Biomedical subjects

C L Grady

Publications and source records attributed to C L Grady.

97 records · Page 6Linked to original sources

PubMed1979

Effects of increased testosterone secretion on the behavior of adult male rhesus living in a social group.

Selected members of an all-male social group of rhesus monkeys were treated with twice-weekly injections of human chorionic gonadotropin (HCG) to determine the effects of the consequently increased androgen secretion on social behavior. Radioimmunoassay of blood samples confirmed significant increases in serum testosterone levels in each of 4 subject, but only 3 of these showed significant behavioral changes. The basic social structure of the group, including the dominance hierarchy, was not disrupted by the treatment with HCG. Rather, the behavioral changes which did not occur appeared to be intensifications of previously existing social relationship.

Aggression↗

PubMedDate not supplied

Nature of mental retardation and dementia in Down syndrome: study with PET, CT, and neuropsychology.

Recent evidence suggests that Alzheimer's disease is an etiologically heterogeneous disorder. A human model of Alzheimer's disease exists that avoids such problems of etiologic heterogeneity. Down syndrome (DS), trisomy 21, is a genetic disorder in which an extra portion of chromosome 21 leads to mental retardation, short stature, and phenotypic abnormalities. Prior investigations by others have shown that DS subjects over 40 years of age demonstrate neuropathologic and neurochemical defects postmortem that are virtually indistinguishable from those found in brains of Alzheimer's disease patients and a universal cognitive deterioration more severe in demented than nondemented older DS subjects. In our study, these nondemented older DS subjects show a distinctive pattern of age-related deficits, while a more global pattern is seen in demented older DS subjects. Dementia occurs in 40% of older DS subjects. We find that in older demented DS subjects positron emission tomography (PET) shows identical patterns of abnormal glucose metabolism as those described previously in Alzheimer's disease patients, selectively involving the phylogenetically newer association areas of parietal and temporal neocortices but sparing primary sensory and motor regions. Further, we find in older demented DS patients quantitative computer-assisted tomography (CT) indicates accelerated neuronal loss and brain atrophy, similar to that previously shown in Alzheimer's disease patients. As a potential use of the DS model, we observed a case of DS with dementia but without mental retardation. This case suggests that expression of dementia in DS may involve genes on chromosome 21 other than in the "obligatory" distal segment of the q arm. Alternatively, differential expression of genes on the q arm of chromosome 21 might cause dementia without phenotypic features and mental retardation.

Dementia↗

PubMedDate not supplied

Activation of cerebral blood flow during a visuoperceptual task in patients with Alzheimer-type dementia.

Changes in regional cerebral blood flow (rCBF) associated with a face-matching task were examined using positron emission tomography (PET) and H2(15)O in 7 patients with mild-moderate dementia of the Alzheimer type (DAT) and in 8 healthy age-matched controls. rCBF was normalized to whole brain flow and pixel-by-pixel difference images were computed by contrasting flow during a control task to flow during face matching. Both patients and controls showed bilateral rCBF increases in occipitotemporal extrastriate cortex during face matching. The magnitude of these increases was not significantly different between the groups. In addition, the patients showed greater rCBF activation in regions of occipital and frontal cortex. These results show that early in the course of DAT, patients utilize extrastriate cortex to perform a visuoperceptual task, as do control subjects but also show rCBF increases in additional cortical areas. Activation of these additional areas of cortex in the patients may reflect an increased attentional load during face matching due to their reduced cognitive capacity.

Aged↗

PubMedDate not supplied

Brain imaging and age-related changes in cognition.

Although there is currently some debate as to the degree of structural changes in the brain that occur with age, there is little doubt that such changes occur. There also are physiological changes in many areas that could have implications for cognitive function in the elderly. One way to study the impact of these age-related changes in the brain on cognition is to use neuroimaging techniques to examine brain activity during the performance of various tasks, and determine how this activity differs between young and older individuals. This approach has been used to study functions such as memory, perception, and attention, and it has generally been found that older individuals utilize different areas of the brain than do young subjects when carrying out the same cognitive task. This has led some researchers to suggest that older persons utilize different functional brain networks, perhaps to compensate for reductions of efficiency in some brain areas. The areas of the brain most often found to be more active during cognitive tasks in the elderly are the frontal lobes. Studies that have directly examined the functional networks utilized during cognition have found that older people do indeed have different functional interactions involving the frontal lobes, and therefore, utilize different functional networks. In some cases this differential activity has been accompanied by cognitive performance in the older participants that is equivalent to that seen in the young, suggesting that greater reliance on this brain region is related in some way to the maintained ability of the older individuals to perform the task. However, data collected to date on this issue are still limited, so although the evidence is intriguing, the definitive interpretation of these findings must await further experiments.

