Biomedical subjects

D Y Kimberg

Publications and source records attributed to D Y Kimberg.

4 recordsLinked to original sources

PubMed2001

Cortical effects of bromocriptine, a D-2 dopamine receptor agonist, in human subjects, revealed by fMRI.

Studies of human subjects performing cognitive tasks on and off dopaminergic drugs have suggested a specific role of dopamine in cognitive processes, particularly in working memory and prefrontal "executive" functions. However, the cortical effects of these drugs have been poorly understood. We used functional magnetic resonance imaging (fMRI) to examine both task-specific and general changes in cortical activity associated with bromocriptine, a selective agonist for D-2 dopamine receptors. Bromocriptine resulted in task-specific modulations of task-related activity in three cognitive tasks. Across tasks, the overall effect of the drug was to reduce task-related activity. We also observed drug effects on behavior that correlated with individual differences in memory span. We argue that bromocriptine may show both task-specific modulation and task-general inhibition of neural activity due to dopaminergic neurotransmission.

Adult↗

PubMed2000

Modulation of task-related neural activity in task-switching: an fMRI study.

Task-switching paradigms, in which subjects are typically asked to switch between different S-R mappings, can be considered operationalizations of executive control. Such paradigms are therefore potentially useful in investigating the neural bases of control functions. Here, we present the results of an fMRI study intended to examine two separable components of task-switching: preparation, and the residual shift cost identified by Rogers and Monsell [13]. In analyses restricted to functionally identified regions of interest, we found robust evidence of greater activity for switch trials, compared to repeat trials. This pattern was present both at the time of stimulus presentation and prior to the switch trial. In analyses of the entire brain, we were able to identify one area in the superior parietal lobule that was active during switching but was not part of the apparent network of task-related regions. We conclude that switch trials are neurally distinct from repeat trials in eliciting generally greater neural activity both before and during the performance of a trial.

Adult↗

PubMed1997

Effects of bromocriptine on human subjects depend on working memory capacity.

Pharmacological manipulation of brain dopamine concentration affects visuospatial working memory in humans and in animals, the latter effects localized to the prefrontal cortex. However, the effects of dopamine agonists on humans are poorly understood. We hypothesized that bromocriptine would have an effect on cognitive functions associated with the prefrontal cortex via its effects on cortical dopamine receptors and on subcortical receptors in areas that project to the neocortex. We found that the effect of bromocriptine on young normal subjects depended on the subjects' working memory capacity. High-capacity subjects performed more poorly on the drug, while low-capacity subjects improved. These results demonstrate an empirical link between a dopamine-mediated working memory system and higher cognitive function in humans.

Association Learning↗

PubMed1993

A unified account of cognitive impairments following frontal lobe damage: the role of working memory in complex, organized behavior.

A computer model is presented that performs 4 tasks sometimes impaired by frontal damage: motor sequencing, the Stroop task, the Wisconsin Card Sorting Test, and a context memory task. In each task, patterns of performance typical of frontal-damaged patients are shown to result from the same type of damage to the model, specifically, weakening of associations among elements in working memory. The simulation shows how a single underlying type of damage could result in impairments on a variety of seemingly distinct tasks. Furthermore, the hypothesized damage affects the processing components that carry out the task rather than a distinct central executive.

Brain Diseases↗