Human brain glucose utilization and cognitive function in relation to age

Healthy aging, memory subsystems and regional cerebral oxygen consumption

The present study was designed to search for concomitant age-related changes in memory subsystems, defined according to current structural theories, and resting oxygen consumption in selected brain regions. We have investigated a sample of subjects between 20 and 68 years of age and strictly screened for their good health. We applied in the same subjects a battery of neuropsychological tests selected to investigate several memory subsystems, and high-resolution positron imaging with stereotaxic localization to study a purposely limited number of cerebral structures, selected on a priori hypotheses to match the different memory subsystems. Our results showed significant age-related changes in performance on some tests, consistent with the literature, including an increase in semantic memory and a decrease in both working memory (central executive system) and verbal episodic and explicit memory. There was also an age-related linear decrease in global brain oxygen consumption which regionally reached statistical significance for the neocortical areas and the left thalamus. There was a limited number of significant, age-independent correlations between the raw psychometric test scores and resting regional oxidative metabolism. Consistent with our present understanding of the functional anatomy of memory, the Associate Learning scores (verbal episodic and explicit memory) were positively correlated with left hippocampal and thalamic metabolism. The positive relationships found between right hippocampal metabolism and performance in the Associate Learning and the Brown-Peterson tests were less expected but would be consistent with findings from recent PET activation studies. The results from this investigation are discussed in the light of current knowledge concerning the neuropsychology and the neurobiology of both aging and memory.

Reduced temporal lobe glucose metabolism in aging

The results of a positron emission tomography study of regional cerebral metabolic rates of glucose are reported for 8 healthy old subjects (mean age, 66 yr; standard deviation [SD], 5) and 9 young subjects (mean age, 27 yr; SD, 4.6) using a high-resolution positron emission tomograph and the glucose metabolic tracer 18F-fluorodeoxyglucose. Older subjects showed significantly lower cerebral metabolic rates than did the young subjects, in anterior, middle, and posterior temporal neocortex and in mesial temporal cortex, with the largest differences occurring in anterior temporal cortex (temporal pole). The current findings may reflect either decreases in regional cerebral metabolic rates for glucose that occur with normal aging, or early indications of cognitive dysfunction that is associated with age-related disorders.

Memory Self-Appraisal and Cerebral Glucose Metabolism in Age-Associated Memory Impairment

The authors used positron emission tomography to measure cerebral glucose metabolism in 43 people with age-associated memory impairment to determine relationships between memory self-appraisal and brain function. People with lower frontal metabolism during a resting state reported more frequent prior mnemonics usage, a measure of memory self-appraisal. A multiple regression analysis indicated that reported mnemonics usage was the most significant predictor of left (P = 0.0004) and right (P = 0.0014) frontal metabolism. These models indicated that mnemonics usage, along with depression ratings, accounted for 39% of left frontal lobe function and, along with visual spatial memory, accounted for 40% of right frontal metabolism. These results suggest that mnemonics usage may compensate for subtle frontal dysfunction or reflect greater efficiency of memory processing.

Sex differences in patterns of hemispheric cerebral metabolism: a multiple regression/discriminant analysis of positron emission tomographic data

Sex differences in brain hemispheric structure and function have been reported, and sex-related differences in hemispheric interregional correlations were reported in a prior analysis of resting PET glucose metabolic (rCMRglc) data. To explore further the effect of sex on patterns of hemispheric brain functional interactions, we applied a multiple regression/discriminant analysis to resting rCMRglc PET data from young normal men and women to test two hypotheses: (1) women have stronger between-hemisphere functional interactions; (2) men have stronger within-hemisphere functional interactions. Two separate discriminant functions based on these hypotheses distinguished men and women: the first reflected rCMRglc interdependencies between hemispheres and correctly classified all women and 94% of the men; the second reflected rCMRglc interdependencies within the left hemisphere and correctly classified 82% of the women and 88% of the men. Because the discriminant functions successfully distinguished men and women, these results provide support for both hypotheses.

Differential effects of mood on cortical cerebral blood flow: a 133xenon clearance study

Studies of healthy and clinical populations have suggested valence-specific cortical and subcortical neural systems regulating emotions. In a study of 12 normal volunteers, the 133xenon clearance method for measuring regional cerebral blood flow (CBF) was used to study the effects of experimentally controlled mood states on regional brain activity within superficial cortex. CBF was measured with 254 detectors and bolus infusion during a happy mood induction task, a sad mood induction task, a sex differentiation task, and a resting baseline condition. CBF increased during sad and decreased during happy mood induction, relative to the activated (sex differentiation) and the nonactivated (resting) nonemotional control conditions. Increased CBF during sad mood induction was correlated with greater negative mood changes. Conversely, increased CBF was associated with a stronger subjective experience of positive affect during happy mood induction. This suggests that cortical arousal may serve to intensify the conscious experience of emotion. Heart rate accelerated during happy and sad mood induction and during sex differentiation relative to a pretask baseline condition. Some regional specificity of effects was also observed. The occipital temporal region showed higher overall CBF during sad mood induction than during happy mood induction. The only region that showed specific lateralized changes in CBF which differentiated sad from happy states was the frontal pole, with left CBF being higher during sad and lower during happy mood induction relative to right CBF. For sad mood induction, there were significant regional differences among correlations between CBF and self-ratings. These were attributable to higher negative correlations (i.e., higher CBF correlates with negative self-rating) in midtemporal, occipital temporal, and postcentral regions. These correlations did not vary across the 15 regions for happy mood induction. For sad mood induction, heart rate correlated positively with CBF increase and with negative affect. Correlations were opposite for happy mood induction. The results suggest high cortical and autonomic arousal during negative/sad mood and low cortical and high autonomic arousal during positive/happy mood. They underscore the value of integrating emotional experience with physiologic measures in neuroimaging activation studies.

