1,720,981 research outputs found
Increasing required neural response to expose abnormal brain function in mild versus moderate or severe Alzheimer’s disease: PET study using parametric visual stimulation
No full textAbstract
OBJECTIVE:
The authors examined the interaction of Alzheimer's disease severity and visual stimulus complexity in relation to regional brain function.
METHOD:
Each subject had five positron emission tomography [15]H2O scans while wearing goggles containing a grid of red lights embedded into each lens. Regional cerebral blood flow (CBF) was measured at 0 Hz and while lights were flashed alternately into the two eyes at 1, 4, 7, and 14 Hz. Changes in regional CBF from the 0-Hz baseline were measured at each frequency in 19 healthy subjects (mean age = 65 years, SD = 11), 10 patients with mild Alzheimer's disease (mean age = 69, SD = 5; Mini-Mental State score > or = 20), and 11 patients with moderate to severe Alzheimer's disease (mean age = 73, SD = 12; Mini-Mental State score < or = 19).
RESULTS:
As pattern-flash frequency increased, CBF responses in the comparison group included biphasic rising then falling in the striate cortex, linear increase in visual association areas, linear decrease in many anterior areas, and a peak at 1 Hz in V5/MT. Despite equivalent resting CBF and CBF responses to low frequencies among all groups, the groups with Alzheimer's disease had significantly smaller CBF responses than the comparison group at the frequency producing the largest response in the comparison group in many brain regions. Also, patients with moderate/severe dementia had smaller responses at frequencies producing intermediate responses in comparison subjects.
CONCLUSIONS:
Functional failure was demonstrated in patients with mild dementia when large neural responses were required and in patients with moderate/severe dementia when large and intermediate responses were required
Abnormal brain glucose metabolism in the delusional misidentification syndromes: a positron emission tomography study in Alzheimer disease
No full textBrain lesions have been reported with increasing frequency in the delusional misidentification syndromes (DMS). This is the first controlled study to describe DMS regional cerebral metabolic rates of glucose (rCMRglc). We compared rCMRglc (using positron emission tomography) and neuropsychological data in 9 patients with DMS and Alzheimer dementia (AD), 15 AD patients without DMS, and 17 healthy controls. The DMS group differed from the AD group without DMS in having significant hypometabolism in paralimbic (orbitofrontal and cingulate areas bilaterally) and left medial temporal areas, and significant bilateral normalized hypermetabolism in sensory association cortices (superior temporal and inferior parietal) without right left asymmetry. Compared to healthy controls, both AD groups had significant dorso lateral frontal hypometabolism bilaterally. No specific DMS neuropsychological profile was identified. Dysfunctional connections among multimodal association areas, paralimbic structures, and dorsolateral frontal cortex are proposed as the predisposing neural deficit underlying DMS, causing cognitive-perceptual-affective dissonance, which under specific conditions results in "positive" delusion formation
Effect of task difficulty on cerebral blood flow during perceptual matching of faces
No full textTo aid our understanding of age-related changes in brain activation during visuoperceptual processing, we designed an experiment to test the effect of task difficulty on regional cerebral blood flow (rCBF) as measured by positron emission tomography (PET). We report here the results from 10 young subjects engaged in match-to-sample tasks of progressively degraded faces. The tasks consisted of a control task, a face matching task with no stimulus degradation, and five levels of degradation: 20%, 40%, 50%, 60%, and 70%. Both performance accuracy and reaction times deteriorated significantly with increasing face degradation. There was a significant increase of rCBF in bilateral fusiform gyri during all face-matching conditions compared to the control task, and bilateral prefrontal activation during the 70% degradation condition. Linear regression analyses revealed a significant increase of rCBF in the right prefrontal cortex, and linear decreases of rCBF in the striate and fusiform cortex as face degradation increased. Performance on the 70% task was correlated positively with rCBF in right prefrontal and bilateral fusiform gyri, and negatively with left prefrontal and striate rCBF. These results show that the right prefrontal, striate, and ventral extrastriate cortex are the principal brain regions that modulate their activity as this visual discrimination task becomes more difficult. The right prefrontal increase probably represents an increasing demand on working memory or attention, whereas decreased rCBF in the striate cortex may be due to changes in the characteristics of the stimuli, or to suppression of low-level processing by one of a number of mechanisms. This experiment has implications both for the design of neuroimaging experiments, and for interpreting differences in rCBF activation between groups
ASSOCIATION BETWEEN BRAIN FUNCTIONAL FAILURE AND DEMENTIA SEVERITY IN ALZHEIMER'S DISEASE: RESTING VERSUS STIMULATION PET STUDY
No full textAbstract
OBJECTIVE:
This study tested the hypothesis that regional cerebral glucose metabolism during neuronal activation is a more sensitive index of neuronal dysfunction and clinical severity in Alzheimer's disease than is glucose metabolism at rest.
