Dataset Information

Working memory and the organization of brain systems.

ABSTRACT: Working memory has historically been viewed as an active maintenance process that is independent of long-term memory and independent of the medial temporal lobe. However, impaired performance across brief time intervals has sometimes been described in amnesic patients with medial temporal lobe damage. These findings raise a fundamental question about how to know when performance depends on working memory and when the capacity for working memory has been exceeded and performance depends on long-term memory. We describe a method for identifying working memory independently of patient performance. We compared patients with medial temporal lobe damage to controls who were given either distraction or no distraction between study and test. In four experiments, we found concordance between the performance of patients and the effect of distraction on controls. The patients were impaired on tasks in which distraction had minimal effect on control performance, and the patients were intact on tasks in which distraction disrupted control performance. We suggest that the patients were impaired when the task minimally depended on working memory (and instead depended substantially on long-term memory), and they performed well when the task depended substantially on working memory. These findings support the conclusion that working memory (active maintenance) is intact after medial temporal lobe damage.

SUBMITTER: Shrager Y

PROVIDER: S-EPMC2426968 | biostudies-literature | 2008 Apr

REPOSITORIES: biostudies-literature

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Publications

Working memory and the organization of brain systems.

Shrager Yael Y Levy Daniel A DA Hopkins Ramona O RO Squire Larry R LR

The Journal of neuroscience : the official journal of the Society for Neuroscience 20080401 18

Working memory has historically been viewed as an active maintenance process that is independent of long-term memory and independent of the medial temporal lobe. However, impaired performance across brief time intervals has sometimes been described in amnesic patients with medial temporal lobe damage. These findings raise a fundamental question about how to know when performance depends on working memory and when the capacity for working memory has been exceeded and performance depends on long-t ...[more]

PMID: 18448658

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Project description:Ample research in visual working memory (VWM) has demonstrated that the memorized items are maintained in integrated spatial configurations, even when the spatial context is task irrelevant. These insights were obtained in studies in which participants were provided with the information they memorized. However, the encoding of provided information is only one aspect of memory. In everyday life, individuals often construct their own memory representations, an aspect of memory we have previously termed self-initiated (SI) working memory. In this study, we employed a SI VWM task in which participants selected the visual targets they memorized. The spatial locations of the targets were task irrelevant. Nevertheless, we were interested to see whether participants would construct spatially structured memory representations, which would suggest that they intended to maintain the visual targets as integrated spatial configurations. The results of two experiments demonstrated that participants constructed spatially structured configurations relative to random displays. Specifically, participants selected visual targets in close spatial proximity and constructed spatial sequences with short distances and fewer path crossings. When asked to construct configurations for a hypothetical competitor in a memory contest, participants disrupted the spatial structure by selecting visual targets that were further apart and by increasing the distances between them, which suggests that these characteristics were under their control. At the end of each experiment, participants provided verbal descriptions of the strategies they used to construct the memory displays. While the spatial structure of the SI memory representations was robust, it was absent from the participants' explicit descriptions, which focused on non-spatial strategies. Participants reported selecting items based, most frequently, on semantic categories and visual features. Taken together, these results demonstrated that participants had access to the metacognitive knowledge on the spatial structure of VWM representations, knowledge they manipulated to construct memory representations that enhanced or disrupted memory performance. While having a profound impact on behavior, this metacognitive knowledge on spatial structure remained implicit, as it was absent from the participants' verbal reports. Viewed from a larger perspective, this study explores how individuals interact with the world by actively structuring their surroundings to maximize cognitive performance.

Project description:Given prior reports of adverse effects of cannabis use on working memory, an executive function with a protracted developmental course during adolescence, we examined associations between developmental patterns of cannabis use and adult working memory (WM) processes. Seventy-five adults with longitudinal assessments of cannabis use (60 with reported use, 15 with no reported use) and prenatal drug exposure assessment completed a spatial WM task during fMRI at age 28. All subjects passed a multi-drug urine screen on the day of testing and denied recreational drug use in the past week. A fast event-related design with partial trials was used to separate the BOLD response associated with encoding, maintenance, and retrieval periods of the WM task. Behavioral results showed that subjects who began using cannabis earlier in adolescence had longer reaction times (RT) than those with later initiation. Cannabis age of onset was further associated with reduced posterior parietal cortex (PPC) encoding BOLD activation, which significantly mediated age of onset WM RT associations. However, cannabis age of onset brain-behavior associations did not differ between groups with a single reported use and those with repeated use, suggesting age of onset effects may reflect substance use risk characteristics rather than a developmentally-timed cannabis exposure effect. Within repeated cannabis users, greater levels of total cannabis use were associated with performance-related increases in dorsolateral prefrontal cortex (DLPFC) activation during maintenance. This pattern of significant results remained unchanged with inclusion of demographic and prenatal measures as covariates. Surprisingly, however, at the group level, cannabis users generally performed better than participants who reported never using cannabis (faster RT, higher accuracy). We extend previous investigations by identifying that WM associations with cannabis age of onset may be primary to PPC stimulus encoding activity, while the amount of cannabis use is associated with DLPFC maintenance processes. Poorer performance of participants who reported never using cannabis and the consistency of cannabis age of onset associations across single and repeated users limit interpretation of direct developmental effects of cannabis on WM in adulthood.

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Dataset Information

Working memory and the organization of brain systems.

Publications

Working memory and the organization of brain systems.

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