Physical Activity, Age, and Cognitive-Neuropsychological Function

Findings from three research paradigms that employed aerobic exercise as an independent variable were used to test the hypothesis that aerobic exercise improves cognitive-neuropsychological functioning. The research paradigms were animal intervention studies, cross-sectional human studies, and human intervention studies. Results from studies of animals, usually rodents, provide consistent evidence that aerobic fitness is associated with improved neurobiological and behavioral functioning. Cross-sectional studies with humans indicate a strong positive association between physical activity level and cognitive-neuropsychological performance. However, results from these studies must be interpreted cautiously, as individuals who elect to exercise or not exercise may differ on other variables that could influence cognitive-neuropsychological performance. To date, human intervention studies have not consistently demonstrated cognitive-neuropsychological improvements following exercise training. To satisfactorily test the exercise/cognition hypothesis with humans, carefully controlled intervention studies that last longer than those previously employed are needed.

Effects of aging on event-related brain potentials (ERPs) in a visual detection task

Event-related brain potentials (ERPs) were recorded from 74 subjects (45 men) between 18 and 82 years of age in a simple visual detection task. On each trial the subject reported the location of a triangular flash of light presented briefly 20 degrees laterally to the left or right visual field or to both fields simultaneously. ERPs to targets exhibited a similar morphology including P1, N1, P2, N2, and P3 components across all age groups. The principal effects of advancing age were (1) a marked reduction in amplitude of the posterior P1 component (75-150 latency) together with an amplitude increase of an anterior positivity at the same latency; (2) an increase in amplitude of the P3 component that was most prominent over frontal scalp areas; and (3) a linear increase in P3 peak latency. These results extend the findings of age-related changes in P3 peak latency and distribution to a non-oddball task in the visual modality and raise the possibility that short-latency ERPs may index changes in visual attention in the elderly.

Longitudinal study on oral health in subjects with Alzheimer's disease

OBJECTIVE

To examine longitudinal oral health changes in unmedicated, generally healthy subjects with Alzheimer's disease (AD) and compare them to age- and gender-matched healthy, unmedicated control subjects.

DESIGN

Oral health parameters were evaluated over 2 to 3 years and the results compared between subjects with AD and controls.

SETTING

Clinical Center of the National Institutes of Health, Bethesda, Maryland.

PARTICIPANTS

Twenty-one community-dwelling subjects with a clinical diagnosis of AD and 21 age- and gender-matched control subjects. Neither population was being treated for any other systemic condition nor taking any prescription medications.

MEASUREMENTS

Unstimulated and stimulated major salivary gland flow rates were measured, and gingival, periodontal, dental, and oral mucosal tissues assessed.

MAIN RESULTS

In general, subjects with AD demonstrated decreased salivary flow rates and diminished oral health, but most longitudinal changes in oral health status were not significantly different than controls.

CONCLUSIONS

Patients with AD are susceptible to a variety of oral health problems, and progression of AD can lead to a deterioration in oral health and function. These patients require aggressive preventive care to maintain function for as long as possible, which necessitates close cooperation among numerous health care professionals.

Clinical studies in Alzheimer patients with positron emission tomography

Brain imaging techniques will in the future play an important role in the assessment of patients with neurogenerative disorders such as Alzheimer's disease (AD). An early diagnosis of AD is today hampered by lack of reliable diagnostic markers. Positron emission tomography (PET) permits the quantification and three-dimensional imaging of physiological variables. This provides the clinician with a non-invasive imaging technique which allows in vivo quantification of physiological processes in AD underlying dysfunction of cognition. PET studies regarding changes in cerebral blood flow and metabolism are rather consistent at least in moderate/advanced cases of AD. How early in the progress of the disease deficits in these parameters can be observed is still an open question. Longitudinal studies will here be important and especially in individuals with a family history of AD. Since deficits in cholinergic neurotransmission have been measured in autopsy AD brains attempts have also been made to visualized cholinergic activity in vivo. Nicotinic and muscarinic receptors have been visualized in normal and AD brains. A reduced uptake and binding of [11C]nicotine in the temporal and frontal cortices have been measured in AD patients by PET. Few treatment studies in AD have been evaluated by PET. Long-term treatment with the cholinesterase inhibitor tacrine increase the uptake of [11C]nicotine. Significant reduction in uptake between the two enantiomers (S)(-) and (R)(+)-[11C]nicotine has been observed compatible with a restoration of nicotinic receptors. Tacrine also significantly increased the glucose metabolism. PET studies indicate that long-term tacrine treatment in AD patients with mild dementia improves functional activities in brain. When an AD patient with moderate dementia was treated with nerve growth factor (NGF) PET studies revealed increase in cortical blood flow and nicotinic receptors. PET studies will in the future play an important role in the evaluation of new therapeutic drug strategies in AD.

