neuropsychological tests, but the early onset patients showed significantly more parietal metabolic dysfunction than did the late onset patients. Longitudinal analysis showed no significant differences between early and late onset patients in rate of cognitive decline over a mean interval of 19 months. Thus, our results do not support the hypothesis of different subgroups in DAT based on age at onset, nor suggest a faster rate of cognitive decline in younger patients.

Brain glucose metabolism in children with the autistic syndrome: positron tomography analysis

Brain glucose metabolism was measured in 18 autistic children, using high resolution positron emission tomography. Global brain glucose utilization in the autistic population was slightly more elevated than in young adult volunteers but did not differ significantly from that of control children. Regional metabolic maps were also normal, although there was evidence for heterogeneities, particularly at the level of prefrontal and parieto-temporo-occipital association areas: 6 children showed a relative hyperfrontality whilst hypofrontality was found in 2 cases; these heterogeneities were not correlated with clinical symptoms. These data suggest that both the rate and the regional distribution of brain glucose metabolism are normal in autistic children. Variations in terms of relative metabolic rates in association cortex remains to be investigated further.

Reduction in regional cerebral metabolic rate of oxygen during human aging

To investigate changes in cerebral circulation and oxygen metabolism during aging, regional cerebral blood flow (rCBF), regional oxygen extraction fraction (rOEF), regional cerebral metabolic rate of oxygen (rCMRO2) and regional cerebral blood volume (rCBV) were measured using the 15O labelled gas inhalation technique and a multi-slice positron emission tomograph (PET) in 22 healthy volunteers, aged from 26 to 64 years old. The measurements were performed with subjects at rest, without sensory deprivation. The values of rCBF, rOEF, rCMRO2 and rCBV in more than 40 anatomical structures of the brain were evaluated by studying a large series of scans in each region of interest after the functional PET image had been anatomically identified using x-ray computed tomographic images corresponding to the PET. In mean gray values, only CMRO2 showed significant reduction with age. rCMRO2 significantly decreased with age only in the supratentrium, and much more in the left hemisphere. Especially remarkable was rCMRO2 reduction in the left caudate region. Both CBF and OEF were variable and less age-dependent. It was concluded that CMRO2 could be reflecting healthy brain aging most properly.

Relations among age, visual memory, and resting cerebral metabolism in 40 healthy men

Visual memory, as measured by the Benton Visual Retention Test (BVRT), and resting regional cerebral metabolic rates for glucose (rCMRglc), as measured by positron emission tomography (PET) and [18-F]fluorodeoxyglucose, were examined in 40 very healthy men, aged 21 to 83 years. Age-related differences in visual memory were found but were significantly smaller than differences reported in the general population. This discrepancy is attributable to our rigorous health screening. The age-related differences found in this sample are estimates of the lower limit of population differences unconfounded by disease. Age-related differences on undistracted delayed visual memory were greater than differences on immediate visual memory, suggesting age-related differences in spontaneous elaborative visual information processing. No relation between visual memory and resting rCMRglc was found, supporting the hypothesis that mental abilities are unrelated to resting brain metabolism unless both functions are influenced by disease.

Correction of positron emission tomography data for cerebral atrophy

Because positron emission tomography (PET) provides measurements per unit volume of intracranial contents, these measurements may be affected by the inclusion of metabolically inactive CSF spaces in the volume in which they are made. Thus, PET measurements of CBF and metabolism may be artifactually lowered in normal aging and dementia, which are both associated with significant brain atrophy. We describe a method to correct global PET data, averaged over several tomographic slices, for cerebral atrophy by using measurements of CSF space volume obtained with quantitative x-ray computed tomography. The importance of making such a correction is demonstrated using PET measurements of CBF and oxygen metabolism obtained in normal young, normal elderly, and demented subjects.

Energy metabolism in demented brain

The term dementia refers to a number of very complicated disorders of the brain with several morphological, biochemical and functional alterations. Several alterations occur in Alzheimer's disease. They include alteration in neurotransmitters related substances and changes in brain metabolic rate. Changes in metabolic activity are among the earliest and best documented of all modification reported in Alzheimer's brain. They appear to be correlate with the severity of the disease, and to be more marked in specific areas of the brain which appear to be clinically more involved. In this report will be discussed the observations on changes of cerebral glucose metabolic rate, cerebral oxygen consumption, cerebral blood flow reported in vivo in demented patients. The observations of changes in energy metabolism related enzymes and the relationship between these changes and those in neurotransmitters related substances will be also reviewed.

Senile dementia and Alzheimer's disease. Brain blood flow and metabolism

Dementia of Alzheimer type is not form of accelerated aging. Blood flow, oxygen consumption and glucose utilization of the normally aged brain are maintained unchanged from the 3rd to the 7th decade of life. Thereafter, these parameters may decrease. Brain blood flow and oxidative metabolism is reduced in dementia of Alzheimer type and thus is different from the aged-matched mentally healthy subjects. There is evidence that the predominant impairment among these parameters may occur in cerebral glucose metabolism. This disturbance may precede changes in cerebral oxygen consumption and blood flow. Cerebral hypometabolism of glucose is accentuated in the temporo-parietal cortex. This finding may be helpful in diagnosing dementia of Alzheimer type.

