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Scott D Moffat

Publications and source records attributed to Scott D Moffat.

7 recordsLinked to original sources
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↗
PubMed2006

Long-term measures of free testosterone predict regional cerebral blood flow patterns in elderly men.

We previously reported that high circulating free testosterone (T) was associated with better performance on tests of memory, executive function, and spatial ability, and with a reduced risk for Alzheimer's disease. In this study, we report that free T levels, measured on multiple occasions over 14 years, predict regional cerebral blood flow (rCBF) measured by PET in 40 older men. Voxel-based regression, indicated that higher Free T was associated with increased rCBF in the hippocampus bilaterally (extending to the parahippocampal gyrus on the right), anterior cingulate gyrus, and right inferior frontal cortex. Total T concentrations were positively correlated with rCBF in the left putamen, bilateral thalamus, and left inferior frontal cortex and negatively correlated with amygdala rCBF bilaterally. These findings suggest that endogenous T influences brain physiology in regions critical for memory and attention and provide one mechanism through which T may affect cognitive function.

Aged↗
PubMed2005

Age differences in the neural systems supporting human allocentric spatial navigation.

Age-related declines in spatial navigation are well-known in human and non-human species. Studies in non-human species suggest that alteration in hippocampal and other neural circuitry may underlie behavioral deficits associated with aging but little is known about the neural mechanisms of human age-related decline in spatial navigation. The purpose of the present study was to examine age differences in functional brain activation during virtual environment navigation. Voxel-based analysis of activation patterns in young subjects identified activation in the hippocampus and parahippocampal gyrus, retrosplenial cortex, right and left lateral parietal cortex, medial parietal lobe and cerebellum. In comparison to younger subjects, elderly participants showed reduced activation in the hippocampus and parahippocampal gyrus, medial parietal lobe and retrosplenial cortex. Relative to younger participants elderly subjects showed increased activation in anterior cingulate gyrus and medial frontal lobe. These results provide evidence of age specific neural networks supporting spatial navigation and identify a putative neural substrate for age-related differences in spatial memory and navigational skill.

Adult↗
PubMed2005

Effects of testosterone on cognitive and brain aging in elderly men.

Older age is associated with functional declines throughout the body, including some aspects of cognitive performance. While dementia develops in only some elderly individuals, declines in cognitive functioning have an impact on daily living for many others. There are individual differences in age-related cognitive changes, however, and the factors that contribute to this variability have not been well-characterized. Recent evidence suggesting that age-related alterations in the endocrine environment may modulate cognitive changes has generated considerable interest. Currently, there is a discordance between the rapidly expanding number of studies of the possible neuroprotective effects of estrogens in postmenopausal women, and the relative dearth of analogous research on the putative effects of testosterone on cognitive and brain function in older men. This paper reviews the extant literature and reports new findings on the effects of testosterone loss and supplementation on cognitive and brain function in elderly men. Preliminary evidence suggests that testosterone loss may be a risk factor for cognitive decline and possibly for dementia. Conversely, the maintenance of higher testosterone levels either endogenously or through exogenous supplementation may prove beneficial for cognitive and brain function in elderly men. However, most studies are associational in nature and the intervention studies are of short-duration testosterone exposure in small samples of subjects. Large-scale placebo-controlled intervention studies are required to resolve ambiguities in the literature. Testosterone intervention to ameliorate cognitive decline may be warranted only when the efficacy and safety of longer-term use is firmly established.

Adult↗
PubMed2002

Effects of age on virtual environment place navigation and allocentric cognitive mapping.

This study assessed age differences in navigational behavior in a virtual Morris water maze (vMWM) and examined the ability of older adults to develop cognitive maps after vMWM experience. Compared with younger participants, older volunteers traversed a longer linear distance to locate the hidden platform. On the probe trial, younger volunteers spent a greater proportion of their total distance traveled in proximity to the platform and had more platform intersections. Analysis of map reproductions demonstrated that older participants used proximal objects to locate the goal but did not use room-geometry cues to aid navigation. These findings demonstrate age-related deficits on a laboratory measure of place learning and suggest that deficiencies in allocentric mapping may contribute to these deficits.

Adult↗
PubMed2002

Longitudinal assessment of serum free testosterone concentration predicts memory performance and cognitive status in elderly men.

Circulating testosterone (T) levels have behavioral and neurological effects in both human and nonhuman species. Both T concentrations and neuropsychological function decrease substantially with age in men. The purpose of this prospective, longitudinal study was to investigate the relationships between age-associated decreases in endogenous serum T and free T concentrations and declines in neuropsychological performance. Participants were volunteers from the Baltimore Longitudinal Study of Aging, aged 50-91 yr at baseline T assessment. Four hundred seven men were followed for an average of 10 yr, with assessments of multiple cognitive domains and contemporaneous determination of serum total T, SHBG, and a free T index (FTI). We administered neuropsychological tests of verbal and visual memory, mental status, visuomotor scanning and attention, verbal knowledge/language, visuospatial ability, and depressive symptomatology. Higher FTI was associated with better scores on visual and verbal memory, visuospatial functioning, and visuomotor scanning and a reduced rate of longitudinal decline in visual memory. Men classified as hypogonadal had significantly lower scores on measures of memory and visuospatial performance and a faster rate of decline in visual memory. No relations between total T or the FTI and measures of verbal knowledge, mental status, or depressive symptoms were observed. These results suggest a possible beneficial relationship between circulating free T concentrations and specific domains of cognitive performance in older men.

Aged↗