Biomedical subjects

Kristen M Kennedy

Publications and source records attributed to Kristen M Kennedy.

8 recordsLinked to original sources

PubMed2006

Fragmented pictures revisited: long-term changes in repetition priming, relation to skill learning, and the role of cognitive resources.

BACKGROUND: Whereas age-related declines in declarative memory have been demonstrated in multiple cross-sectional and longitudinal studies, the effect of age on non-declarative manifestations of memory, such as repetition priming and perceptual skill learning, are less clear. The common assumption, based on cross-sectional studies, is that these processes are only mildly (if at all) affected by age. OBJECTIVE: To investigate long-term changes in repetition priming and age-related differences in identification of fragmented pictures in a 5-year longitudinal design. METHOD: Healthy adults (age 28-82 years) viewed drawings of objects presented in descending order of fragmentation. The identification threshold (IT) was the highest fragmentation level at which the object was correctly named. After a short interval, old pictures were presented again along with a set of similar but novel pictures. Five years later the participants repeated the experiment. RESULTS: At baseline and 5-year follow-up alike, one repeated exposure improved IT for old (priming) and new (skill acquisition) pictures. However, long-term retention of priming gains was observed only in young adults. Working memory explained a significant proportion of variance in within-occasion priming, long-term priming, and skill learning. CONCLUSION: Contrary to cross-sectional results, this longitudinal study suggests perceptual repetition priming is not an age-invariant phenomenon and advanced age and reduced availability of cognitive resources may contribute to its decline.

Adult↗

PubMed2006

Extrahippocampal contributions to age differences in human spatial navigation.

The hippocampus (HC) and associated neural structures are hypothesized to contribute to individual differences in human spatial navigation. However, functional imaging studies and theoretical models underscore the importance of extrahippocampal regions as well. The purpose of the present study was to examine age differences in virtual environment navigation and to assess possible relationships between navigation and structural integrity of hippocampal and extrahippocampal brain regions. Healthy adult volunteers completed a virtual navigation task and underwent magnetic resonance imaging to assess volumes of the caudate nucleus (CN), cerebellum, HC, prefrontal, and primary visual cortices. Results demonstrated robust age-related differences in place learning. Moreover, individual differences in regional brain volumes as well as performance on the tests of memory and executive functions contributed to age differences in human place learning. High performance in a virtual navigation task was associated with larger volume of the CN and prefrontal gray and white matter. Larger hippocampal volume was associated with improved performance in the young but not old participants. We conclude that human navigation requires both hippocampal and extrahippocampal brain systems and draws on executive resources for successful performance.

Adult↗

PubMed2005

Regional brain changes in aging healthy adults: general trends, individual differences and modifiers.

Brain aging research relies mostly on cross-sectional studies, which infer true changes from age differences. We present longitudinal measures of five-year change in the regional brain volumes in healthy adults. Average and individual differences in volume changes and the effects of age, sex and hypertension were assessed with latent difference score modeling. The caudate, the cerebellum, the hippocampus and the association cortices shrunk substantially. There was minimal change in the entorhinal and none in the primary visual cortex. Longitudinal measures of shrinkage exceeded cross-sectional estimates. All regions except the inferior parietal lobule showed individual differences in change. Shrinkage of the cerebellum decreased from young to middle adulthood, and increased from middle adulthood to old age. Shrinkage of the hippocampus, the entorhinal cortices, the inferior temporal cortex and the prefrontal white matter increased with age. Moreover, shrinkage in the hippocampus and the cerebellum accelerated with age. In the hippocampus, both linear and quadratic trends in incremental age-related shrinkage were limited to the hypertensive participants. Individual differences in shrinkage correlated across some regions, suggesting common causes. No sex differences in age trends except for the caudate were observed. We found no evidence of neuroprotective effects of larger brain size or educational attainment.

Adult↗

PubMed2005

Age, sex and regional brain volumes predict perceptual-motor skill acquisition.

Neural mechanisms of skill acquisition across the lifespan are largely unknown. Neuroimaging in younger adults and research on neurodegenerative disorders suggests that perceptual-motor learning relies on the striatum, cerebellum, and prefrontal cortex. Our objective in this study was to explore whether individual differences in regional brain volumes modify the effects of age and sex on the acquisition of a perceptual-motor skill in healthy adults. The participants (N = 85, age 22-80) performed five 5-trial blocks of a mirror-drawing task on three separate days (for a total of 25 trials). Index of performance was time to completion and number of errors committed. All participants improved with practice, but younger adults performed better than their older counterparts, and women performed better than men. Four brain regions--lateral prefrontal cortex (LPFC), hippocampus (HC), cerebellar hemispheres (Cb) and the caudate nucleus (Cd)--were selected on the basis of the relevant literature and measured on MRI scans. All regional volumes were negatively associated with age, although the magnitude of association differed from LPFC (the strongest) to Cd (the weakest). Larger lateral PFC was associated with better performance on the mirror drawing task, and this link was stronger in the older participants and was strengthened at the later stages of learning. Larger caudate was related to better performance, especially at later learning, among men, but among women the link was evident only during early learning. Thus, mirror-drawing represents a task that, despite its visual-spatial nature, favors women, and may exhibit sexually dimorphic brain substrates.