Age-related changes of spontaneous EEG described by equivalent dipoles

One of the most commonly used methods for quantification of an EEG is Fast Fourier Transformation (FFT), which suffers from some serious disadvantages, for example: FFT-power data are highly dependent on the choice of reference and thus the topographical distribution of FFT-power data varies according to the used reference. Novel methods which partly resolve this problem have been developed. These methods provide unambiguous data in the frequency domain with regard to reference. In comparison to conventional FFT-power data this approach allows to a higher degree to draw topographical valid conclusions regarding brain function. The aim of the present study on brain electrical activity, using the method of FFT approximation, was to investigate age-related alterations of brain function in carefully screened healthy subjects. The major finding was that, except for a more superficially located beta-activity of higher strength with increasing, age no age-related changes in electrical brain activity were observed.

Early detection of Alzheimer's disease: a statistical approach using positron emission tomographic data

Correlational analysis of regional cerebral glucose metabolism (rCMRglc) obtained by high-resolution positron emission tomography (PET) has demonstrated reduced neocortical rCMRglc interactions in mildly/moderately demented patients with probable Alzheimer's disease (AD). Thus, identification of individual differences in patterns of rCMRglc interactions may be important for the early detection of AD, particularly among individuals at greater risk for developing AD (e.g., those with a family history of AD). Recently, a statistical procedure, using multiple regression and discriminant analysis, was developed to assess individual differences in patterns of rCMRglc interdependencies. We applied this new statistical procedure to resting rCMRglc PET data from mildly/moderately demented patients with probable AD and age/sex-matched controls. The aims of the study were to identify a discriminant function that would (a) distinguish patients from controls and (b) identify an AD pattern in an individual at risk for AD with isolated memory impairment whose initial PET scan showed minor abnormalities, but whose second scan showed parietal hypometabolism, coincident with further cognitive decline. Two discriminant functions, reflecting interactions involving regions most involved in reduced correlations in probable AD, correctly classified 87% of the patients and controls, and successfully identified the first scan of the at-risk individual as AD (probability > 0.70). The results suggest that this statistical approach may be useful for the early detection of AD.

Cerebral blood flow in patients with dementia of Alzheimer's type

In the normal brain as well as in Alzheimer's disease (AD), regional cerebral blood flow (CBF) is coupled to metabolic demand and, therefore, changes in CBF reflect variations in neuronal metabolism. The use of radionuclide techniques, such as positron emission tomography (PET) and single photon emission computed tomography (SPECT), provides an accurate assessment of regional functional activity, i.e., CBF and metabolism, and could be very helpful for the differential diagnosis of AD. This disease is characterized by a decrease in global CBF and metabolism. When found, a symmetric bi-parieto-temporal CBF reduction is highly diagnostic for AD, despite the fact that a similar CBF pattern could also be observed in other types of dementia. Many AD patients with parieto-temporal flow reduction also have a diffuse flow reduction in the frontal cortical areas, particularly in advanced stages of the disease. Lateral CBF asymmetry is also very frequent; speech disorders are highly characteristic of left-sided flow reduction, while visuospatial apraxia is dominating in the right-sided cases. In advanced and severe cases of AD, CBF and metabolism tend to be more uniformly reduced throughout the cortex, sparing only the primary visual and sensory-motor cortices. PET and SPECT measurement of brain perfusion and metabolism has added a new dimension to the knowledge of dementia disorders, with a better differential diagnosis between AD and other forms of dementia. The correlation with neuropsychological data has also given new insight into the disease.

Plasma and cerebrospinal fluid neurochemical pattern in Menkes disease

Menkes disease is a neurodegenerative disorder of copper metabolism. Because the enzyme dopamine-beta-hydroxylase requires copper to catalyze the conversion of dopamine to norepinephrine, we reasoned that patients with Menkes disease would have a neurochemical pattern similar to that seen in patients with congenital absence of dopamine-beta-hydroxylase, i.e., high levels of dopamine, the dopamine metabolite dihydroxyphenylacetic acid (DOPAC), and the catecholamine precursor dihydroxyphenylalanine (DOPA), and low levels of norepinephrine and its neuronal metabolite dihydroxyphenylglycol (DHPG). We measured plasma and cerebrospinal fluid (CSF) levels of catechols in 10 patients ranging in age from 9 days to 27 months. In contrast to patients with congenital absence of dopamine-beta-hydroxylase, norepinephrine levels were normal in plasma of 4 Menkes patients and in CSF of all 10 patients. However, the ratios of DOPA:DHPG and DOPAC:DHPG in plasma and CSF of Menkes patients were invariably increased beyond the ranges of control values. These neurochemical findings indicate partial deficiency of dopamine-beta-hydroxylase in Menkes patients, with compensatory increases in catecholamine biosynthesis in sympathetic nerves and in the brain. Increased tyrosine hydroxylation and increased exocytotic release of norepinephrine may be responsible for preservation of plasma and CSF norepinephrine levels in Menkes patients. The abnormal neurochemical pattern, including high ratios of DOPA:DHPG and DOPAC:DHPG, may serve as a biochemical marker for Menkes disease and provide a baseline against which the influence of proposed therapies can be judged.

