Biomedical subjects

David J Hardy

Publications and source records attributed to David J Hardy.

4 recordsLinked to original sources

PubMed2002

Multiple grid methods for classical molecular dynamics.

Presented in the context of classical molecular mechanics and dynamics are multilevel summation methods for the fast calculation of energies/forces for pairwise interactions, which are based on the hierarchical interpolation of interaction potentials on multiple grids. The concepts and details underlying multigrid interpolation are described. For integration of molecular dynamics the use of different time steps for different interactions allows longer time steps for many of the interactions, and this can be combined with multiple grids in space. Comparison is made to the fast multipole method, and evidence is presented suggesting that for molecular simulations multigrid methods may be superior to the fast multipole method and other tree methods.

Algorithms↗

PubMed2002

Reaction time slowing in adults with HIV: results of a meta-analysis using brinley plots.

A meta-analysis in the form of Brinley plots was conducted on the mean reaction times of HIV+ and HIV- groups. HIV+ reaction times were regressed on HIV- reaction times across 122 task conditions from 29 studies, producing a highly linear function (r(2) = .94), with a slope b = 1.039, which was not significantly different than b = 1.00. Asymptomatic and symptomatic HIV+ reaction times were also separately regressed on HIV- reaction times across 67 task conditions from 13 studies. Both functions were highly linear (r(2) = .97 and.90 respectively), with slopes of 1.034 and 1.117 respectively. Only the slope for symptomatic HIV+ groups was significantly larger than b = 1.00, suggesting a modest generalized slowing of cognition in these adults.

Adult↗

PubMed2002

Verbal and spatial working memory performance among HIV-infected adults.

Subtypes of working memory performance were examined in a cohort of 50 HIV-infected adults and 23 uninfected controls using an n-back paradigm (2-back) in which alphabetic stimuli were quasi-randomly presented to a quadrant of a computer monitor. In the verbal working memory condition, participants determined whether each successive letter matched the letter that appeared two previously in the series, regardless of spatial location. In the spatial working memory condition, participants determined whether each letter matched the spatial location of the letter that had appeared two previously, regardless of letter identity. The dependent variable was percent accuracy in each condition. Results of mixed model ANOVA revealed that the HIV-infected participants performed significantly worse than controls on both the verbal and spatial working memory tasks. A significant main effect for working memory condition was also present with both participant groups performing better on the spatial working memory task. These results, the first study of HIV-infected adults to directly compare verbal versus spatial working memory performance using the identical test stimuli across task conditions, suggests that HIV infection is associated with a decrement in working memory efficiency that is equally apparent for both verbal and spatial processing. These findings implicate central executive dysfunction as a likely substrate and provide the basis for hypothesizing that decline in working memory may contribute to other HIV-associated neuropsychological deficits.

Adult↗

PubMed2002

Reaction time performance in adults with HIV/AIDS.

Infection with the Human Immunodeficiency Virus-Type 1 (HIV-1) has been shown to lead to cognitive decline in a substantial proportion of infected adults. The characteristic neuropsychological symptomatology includes memory dysfunction, higher order attentional disturbance, executive dysfunction and, most relevant to this manuscript, cognitive slowing. This paper reviews the extant literature on reaction time (RT) performance in HIV-infected adults with an emphasis on mental chronometry. In addition to discussing studies of simple and choice RT, we also examine the utility of RT paradigms in the assessment of selective attention, covert orienting, sustained attention, divided attention, working memory, and implicit memory. Studies documenting the utility of RT tasks to track treatment response are also introduced. In aggregate, research to date that has employed RT tasks in the evaluation of HIV-infected patients has found that HIV infection leads to a mild degree of cognitive slowing that tends to worsen with increasing disease severity. It needs to be noted, however, that a significant percentage of studies failed to find HIV infection to lead to RT slowing. Results of Brinley plot analyses, a technique that shares commonalities with meta-analysis, reveal that HIV-infected patients diagnosed with AIDS are on an average 22% slower than uninfected controls. This paper also reviews data that has shown that HIV associated cognitive slowing, as indexed by single and dual choice RT, is amenable to pharmacologic intervention using the psychostimulant methylphenidate. Given the demonstrated sensitivity of RT tasks to the neuropsychological effects of HIV infection, it is recommended that RT tasks be included whenever possible in the routine clinical evaluation of HIV-infected patients.

Acquired Immunodeficiency Syndrome↗