Biomedical subjects
D S Geldmacher
Publications and source records attributed to D S Geldmacher.
Effects of stimulus number and target-to-distractor ratio on the performance of random array letter cancellation tasks.
Cancellation tests are commonly used in the clinical assessment of visuospatial function, but there has been little study of task characteristics influencing performance. This study was designed to assess factors which affect cancellation performance. Sixteen healthy subjects sequentially performed four random-array letter cancellation tasks. The forms contained 50 and 100 stimuli and target:distractor (T/D) ratios of 1:4 and 1:9 with target letter "A" and randomly selected letter distractors. The primary performance measure was calculated as the number of correctly cancelled targets divided by the time to complete the task, corrected for accuracy. This measure revealed a strong effect of T/D ratio (p < .0001), with performance adversely affected by higher proportion of distractors. There was no effect of stimulus number. This suggests that T/D ratio should be considered in cancellation test design and interpretation.
Visual field influence on radial line bisection.
An attentional bias toward far peripersonal space has been proposed as the mechanism underlying inaccurate bisection of lines oriented radially in the sagittal plane. The position of stimuli in the visual scene has also been proposed as an important determinant of visual attention. This study was designed to evaluate the relative contributions of spatial and visual field factors in bisection of radial lines. The usual linkage of distant space and upper visual field was dissociated by assessing line bisection above eye level. Ten normal subjects bisected twelve 20-30-cm lines 35 cm above eye level and the identical stimuli 35 cm below the eyes. The previous findings of misbisection of radial lines distant to true center was replicated when stimuli were presented below eye level. Lines above eye level were misbisected significantly closer to the subjects. The findings suggest that visual field position influences the allocation of attention in the radial axis of space.
Pharmacotherapy for Alzheimer's disease.
Pharmacotherapy that is effective for AD is a major goal of extensive research programs throughout the world. With the approval of tacrine in the United States, an agent is now available that has demonstrated improvement in cognition for some AD patients. Other similar symptomatic therapies are likely to become available in the near future. In the long term, prevention and cure will be based on understanding pathogenesis, such as the genetic defects that can lead to disease in some families.
Fluoxetine in dementia of the Alzheimer's type: prominent adverse effects and failure to improve cognition.
Explore the source record for details and available documents.
Beta-amyloid activated microglia induce cell cycling and cell death in cultured cortical neurons.
Immunocytochemical studies of postmortem human tissue have shown that the neurons at risk for degeneration in Alzheimer's are marked by the ectopic expression of several cell cycle components. The current work investigates the roles that beta-amyloid activated microglia might play in leading neurons to re-express cell cycle components. Stable cultures of E16.5 mouse cortical neurons were exposed to beta-amyloid alone, microglial cells alone, or microglial cells activated by beta-amyloid. Increased cell death was found in response to each of these treatments, however, only the amyloid activated microglial treatment increased the number of neurons that were positive for cell cycle markers such as PCNA or cyclin D and incorporation of BrdU. Double labeling with BrdU and TUNEL techniques verified that the 'dividing' neurons were dying, most likely through an apoptotic mechanism. The identity of the soluble factor(s) elaborated by the microglia remains unknown, but FGF2, a suspected neuronal mitogen, was ruled out. These results further support a model in which microglial activation by beta-amyloid is a key event in the progression in Alzheimer's disease.
Realistic expectations for treatment success in Alzheimer's disease.
Alzheimer's disease (AD) is a progressive degenerative disease that warrants active management to delay or slow progression of its symptoms. The symptoms of AD encompass behavior and daily function as well as cognition, so clinicians should take a global view in the assessment of treatment success. Because there is currently no cure for AD, one cannot expect an initial cognitive improvement observed in the first few months of therapy to be sustained indefinitely. However, one should expect that the patient who is treated early and persistently with medication for AD will show less evidence of behavioral, functional, and cognitive deterioration over a period of time than one would expect in the absence of pharmacotherapy. Thus, treatment success includes not only short-term improvement of symptoms but also less decline over the long term. Determination of treatment success therefore also requires awareness of the typical progression of untreated AD. In this article we review the natural history of AD and evidence for the effectiveness of the treatments indicated for AD: donepezil, galantamine, rivastigmine, and memantine.