Cerebral metabolism as measured with positron emission tomography (PET) and [18F] 2-deoxy-D-glucose: healthy aging, Alzheimer's disease and Down syndrome

Brain metabolism has been measured with positron emission tomography and 18[F] fluoro-2-deoxyglucose. Brain metabolic function remains age invariant in healthy aged subjects 21 to 83 years. Brain metabolism remains unchanged in the mild-moderate severity Alzheimer's disease group and significantly reduced throughout the brain in the late-severe form. Serial assessments over 2 1/2 years of brain metabolic function in an Alzheimer's disease subject with positron emission tomography and 18[F]-fluoro-2-deoxyglucose revealed initial reductions in the parietal lobe and regions prior to neuropsychological changes. Marked elevations in brain metabolism were found in young adult Down syndrome subjects while age-related declines were found in the middle aged (non-demented) Down syndrome subjects and further reductions in the demented Down syndrome individuals.

Age differences in intercorrelations between regional cerebral metabolic rates for glucose

Patterns of cerebral metabolic intercorrelations were compared in the resting state in 15 healthy young men (ages 20 to 32 years) and 15 healthy elderly men (ages 64 to 83 years). Controlling for whole-brain glucose metabolism, partial correlation coefficients were determined between pairs of regional cerebral metabolic rates for glucose determined by positron emission tomography using [18F]fluorodeoxyglucose and obtained in 59 brain regions. Compared with the young men, the elderly men had fewer statistically significant correlations, with the most notable reductions observed between the parietal lobe regions, and between the parietal and frontal lobe regions. These results suggest that cerebral functional interactions are reduced in healthy elderly men.

Abnormalities of regional brain metabolism in Alzheimer's disease and their relation to functional impairment

Resting brain metabolism in patients with Alzheimer's disease (AD) has consistently been demonstrated to be reduced. Moreover, the magnitude of the reduction is related to the severity of dementia. Positron emission tomography (PET), which provides regional metabolic rates for glucose in cross-sectional slices of brain, has demonstrated three alterations in AD that are related to functional deficits. First, whole brain metabolic rate is reduced, and these reductions are related to overall severity of dementia. Second, regional metabolic rates in the association cortices demonstrate relatively greater reductions than are observed in the primary sensory and motor cortices, corresponding to marked impairment of higher cognitive function and relative sparing of sensory and motor function. Third, regional metabolic rates in the association cortices demonstrate increased left-right asymmetry relative to controls. Greater metabolic asymmetry is accompanied by disproportionate neuropsychological deficits in either language or visuospatial function, depending on whether the left or right cerebral hemisphere, respectively, has a lower metabolic rate.

Standardized mean regional method for calculating global positron emission tomographic measurements

A new "mean regional" method for calculating global hemispheric values of blood flow, blood volume, and metabolism with positron emission tomography is presented. It is based on a standardized set of regions defined according to coordinates in a stereotactic atlas of the brain. Region locations in each individual scan were determined by a localization technique that is independent of the appearance of the physiological images. Measurements obtained with this mean regional method minimize contributions from nonbrain structures such as ventricles or venous sinuses and provide the necessary basis for comparisons among different subjects and laboratories.

Clinical history, brain metabolism, and neuropsychological function in Alzheimer's disease

Data concerning 7 patients with a diagnosis of presumptive Alzheimer's disease (mean age, 65.6 years) are presented in detail in relation to the patients' regional cerebral metabolic rates for glucose. Rates were measured by positron emission tomography with fluorine 18-labeled fluoro-2-deoxy-D-glucose under conditions of reduced visual and auditory stimulation. A relationship was found between severity of dementia and brain metabolism. In patients with mild to moderate Alzheimer's disease, memory and intellectual deficits were evident without major reductions in absolute metabolic rates, while ratios of regional to whole brain metabolism revealed reductions in regions of the parietal lobes. In the late, severe form of the disease, brain metabolic rates were consistently and significantly reduced. The findings suggest that memory and intellectual deficits are reflected in reductions of brain metabolism in some brain regions in mild to moderate forms of Alzheimer's disease and that, in the late, severe form of the disease, reductions occur consistently throughout the brain.

Relations between neuropsychological and cerebral metabolic asymmetries in early Alzheimer's disease

Regional CMRglc (rCMRglc) values were determined with positron emission tomography (PET) in 10 patients with mild to moderate clinically diagnosed Alzheimer's disease (AD) and in 26 healthy controls. rCMRglc in frontal, parietal, and temporal association cortices were significantly more laterally asymmetrical in AD patients than in controls (p less than 0.05). Furthermore, lateral asymmetry of rCMRglc in AD patients but not in the control subjects correlated significantly with asymmetry of language and visuospatial functions such that lower left than right rCMRglc was associated with relatively greater impairment of language and vice versa. The results demonstrate that discrepancies between language and visuospatial deficits in patients with early AD are related to asymmetrical reductions in cerebral cortical glucose metabolism.