Age-dependent cerebral metabolic effects of unilateral nucleus basalis magnocellularis ablation in rats

To investigate the age-dependent functional importance of cholinergic neocortical inputs, and to explore whether cortical cholinergic denervation in aged animals might better model the cerebral metabolic changes of Alzheimer's disease, the effects of unilateral ablation of the nucleus basalis magnocellularis (NBM) on cerebral glucose metabolism were studied in young and aged rats. Regional cerebral metabolic rates for glucose (rCMRglc) were determined, using the [14C]deoxyglucose method, in 48 brain regions of 3- and 24-month old Fischer-344 rats at 3, 7, 14 and 28 days after stereotaxic injection of ibotenate into the right NBM, and in sham-operated animals at 3 and 14 days later. For both ages the peak effect of unilateral NBM ablation occurred 3 days later: in young rats, rCMRglc was significantly reduced (compared to the contralateral side) in all 24 anterior cortical areas examined (mean decline 20%), whereas in aged animals, only 9 of 24 areas showed a significant decline in glucose utilization, and the magnitude of rCMRglc reduction (9%) was smaller. Near complete recovery of rCMRglc occurred by 7 days in young and old rats. We conclude that the basalocortical cholinergic projection plays a smaller role in neocortical function of aged rats, possibly because its tonic activity is reduced. Both young and aged rats undergo cortical metabolic normalization after unilateral NBM ablation; hence the NBM-lesioned aged rat is not a better model of the progressive decline in rCMRglc that occurs in Alzheimer's disease.

Interregional correlations of resting cerebral glucose metabolism in old and young women

A correlational analysis of normalized (regional to whole-brain) regional cerebral metabolic rates for glucose obtained in the 'resting' state (eyes covered, ears plugged) using [18F]fluorodeoxyglucose, demonstrated differences between old and young women in patterns of functional associations. Fifteen healthy young (age less than 40 years) and 17 healthy old women (age greater than 64 years) were scanned with a Scanditronix PC1024-7B tomograph. The brain was divided into 65 regions of interest. The old women had fewer and less positive correlations between pairs of metabolic ratios in the frontal and parietal cortices. The results suggest an age-related reduction in frontal and parietal functional interactions in the 'resting' state that is consistent with a prior correlation analysis using a low resolution ECAT II scanner on young and old men. Reduced functional interactions may reflect age-related cognitive changes.

Positron emission tomography study of the human hypothalamus during normal ageing and in ischemic and degenerative disorders

Regional blood flow and oxygen metabolism were determined by positron emission tomography, using the steady state technique with 15O, in the hypothalamus and in the whole brain of fifty two normal persons and patients suffering from cerebral ischemia and degenerative dementia. During normal ageing regional blood flow and oxygen consumption appeared to increase slightly in the hypothalamus and to decrease in the whole brain in 24 persons. In the young age group the hypothalamus was more protected against ischemia than in the elderly group. In the aged group with cerebral ischemia and degenerative dementia regional blood flow and oxygen consumption were decreased in the hypothalamus to the same extent as in the whole brain.

Factor analysis of regional cerebral glucose metabolic rates in healthy men

Cerebral glucose utilization measured with fluorine-18-fluoro-2-deoxy-D-glucose is characterized by considerable variability both among different persons and for the same person examined on different occasions. The goal of this study was to explore whether some regions of the brain were more variable than others with respect to glucose utilization and whether there was a pattern in their covariance. The global and regional cerebral utilization of glucose was measured in 12 healthy young volunteers on 3 or 4 occasions. In all, 24 regions were examined. The interrelation of the glucose utilization rates of the brain regions was investigated by factor analysis of the metabolic rates. Some 70% of the total variance was attributable to only 1 factor, while 80% of the total variance could be attributed to 2 factors. Regions making up the first factor were the frontal and temporal cortex, cingulate gyrus, caudate nucleus, thalamus and putamen. These regions are functionally related to the limbic system. Regions of the second factor were the parietal cortex, occipital cortex and cerebellum, regions more clearly related to sensory and motor functions. The 2-factor pattern was highly reproducible, being found with different algorithms for factor extraction and rotation. Under resting conditions, the variance of cerebral metabolism seems to be primarily related to regions which are closely involved with the limbic system. Cortical regions involved primarily in motor and sensory functions have less influence on the variance.

Vibration-induced regional cerebral blood flow responses in normal aging

Task-induced changes in regional CBF (rCBF) can be measured with positron emission tomography (PET) and provide a powerful tool to map brain function. Many studies using these techniques have investigated responses in healthy young subjects. Since many pathological conditions occur more commonly in older subjects, it is necessary to compare blood flow responses in these patients with appropriately age-matched controls. Furthermore, the effects of normal aging on such blood flow responses remain unknown. For both reasons, we designed this study to determine whether vibration-induced CBF responses change with advancing age in normals. CBF was measured with PET and bolus-administered H2(15)O in 26 subjects from 20 to 72 years old (mean = 39; SD = 19). Regional responses were identified by subtraction-image analysis. Left and right hand vibration produced consistent responses in contralateral primary sensorimotor area (PSA) and supplementary motor area (SMA). Response magnitudes were compared to age by linear regression. There were no substantial relationships between age and responses to vibration for PSA or SMA (PSA r = -0.28, p = 0.054; SMA r = -0.33, p = 0.13). Power analysis demonstrates a high degree of confidence (99.7% for PSA and 87% for SMA) for detecting at least a moderate correlation (r = 0.6) between response magnitude and age. We conclude that the rCBF responses to vibrotactile hand stimulation do not change with normal aging.