Aging↗

PubMedDate not supplied

PET reveals occipitotemporal pathway activation during elementary form perception in humans.

To define brain regions involved in feature extraction or elementary form perception, regional cerebral blood flow (rCBF) was measured using positron emission tomography (PET) in subjects viewing two classes of achromatic textures. Textures composed of local features (e.g. extended contours and rectangular blocks) produced activation or increased rCBF along the occipitotemporal pathway relative to textures with the same mean luminance, contrast, and spatial-frequency content but lacking organized form elements or local features. Significant activation was observed in striate, extrastriate, lingual, and fusiform cortices as well as the hippocampus and brain stem. On a scan-by-scan basis, increases in rCBF shifted from the occipitotemporal visual cortices to medial temporal (hippocampus) and frontal lobes with increased exposure to only those textures containing local features. These results suggest that local feature extraction occurs throughout the occipitotemporal (ventral) pathway during extended exposure to visually salient stimuli, and may indicate the presence of similar receptive-field mechanisms in both occipital and temporal visual areas of the human brain.

Adult↗

PubMedDate not supplied

Changes in limbic and prefrontal functional interactions in a working memory task for faces.

Regional cerebral blood flow, measured with positron emission tomography, was used to identify brain regions that play a special role(s) in a working memory task for faces. Perceptual matching (no retention interval), short-delay (average = 3.5 s retention interval), intermediate-delay (average = 12.5 s), and long-delay (21 s) tasks were considered. From the idea that brain function is the result of neural interactions, the data were analysed using anatomically based, covariance structural equation modeling. In perceptual matching, the dominant functional interactions were observed among the ventral cortical areas, from extrastriate regions, to the anterior temporal, and into the inferior prefrontal cortex. These interactions decreased with longer delay intervals. In the short-delay functional model, interactions along this ventral stream in the right hemisphere appeared to be rerouted through limbic areas with strong interactions among the hippocampal region, the anterior and posterior cingulate, and the inferior prefrontal cortices. For the intermediate-delay model, the hippocampocingulate interactions continued, but showed a shift to more left hemisphere involvement. In the long-delay network, interactions within the right limbic circuit were reduced in favor of strong bilateral inferior prefrontal and frontocingulate interactions. Effects from the prefrontal cortex, especially from the left hemisphere, to temporal and occipito-temporal cortices were particularly strong in the long-delay model, suggesting recruitment of some of the same circuits primarily involved in face perception. The strong corticolimbic interactions at short and intermediate delays may represent maintenance of an iconic representation of the face during the retention interval. However, at longer delays, where image was more difficult to maintain, a frontocingulate-occipital network was used that could represent an expanded encoding strategy resulting in a more resilient memory.

Adult↗

PubMedDate not supplied

Pattern of cerebral metabolic interactions in a subject with isolated amnesia at risk for Alzheimer's disease: a longitudinal evaluation.

A pattern of reduced cerebral metabolic rate for glucose (rCMRglc) has been shown by positron emission tomography (PET) in patients with dementia of the Alzheimer type. To verify if a similar rCMRglc pattern is present in subjects 'at risk' for Alzheimer's disease (AD), we used high-resolution PET to longitudinally study a subject with isolated memory impairment and a family history for autosomal dominant AD. Initial rCMRglc data did not reveal any consistent abnormality as compared to a group of sex- and age-matched healthy controls. However, 1 year later, a follow-up evaluation did reveal reduced parietal rCMRglc values coinciding with a worsening of cognitive impairment, which suggested that standard analyses of resting rCMRglc data may not be useful in the early diagnosis of AD. In contrast, when a previously determined discriminant function for distinguishing controls from AD patients was applied, the subject was correctly identified as an AD patient on both PET scans.

Aged↗