METHOD:
The subjects were 15 Alzheimer's disease patients with a wide range of Mattis Dementia Rating Scale scores (23-128). By using positron emission tomography, absolute glucose metabolism was measured in the parietal, occipital (visual areas), and temporal (auditory areas) cortical regions during rest (eyes/ears covered) and audiovisual stimulation.
RESULTS:
In the parietal cortex, glucose metabolism correlated with dementia severity in both conditions. In contrast, in the relatively preserved visual and auditory cortical regions, glucose metabolism predicted dementia severity during stimulation but not at rest.
CONCLUSIONS:
These findings suggest that regional cerebral glucose metabolism during stimulation is a more sensitive index of the functional/metabolic failure of neuronal systems than is metabolism at rest
Association of premorbid intellectual function with cerebral metabolism in Alzheimer's disease: implications for the cognitive reserve hypothesis
No full textObjective: Clinical heterogeneity in Alzheimer's disease has been widely observed. One factor that may influence the expression of dementia in Alzheimer's disease is premorbid intellectual ability. It has been hypothesized that premorbid ability, as measured by educational experience, reflects a cognitive reserve that can affect the clinical expression of Alzheimer's disease. The authors investigated the relation between estimates of premorbid intellectual function and cerebral glucose metabolism in patients with Alzheimer's disease to test the effect of differing levels of premorbid ability on neurophysiological dysfunction. Method: In a resting state with eyes closed and ears occluded, 46 patients with Alzheimer's disease were evaluated with positron emission tomography and [ 18F]-2- fluoro-2-deoxy-D-glucose to determine cerebral metabolism. Premorbid intellectual ability was assessed by a demographics-based IQ estimate and performance on a measure of word-reading ability. Results: After the authors controlled for demographic characteristics and dementia severity, both estimates of premorbid intellectual ability were inversely correlated with cerebral metabolism in the prefrontal, premotor, and left superior parietal association regions. In addition, the performance-based estimate (i.e., reading ability) was inversely correlated with metabolism in the anterior cingulate, paracentral, right orbitofrontal, anti left thalamic regions, after demographic and clinical variables were controlled for. Conclusions: The results suggest that higher levels of premorbid ability are associated with greater pathophysiological effects of Alzheimer's disease among patients of similar dementia severity levels. These findings provide support for a cognitive reserve that can alter the clinical expression of dementia and influence the neurophysiological heterogeneity observed in Alzheimer's disease
AGE-RELATED REDUCTIONS IN HUMAN RECOGNITION MEMORY DUE TO IMPAIRED ENCODING
No full textThe participation of the medial temporal cortex and other cerebral structures in the memory impairment that accompanies aging was examined by means of positron emission tomography. Cerebral blood flow (rCBF) was measured during encoding and recognition of faces. Young people showed increased rCBF in the right hippocampus and the left prefrontal and temporal cortices during encoding and in the right prefrontal and parietal cortex during recognition. Old people showed no significant activation in areas activated during encoding in young people but did show right prefrontal activation during recognition. Age-related impairments of memory may be due to a failure to encode the stimuli adequately, which is reflected in the lack of cortical and hippocampal activation during encoding
Quantitative medial temporal lobe volumes in frontotemporal dementia, Alzheimer's disease, and healthy aging
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