Verbal fluency and positron emission tomographic mapping of regional cerebral glucose metabolism

Impairment in verbal fluency (VF) has been a consistently reported clinical feature of focal cerebral deficits in frontal and temporal regions. More recent behavioral activation studies with healthy control subjects using positron emission tomography (PET), however, have noted a negative correlation between performance on verbal fluency tasks and regional cortical activity. To see if this negative relationship extends to steady-state non-activation PET measures, thirty-three healthy adults were given a VF task within a day of their 18F-2-fluoro-2-deoxy-D-glucose PET scan. VF was found to correlate positively with left temporal cortical region metabolic activity but to correlate negatively with right and left frontal activity. VF was not correlated significantly with right temporal cortical metabolic activity. Some previous studies with normals using behavioral activation paradigms and PET have reported negative correlations between metabolic activity and cognitive performance similar to that reported here. An explanation for the disparate relationships that were observed between frontal and temporal brain areas and VF might be found in the mediation of different task demands by these separate locations, i.e., task planning and/or initiation by frontal regions and verbal memory by the left temporal area.

Gender differences in correlations of cerebral glucose metabolic rates in young normal adults

Correlational analysis of normalized regional cerebral metabolic data obtained by positron emission tomography, in healthy subjects in the 'resting' state (eyes covered, ears plugged) using [18F]2-fluoro-2-deoxy-D-glucose, demonstrated gender differences in patterns of functional associations. Fifteen women and 18 men (less than 40 yr) were scanned with a Scanditronix PC1024-7B tomograph. The brain was divided into 65 regions of interest (ROIs). There were no differences between men and women in global or regional metabolic rates, or in metabolic right-left asymmetries. Although the total number of significant correlations did not differ between men and women, patterns differed: female correlations rF were most positive than male correlations rM more often than rM greater than rF; and most rF greater than rM cases involved left frontal and sensorimotor ROIs, whereas most rM greater than rF cases involved right sensorimotor and occipital ROIs. The findings demonstrate gender differences in the pattern of functional neocortical interactions at the 'resting' state.

The influence of biological and technical factors on the variability of global and regional brain metabolism of 2-[18F]fluoro-2-deoxy-D-glucose

This study investigated the influence of biological and technical factors on variations of global and regional cerebral metabolic rate of glucose (CMRglc) measured with 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG). Twelve male volunteers (22-40 years) were investigated on three or four occasions for a total of 42 studies. We calculated the variance/covariance of the following parameters: CMRglc, six parameters of the blood clearance of [18F]FDG, hour of injection, peak time of blood radioactivity, and six components of the operational equation (nonradioactive blood glucose concentration, brain radioactivity, two integrals, numerator, and denominator). There was correlation among these six components, except for nonradioactive blood glucose. However, the correlation between the CMRglc and the individual components of the operational equation was poor. The inter- and intrapersonal CMRglc coefficients of variations were 13.8 and 7.1%, respectively. In contrast, coefficients of variations of the numerator and denominator of the operational equation were 34.6 and 32.6%, respectively, and were always in the same direction. No correlation was found between CMRglc and the technical factors in the numerator and denominator of the operational equation. Factor analysis disclosed that a single factor was responsible for 70% of the variance. This factor included caudate, putamen, thalamus, frontal cortex, temporal cortex, and cingulate gyrus. These structures are involved with multiple complex functions, from autonomic motor control to behavior and emotions. The intrinsic metabolic variability of these structures, along with the basal metabolic processes that are continuously going on in the brain, may be the best explanation for the variance encountered in our investigation.

Glucose metabolism in psychiatric disorders: how can we facilitate comparisons among studies?

Positron emission tomography (PET) offers a possibility to study brain function and its relationship to psychiatric disorders. Clinical studies have demonstrated that several psychiatric diseases are coupled with changes in brain glucose metabolism. Schizophrenia seems to involve a lower metabolism in wide areas of the brain--both cortical and subcortical structures. Depression probably involves dysfunction of the metabolism in dorsolateral prefrontal cortex. Obsessive compulsive disorder, panic disorder, anorexia nervosa and the experience of anxiety may involve increased metabolic rates. The results from the different studies do not allow quantitative comparisons or detailed analyses because of large differences in experimental and clinical methodology. The term Good Clinical PET Practice (GCPP) is suggested to encourage standardization in clinical investigations. GCPP includes standardization of both experimental factors (lumped constant, arterialization, purity of tracer, regions of interest, relative rates) and clinical factors (state of the subject, wakefulness, anxiety, gender, course of the disease) in PET performance.

Oral health of patients with Alzheimer's disease

Generally healthy, unmedicated patients with Alzheimer's disease have few but significant changes in their oral health. Study results reinforce preventive oral hygiene for these patients.

