1,721,004 research outputs found
Altered brain functional connectivity and impaired short-term memory in Alzheimer's disease
No full textTo examine functional interactions between prefrontal and medial temporal brain areas during face memory, blood flow was measured in patients with Alzheimer's disease and healthy controls using PET. We hypothesized that controls would show correlated activity between frontal and posterior brain areas, including the medial temporal cortex, whereas patients would not, although frontal activity per se might be spared or even increased compared with controls. We used a delayed match to sample paradigm with delays from 1 to 16 s. There was no change in recognition accuracy with increasing delay in controls, whereas patients showed impaired recognition over all delays that worsened as delay increased. Controls showed increased activity in the bilateral prefrontal and parietal cortex with increasing delay, whereas the patients had increased activity in the right prefrontal, anterior cingulate and left amygdala. Increased activity in the right prefrontal cortex was associated with better me..
Cerebral metabolic pattern in obsessive-compulsive disorder: altered intercorrelations between regional rates of glucose utilization
No full textCorrelations between normalized regional cerebral metabolic rates for glucose, determined by positron emission tomography with 18F-2-fluoro-2-deoxy-D-glucose, were used to investigate functional associations between pairs of brain regions in 18 adult patients with primary obsessive-compulsive disorder (OCD) of childhood-onset, as compared with 18 age- and sex-matched control subjects. The number of correlations that differed significantly between the two groups exceeded chance, although as many of these correlations were larger in the OCD group relative to controls as were smaller. The two regions that had the largest number of correlations that differed significantly between groups were a left hemisphere superior parietal region and the left hemisphere anterior medial temporal area (which includes principally the amygdala). Correlations involving the caudate nuclei did not differ between the two groups for the most part. Anterior limbic/paralimbic regions had correlations in the OCD group that were significantly larger with frontal areas than in controls, and correlations that were significantly smaller with posterior brain regions. This pattern was especially pronounced for the left hemisphere anterior medial temporal region. These results suggest that the correlation pattern in OCD is not characterized by an overall loss of functional integration but, rather, by functional reorganization
Heterogeneity of regional cerebral glucose metabolic patterns in neuropathologically confirmed Alzheimer's disease
No full textThe functional organization of human extrastriate cortex: a PET-rCBF study of selective attention to faces and locations
No full textThe functional dissociation of human extrastriate cortical processing streams for the perception of face identity and location was investigated in healthy men by measuring visual task-related changes in regional cerebral blood flow (rCBF) with positron emission tomography (PET) and H2(15)O. Separate scans were obtained while subjects performed face matching, location matching, or sensorimotor control tasks. The matching tasks used identical stimuli for some scans and stimuli of equivalent visual complexity for others. Face matching was associated with selective rCBF increases in the fusiform gyrus in occipital and occipitotemporal cortex bilaterally and in a right prefrontal area in the inferior frontal gyrus. Location matching was associated with selective rCBF increases in dorsal occipital, superior parietal, and intraparietal sulcus cortex bilaterally and in dorsal right premotor cortex. Decreases in rCBF, relative to the sensorimotor control task, were observed for both matching..
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
Attention-related modulation of activity in primary and secondary auditory cortex
No full textWe investigated the effects of auditory attention on brain activity using functional magnetic resonance imaging. Subjects listened to three word lists, three times each, and were instructed to count the number of times they heard a target word during two of these presentations. For the third, they listened to the words without counting. All subjects showed significant areas of activation in auditory cortex during the listening conditions compared to rest. There was significantly more activation and a larger area of activation, particularly in association cortex, in the left temporal lobe during counting of targets compared to the no-target conditions, with a similar trend in the right hemisphere. These results provide evidence of an attention-related enhancement of both activation magnitude and extent in auditory cortex
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
Reductions in parietal and temporal cerebral metabolic rates for glucose are not specific for Alzheimer's disease
No full textReduction in the regional cerebral metabolic rate for glucose (rCMRglc) in the parietal and temporal regions has been shown in Alzheimer's disease (AD). The specificity of these findings for this disease state is uncertain. We repeatedly measured rCMRglc with positron emission tomography and [18F]2-fluoro-2-deoxy-D-glucose in the resting state in a 68 year old man with slowly progressive dementia who, during life, was initially diagnosed as having dementia of the Alzheimer type, then Parkinson disease with dementia, but was found to have only Parkinson's disease at necropsy. Metabolic ratios (rCMRglc/mean grey CMRglc) were significantly (p < 0.05) reduced in parietal and temporal regions, as well as in the prefrontal and premotor areas. This pattern was similar in regional distribution and magnitude of the defect to that seen in patients with probable AD. These results suggest that reductions of glucose metabolism in association neocortex in AD are not specific to the disease process, but may be related to the dementia state
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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