Adult↗

PubMed2005

Aging and longitudinal change in perceptual-motor skill acquisition in healthy adults.

Knowledge about aging of perceptual-motor skills is based almost exclusively on cross-sectional studies. We examined age-related changes in the retention of mirror-tracing skills in healthy adults who practiced for 3 separate days at baseline and retrained 5 years later at follow-up. Overall, the speed and accuracy of an acquired skill were partially retained after a 5-year interim, although the same asymptote was reached. Analyses with individual learning curves indicated that the effects of age on mirror-tracing speed were greater at longitudinal follow-up than at baseline, with older adults requiring more training to reach asymptote. Thus, although the long-term retention of acquired skills declines with age, older adults still retain the ability to learn the skill. Moreover, those who maintained a processing speed comparable with that of the younger participants evidenced no age-related performance decrements on the mirror-drawing task.

Adult↗

PubMed2004

Hormone replacement therapy and age-related brain shrinkage: regional effects.

Neuroprotective properties of estrogen have been established in animal models, but clinical trials of hormone replacement therapy (HRT) produced contradictory results. We examined the impact of HRT on age-related regional changes in human brain volume. Six brain regions were measured twice, five years apart, in 12 healthy women who took HRT and in matched controls who did not. The controls showed a typical pattern of differential brain shrinkage in the association cortices and the hippocampus with no change in the primary visual cortex. In contrast, women who took HRT showed comparable shrinkage of the hippocampus but no significant shrinkage of the neocortex. Future large scale studies may benefit from applying regional rather than global measures in assessment of brain integrity.

Aged↗

PubMed2003

Differential age-related changes in the regional metencephalic volumes in humans: a 5-year follow-up.

We examined changes in the metencephalon of healthy adults who underwent magnetic resonance imaging twice, 5 years apart. The volumes of the cerebellar hemispheres, anterior and posterior vermis, declive-folium-tuber of the vermis, and the ventral pons were measured by operators unaware of subjects' characteristics and the time of scan. The cerebellar hemispheres and the cerebellar vermis, but not the ventral pons, were smaller in older people at both measurements. Significant linear shrinkage was observed in all examined metencephalic regions. Annualized rate of shrinkage was the greatest in the cerebellar hemispheres, somewhat smaller in the vermis, and minimal in the pons. Neither sex differences, nor sex-specific aging trends were found. We conclude that differential age-related shrinkage of the metencephalic structures occurs in healthy adults, but its magnitude differs from cross-sectional estimates.

Adult↗

PubMed2003

Differential aging of the human striatum: longitudinal evidence.

BACKGROUND AND PURPOSE: Information about age-related changes in the striatum comes almost exclusively from cross-sectional studies. We examined age-related differences and longitudinal changes in the volume of the striatal nuclei, compared longitudinal measures of changes with their cross-sectional estimates, and addressed the question of differential aging of the basal ganglia. METHODS: We measured the volumes of the caudate nucleus (head), the putamen, and the globus pallidus on MR images of 53 healthy adults whose ages at baseline ranged between 20 and 77 years. The measurements were conducted twice, 5 years apart. RESULTS: On both measurement occasions, the volume of the neostriatal nuclei (caudate and putamen) but not of the globus pallidus correlated negatively with age. However, longitudinal comparison revealed significant declines in the neostriatal volumes and smaller (but statistically significant) shrinkage of the paleostriatum. In 5 years, the striatal components (caudate, putamen, and globus pallidus) shrunk by 1.21, 0.85, and 0.55 standard deviation units, respectively. The average annual shrinkage rate was 0.83% in the caudate nucleus, 0.73% in the putamen, and 0.51% in the globus pallidus. CONCLUSION: Although cross-sectional estimates suggested preservation of some striatal nuclei, longitudinal shrinkage of the whole striatum was evident even in a selected group of healthy adults. Moreover, the magnitude of observed longitudinal change was greater than predicted from cross-sectional studies.

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