Physostigmine in Alzheimer's disease: effects on cognitive functioning, cerebral glucose metabolism analyzed by positron emission tomography and cerebral blood flow analyzed by single photon emission tomography

The effect of acute, intravenous administration of physostigmine on measures of brain activity and cognitive functioning were investigated in 14 patients with Alzheimer's disease. Regional cerebral glucose metabolism was assessed using (18F)-fluoro-2-deoxy-D-glucose and positron emission tomography, and cerebral blood flow was assessed using 123I-iodoamphetamine single photon emission tomography. Although physostigmine enhanced cerebral blood flow in most patients, only one patient showed significant clinical improvement. This patient, however, also showed a very pronounced improvement in cerebral glucose metabolism. It is concluded that these preliminary findings hold considerable promise for our appreciation of the pathophysiology of dementing illness as well as our understanding of centrally acting compounds of interest in Alzheimer's disease.

Neuronal bioenergetic defects, excitotoxicity and Alzheimer's disease: "use it and lose it"

Although excitotoxicity has been implicated in the pathogenesis of Alzheimer's disease, it is not likely to be the cause of this disorder. On the other hand, in the presence of the well-documented neuronal bioenergetic defects in Alzheimer's disease, normal concentrations of glutamate may become lethal, and excitotoxicity may become the final common pathway to cell death.

Decreases in regional cerebral blood flow with normal aging

Positron emission tomographic (PET) images of regional cerebral blood flow (rCBF) from 30 normal, resting volunteers aged 30 to 85 years were analysed to identify areas where rCBF fell with age. Images were anatomically normalised, and a pixel-by-pixel linear regression was performed to remove differences in global CBF between subjects. Pixels at which rCBF then showed a significant (p less than 0.01) negative correlation with age were identified. They were displayed as a statistical parametric map (SPM) of correlations. We demonstrate an age-related decrease in adjusted rCBF in the cingulate, parahippocampal, superior temporal, medial frontal, and posterior parietal cortices bilaterally, and in the left insular and left posterior prefrontal cortices (omnibus significance, chi 2 = 2,291, p less than 0.0001, df = 1). Decreases in rCBF suggest a regionally specific loss of cerebral function with age. The affected areas were all limbic, or association, cortices. Therefore, these decreases may constitute the cerebral substrate of the cognitive changes that occur during normal aging.

Global and regional cerebral metabolic rate of 2-[18F]fluoro-2-deoxy-D-glucose in the presence of ofloxacin, a gamma-aminobutyric acid a receptor antagonist

We investigated the effects of ofloxacin, a new antibacterial quinolone gamma-aminobutyric acid A receptor antagonist, on the global and regional cerebral metabolic rates of glucose (cMRgl). Twelve healthy normal male volunteers (mean age, 26.7 years) were studied in a double-blind, placebo-controlled protocol of 11 days' duration. Results of a total of 42 positron emission tomography studies were obtained for these subjects: 12 base line, 18 during placebo, and 12 during ofloxacin administration. The conditions under which repeat positron emission tomography studies of the same subject were performed were reproduced as closely as possible. cMRgl was measured in 24 brain regions. The global cMRgl for base line, placebo, and ofloxacin were 8.82 +/- 1.17, 8.24 +/- 1.17, and 8.79 +/- 1.18 mg/min/100 g, respectively (mean +/- 1 standard deviation). The mean global differences between base line and placebo and between ofloxacin and placebo were 5.1 and 6.6%, respectively. Analysis of variance of both the global and the regional cMRgl showed no statistical difference between base-line, placebo, and ofloxacin studies. Variations in cMRgl found in this study were not related to the presence of ofloxacin. Results of our study demonstrate that ofloxacin does not increase or decrease cMRgl beyond the limits of variability of the study.

Local cerebral glucose utilization in the brain of old, learning impaired rats

The local cerebral glucose utilization (LCGU) was measured in 63 different cortical areas and nuclei of the telencephalon, diencephalon and rhombencephalon of young adult (3 to 4-month-old) rats and of 27-month-old Wistar rats, in which learning impairments had been proven by a water maze test. The LCGU was determined by [14C]2-deoxyglucose autoradiography. In the old rats the mean LCGU of all brain regions was significantly reduced by about 10% compared with the young control group; the mean LCGU was 74.2 mumol glucose/(100 g x min) in the young and 66.7 in the old rats. Different degrees of LCGU decrease were found in the different regions. Most of the brain regions with significantly reduced LCGU values in the aged, learning impaired rats were associated with auditory and visual functions, the dopaminergic system, and structures known to be involved in learning and memory processes. Therefore, the regional pattern of LCGU reduction found in the aged, learning impaired rats did not resemble any known pattern found after lesions of a single transmitter system or systemic administration of transmitter agonists or antagonists.

