Biomedical subjects

Sasha E B Gibbs

Publications and source records attributed to Sasha E B Gibbs.

3 recordsLinked to original sources

PubMed2006

Is the prefrontal cortex necessary for delay task performance? Evidence from lesion and FMRI data.

Although the prefrontal cortex (PFC) is consistently found to be associated with various working memory processes, the necessity of the PFC for such processes remains unclear. To elucidate PFC contributions to storage and rehearsal/maintenance processes engaged during verbal working memory function, we assessed behavior of patients with lesions to the left or right lateral PFC, and neural activity of healthy young subjects during fMRI scanning, during performance of working memory tasks. We found that PFC lesions did not affect storage processes--which is consistent with the notion that posterior cortical networks can support simple retention of information. We also found that PFC lesions did not affect rehearsal/maintenance processes, which was in contrast to our finding that healthy subjects performing a verbal delayed recognition task showed bilateral PFC activation. These combined imaging and behavioral data suggest that working memory rehearsal/maintenance processes may depend on both hemispheres, which may have implications for recovery of function and development of rehabilitation therapies after frontal injury.

Adolescent↗

PubMed2005

A functional MRI study of the effects of bromocriptine, a dopamine receptor agonist, on component processes of working memory.

RATIONALE: Dopamine is abundant in the prefrontal cortex and striatum, regions implicated in working memory processes. Monkey studies suggest that subpopulations of prefrontal neurons are sensitive to component processes of working memory, and that dopaminergic actions at D1 and D2 receptors differentially affect these neurons. However, it is not known to what extent the effects of dopaminergic stimulation may differ in human subjects across the processing stages of working memory, and whether these effects are found throughout the network of task-related brain regions. OBJECTIVE: In this study we tested the effects of the D2 dopamine agonist bromocriptine during the performance of a delayed recognition task using functional magnetic resonance imaging (fMRI). METHODS: We measured blood oxygenation level dependent (BOLD) signals as subjects performed a spatial and object delayed recognition task. Subjects were scanned twice, once following 1.25 mg of bromocriptine and once following lactose placebo in a randomized double-blind design. Using an event-related design allowed for separate investigation of encoding, delay, and response period effects of dopaminergic stimulation. RESULTS: A group analysis revealed that bromocriptine treatment decreased activity in the task network at encoding and increased activity at response. There was no clear pattern of change in the delay period network. Across subjects, these BOLD signal changes were accompanied by reductions in accuracy and increases in response time during delayed recognition for spatial and object information. CONCLUSIONS: Decreased activity during encoding suggests that hyperdopaminergic stimulation may have reduced stimulus encoding processes, contributing to impaired performance.

Adult↗

PubMed2005

Individual capacity differences predict working memory performance and prefrontal activity following dopamine receptor stimulation.

Dopamine receptors are abundant in the prefrontal cortex (PFC), a critical region involved in working memory. This pharmacological fMRI study tested the relationships between dopamine, PFC function, and individual differences in working memory capacity. Subjects performed a verbal delayed-recognition task after taking either the dopamine receptor agonist bromocriptine or a placebo. Behavioral effects of bromocriptine treatment depended on subjects' working memory spans, with the greatest behavioral benefit for lower span subjects. After bromocriptine, PFC activity was positively correlated with a measure of cognitive efficiency (RT slope) during the probe period of the task. Less efficient subjects with slower memory retrieval rates had greater PFC activity, whereas more efficient subjects had less activity. After placebo, these measures were uncorrelated. These results support the role of dopamine in verbal working memory and suggest that dopamine may modulate the efficiency of retrieval of items from the contents of working memory. Individual differences in PFC dopamine receptor concentration may thus underlie the behavioral effects of dopamine stimulation on working memory function.

Adult↗