Quantitative comparison of measurements of cerebral glucose metabolic rate made with two positron cameras

The rapid progress in PET technology has created the dilemma of how to compare data from old and new tomographs. We examined cerebral metabolic data from two scanners, with different spatial resolutions and methods of attenuation correction, to see if metabolic values from the lower-resolution tomograph (ECAT II) could be adjusted to make them comparable to data from the higher-resolution scanner (Scanditronix PC1024-7B). Nine subjects were scanned on both tomographs after a single injection of [18F]2-fluoro-2-deoxy-D-glucose. Regional and lobar gray matter metabolic rates for glucose were obtained from comparable images from each scanner. Ratios of lobar to global gray matter metabolism also were calculated. Regression coefficients and percent differences were computed to compare ECAT II and PC1024 data. Two-thirds of the region pairs showed significant regressions, although percent differences were quite variable, with measures of glucose utilization ranging from 30 to 120% higher on the PC1024 compared to those from the ECAT II. Comparisons of lobar glucose rates between the two machines were less variable (50 to 80%), and ratios differed by only +/- 5% (except for the temporal ratios). Since there was no simple and consistent relationship between regional metabolic rates on the two tomographs, an overall adjustment of regional ECAT values for comparison to PC1024 values would be impossible. A region-by-region adjustment would be necessary. Lobar ratios are sufficiently similar that direct comparisons might be possible.

Functional interactions in the brain: use of correlations between regional metabolic rates

Correlation coefficients between pairs of regional metabolic rates have been used to study patterns of functional associations among brain regions in humans and animals. An overview is provided concerning the additional information about brain functioning this type of analysis yields. A computer simulation model is presented for the purpose of giving a partial validation for correlational analysis. The model generates a set of simulated metabolic data upon which correlational analysis is performed. Because the underlying pattern of functional couplings in the model is known, these simulations demonstrate that the correlation coefficient between normalized metabolic rates is proportional to the strength of the functional coupling constant and that correlational analysis yields information on regional involvement in neural systems not evident in the pattern of absolute metabolic values.

Anxiety levels in dreams: relation to localized cerebral glucose metabolic rate

Ten normal male subjects were injected with D-[18F]deoxyglucose during REM sleep, and 32-45 min later they were aroused and reported their dreams as well as free associations to these dreams. Nonparametric correlations between the anxiety scores derived from the typescripts of these verbal reports by the Gottschalk-Gleser content analysis method and localized cerebral glucose metabolic rates obtained from PET scans revealed significant positive correlations in lateral parietal and medial frontal cortex and negative correlations in adjacent white matter.

Divided attention and metabolic brain dysfunction in mild dementia of the Alzheimer's type

The relationship between reaction time (RT) measures under single-task and dual-task conditions and resting levels of brain metabolism, as measured by positron emission tomography (PET), was examined in patients with mild dementia of the Alzheimer type (DAT) and age- and educationally-matched controls. Slowing of RT in dual-task but not single-task conditions correlated with reductions in brain metabolism in right premotor and right parietal association areas only for the mild DAT patients. The results suggest a relation between divided attention deficits and metabolic dysfunction of right frontal and parietal lobes in mild DAT patients.

Effect of gender on glucose utilization rates in healthy humans: a positron emission tomography study

Positron emission tomography (PET) was used with 18fluorodeoxyglucose to see if gender differences in resting cerebral glucose utilization could be detected. Thirty-two healthy subjects (15 women and 17 men; age range: 21-38 yr) were examined using a high-resolution PET scanner to determine the regional cerebral metabolic rate for glucose (CMRglc) in 65 gray matter regions of interest. Whole brain CMRglc did not differ significantly between the two genders, nor did any of the regional CMRglc values. Only 1 of 65 ratios of regional-to-whole brain CMRglc differed significantly between men and women, which is consistent with chance. These results indicate that there are no differences in resting regional cerebral glucose utilization between young men and women.

Obsessive-compulsive disorder: a clinical, neuropsychological and positron emission tomography study

The authors compared 16 nondepressed obsessive-compulsive patients (OCS) with 8 normal controls (NC) of similar age for resting-state regional cerebral glucose metabolic rates (rCMRglu) using positron emission tomography with the fluorodeoxyglucose method. OCS were rated for clinical data, and a neuropsychological battery was administered to 14 patients on the day of the scan. Absolute rCMRglu for whole cortex, and normalized prefrontal lateral cortex metabolic rates, were both significantly lower in OCS than in NC. No significant difference between treated (n = 10) and drug-free (n = 6) OCS was found for those variables. OCS were significantly impaired in the neuropsychological tasks assessing memory and attention. The rCMRglu for prefrontal lateral cortex were negatively correlated to Stroop-test subscores. This "frontal-oriented" task assessed the ability of OCS to inhibit immediate but inappropriate responses. These results suggest, in OCS, a modification of the general activating systems of cortical function and a relationship between the lateral prefrontal rCMRglu decrease and a selective attention deficit.

Simulating functional interactions in the brain: a model for examining correlations between regional cerebral metabolic rates

A computer simulation model was developed to investigate the use of interregional correlations of cerebral metabolic rates to analyze functional interactions in the brain. The model generates simulated metabolic data for individual brain regions in a specified number of subjects, where there are defined functional couplings amongst the regions. Random numbers provide the variability seen in measured metabolic data. Correlational analysis is performed on these simulated data sets. The parameters of the model can be chosen so that simulated and actual metabolic data are very similar. The model demonstrates that the change in the correlation coefficient between normalized metabolic data in two brain regions is related to the change in the strength of the functional association between the two regions. The model also is used to explore the relations between patterns of correlations and the underlying sets of functional couplings. The results indicate that correlational analysis provides more information about regional involvement in neural systems than does region-by-region comparisons of absolute metabolic rates.

Selective hypometabolism in the inferior frontal lobe in depressed patients with Parkinson's disease

Depression is a frequent finding in patients with Parkinson's disease (PD). Regional cerebral glucose metabolism was measured in depressed and nondepressed patients with PD and in age-comparable normal control subjects using 2-[18F]-fluoro-2-deoxy-D-glucose and positron emission tomography (PET). Relative metabolic activity in the caudate and orbital-inferior region of the frontal lobe was significantly lower in the depressed patients with PD as compared to both nondepressed patients and control subjects. There was a significant inverse correlation between relative glucose metabolism in the orbital-inferior area of the frontal lobe and depression scores. This study suggests that depression in PD is associated with dysfunction in the caudate and orbital-inferior area of the frontal lobe. This metabolic pattern is unlike that seen in patients with PD who have other behavioral deficits such as dementia, and suggests that disruption of basal ganglia circuits involving the inferior region of the frontal lobe may affect the regulation of mood.

Anxiety and cerebral cortical metabolism in normal persons

The State-Trait Anxiety Inventory (STAI) was administered to 43 normal volunteers immediately before and after a positron emission tomography (PET) procedure with [18F]-2-fluoro-2-deoxy-D-glucose (18F-FDG). High trait-anxious individuals had significantly higher state (situational) anxiety associated with the PET scan procedure than did low trait-anxious persons. State anxiety decreased significantly for all respondents following the PET scan procedure. No significant relationships between global or regional cortical metabolic rates and state anxiety were observed. The direct cortical metabolic effects of heightened anxiety in the scan setting, should they exist, are likely obscured in the normal variance of the 18F-FDG method.

Reproducibility of cerebral glucose utilization measured by PET and the [18F]-2-fluoro-2-deoxy-d-glucose method in resting, healthy human subjects

The stability of cerebral glucose utilization was examined in nine right-handed, healthy men (age, 24.88 +/- 2.93 years) using positron emission tomography (PET) and the [18F]-fluorodeoxglucose (FDG) method. Each study was run twice at intervals of 1-12 weeks with the subject at rest. The average cerebral metabolic rate for glucose (CMRGlu) was 5.40 +/- 0.71 mg/100 g per min (coefficient of variance, 13.08). The average intraindividual variation of CMRGlu was 7.91% +/- 15.46% (P = 0.13). Metabolic indices (MI: regional/mean cortical CMRGlu) were used to determine the regional cerebral metabolic distribution. The interindividual (coefficient of variance, 7.13) and intraindividual variabilities (average variation, -0.12% +/- 8.76%) of MI were smaller than those of metabolic rates. No reproducible significant asymmetry was observed. The FDG method used with subjects at rest thus yields low intraindividual variability of both cerebral glucose consumption and regional metabolic distribution, even at an interval of several weeks. Cerebral glucose utilization measured under such conditions may act as a reliable reference for determination of the influences of physiological (activation), pharmacological or pathological processes on cerebral glucose metabolism.

A multidimensional approach in testing nootropic drug effects (Cerebrolysin®)

In an attempt to improve indicators of validity for the therapeutic efficacy of nootropics, the effects of Cerebrolysin(R) were compared across three different dimensions of variables in a randomized placebo-controlled double-blind study. A group of 27 geriatric patients suffering from an organic brain syndrome with moderate cognitive impairment of a vascular or/and degenerative nature received a series of ten Cerebrolysin + multivitamin infusions. They were compared to a second group with 14 clinically comparable patients, who received multivitamin infusions alone. Pre-posttreatment differences from (1) clinical scales (SCAG, Plutchik Geriatric Rating Scale and a self-evaluation scale); (2) psychometric test performance (trail-making and maze subtests from the Nürnberg Age Inventory); and (3) event-related brain activity (contingent negative variation (CNV) amplitude) were in favor of the Cerebrolysin-treated group. A high degree of association as well as high classification rates (95% joint correct classification) underlined their clinical significance. It was concluded that the multidimensional measurement approach could increase the clinical validity of nootropic drug effects.

Regional cerebral glucose metabolism is normal in young adults with Down syndrome

Regional CMRglc (rCMRglc) values were measured with [18F]2-fluoro-2-deoxy-D-glucose (18FDG) and positron emission tomography (PET), using a Scanditronix PC-1024-7B scanner, in 14 healthy, noninstitutionalized subjects with trisomy 21 (Down syndrome; DS) (mean age 30.0 years, range 25-38 years) and in 13 sex-matched, healthy volunteers (mean age 29.5 years, range 22-38 years). In the DS group, mean mental age on the Peabody Picture Vocabulary Test was 7.8 years and dementia was not present. Resting rCMRglc was determined with eyes covered and ears occluded in a quiet, darkened room. Global gray CMRglc equaled 8.76 +/- 0.76 mg/100 g/min (mean +/- SD) in the DS group as compared with 8.74 +/- 1.19 mg/100 g/min in the control group (p greater than 0.05). Gray matter regional measurements also did not differ between groups. The ratio of rCMRglc to global CMRglc, calculated to reduce the variance associated with absolute rCMRglc, and right/left ratios did not show any consistent differences. These results show that healthy young DS adults do not have alterations in regional or global brain glucose metabolism, as measured with 18FDG and PET, prior to an age at which the neuropathological changes in Alzheimer disease are reported to occur.