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Sustained and transient neural modulations in prefrontal cortex related to declarative long-term memory, working memory, and attention.
Umeå University, Faculty of Social Sciences, Psychology.
Umeå University, Faculty of Social Sciences, Psychology.
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2007 (English)In: Cortex, ISSN 0010-9452, Vol. 43, no 1, 22-37 p.Article in journal (Refereed) Published
Abstract [en]

Common activations in prefrontal cortex (PFC) during episodic and semantic long-term memory (LTM) tasks have been hypothesized to reflect functional overlap in terms of working memory (WM) and cognitive control. To evaluate a WM account of LTM-general activations, the present study took into consideration that cognitive task performance depends on the dynamic operation of multiple component processes, some of which are stimulus-synchronous and transient in nature; and some that are engaged throughout a task in a sustained fashion. PFC and WM may be implicated in both of these temporally independent components. To elucidate these possibilities we employed mixed blocked/event-related functional magnetic resonance imaging (fMRI) procedures to assess the extent to which sustained or transient activation patterns overlapped across tasks indexing episodic and semantic LTM, attention (ATT), and WM. Within PFC, ventrolateral and medial areas exhibited sustained activity across all tasks, whereas more anterior regions including right frontopolar cortex were commonly engaged in sustained processing during the three memory tasks. These findings do not support a WM account of sustained frontal responses during LTM tasks, but instead suggest that the pattern that was common to all tasks reflects general attentional set/vigilance, and that the shared WM-LTM pattern mediates control processes related to upholding task set. Transient responses during the three memory tasks were assessed relative to ATT to isolate item-specific mnemonic processes and were found to be largely distinct from sustained effects. Task-specific effects were observed for each memory task. In addition, a common item response for all memory tasks involved left dorsolateral PFC (DLPFC). The latter response might be seen as reflecting WM processes during LTM retrieval. Thus, our findings suggest that a WM account of shared PFC recruitment in LTM tasks holds for common transient item-related responses rather than sustained state-related responses that are better seen as reflecting more general attentional/control processes.

Place, publisher, year, edition, pages
2007. Vol. 43, no 1, 22-37 p.
Keyword [en]
Adult, Attention/*physiology, Cognition/physiology, Discrimination Learning/physiology, Evoked Potentials/physiology, Female, Humans, Magnetic Resonance Imaging, Male, Memory/*physiology, Mental Processes/physiology, Neurons/*physiology, Prefrontal Cortex/cytology/*physiology, Psychomotor Performance/physiology, Reference Values, Verbal Learning/*physiology, Visual Perception/physiology
URN: urn:nbn:se:umu:diva-12524PubMedID: 17334205OAI: diva2:152195
Available from: 2008-06-19 Created: 2008-06-19 Last updated: 2011-01-25Bibliographically approved
In thesis
1. Cross-functional brain imaging of attention, memory, and executive functions: Unity and diversity of neurocognitive component processes
Open this publication in new window or tab >>Cross-functional brain imaging of attention, memory, and executive functions: Unity and diversity of neurocognitive component processes
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The central theme of the present thesis revolves around the exploration of similarities and differences in brain activity patterns invoked by the component processes underlying mnemonic, executive and attentional functions. The primary aim was to identify and functionally characterize commonly recruited brain regions in terms of shared component processes, which has been a largely neglected area of research in cognitive neuroscience. The vast majority of functional brain imaging investigations of cognition has focused on delineating differences between cognitive functions or processes, with the purpose of isolating the unique functional neuroanatomy that underlies specific cognitive domains. By contrast, the present thesis builds on the results from three imaging studies that focused primarily on detecting commonalities in functional brain activity across different forms of memory processes. In study I, the imaging data from two positron emission tomography (PET) experiments were re-analyzed to identify common activation patterns associated with nine different memory tasks incorporated across the experiments, three each separately indexing working memory, episodic memory, and semantic memory. A generic prefrontal cortex (PFC) network involving discrete subregions of the left hemisphere located in ventrolateral (BA 45/47), dorsolateral (BA 9/44/46), and frontopolar (BA 10) sectors of PFC, as well as a midline portion of the frontal lobes, encompassing the dorsal part of the anterior cingulate cortex (ACC) (BA 24/32), was conjointly recruited across all tasks. In study II, we used a novel mixed blocked/event-related functional magnetic resonance imaging (fMRI) design, which enables separation of brain responses associated with different temporal dynamics to further investigate commonalities of neural activation across working memory, episodic memory, semantic memory, and attention/vigilance. A similar set of common PFC regions, as that discovered in Study I, was found to elicit overlapping brain activity across all memory tasks, with a subset of regions also activated in the attention/vigilance task. Furthermore, the task-induced brain activity was dissociated in terms of the temporal profiles of the evoked neural responses. A common pattern of sustained activity seen across all memory tasks and the attention task involved bilateral (predominantly right-lateralized) ventrolateral PFC (BA 45/47), and the dorsal ACC (BA 24/32), which was assumed to reflect general processes of attention/vigilance. A pattern of sustained activity elicited in all memory tasks, in the absence of attention-related activity, involved the right frontopolar cortex (BA 10), which was assumed to reflect control processes underlying task set maintenance. In addition, common transient activation evoked in the memory tasks relative to the attention task was found in the dorsolateral (BA 9/44) and ventrolateral (BA 47) PFC, the superior parietal cortex (BA 7), and cerebellum. In study III, a mixed fMRI design was used to assess the degree of common brain activity associated with increased executive demand, which was independently manipulated within episodic and working memory. Unitary control modulations involved a shared tonic executive component subserved by fronto-striatal-cerebellar circuitry, assumed to govern top-down context processing throughout task periods, and a stimulus-synchronous phasic component mediated by the intraparietal sulcus (BA 7), assumed to support dynamic shifting of the ‘focus of attention’ among internal representations. Collectively, the theoretical implications of shared neural mechanisms are discussed, with a special focus on human memory and its multifaceted relationships with attention and executive control functions. Finally, the presented imaging data are used to outline a tentative hierarchical neurocognitive model that attempts to give an account of how different unitary component processes might work together during cognitive task performance.

Place, publisher, year, edition, pages
Umeå: Psykologi, 2006. 69 p.
Human memory, executive functions, prefrontal cortex, sustained and transient neural activity, declarative long-term memory, attention, working memory, functional neuroimaging, cognitive control.
National Category
urn:nbn:se:umu:diva-805 (URN)91-7264-107-X (ISBN)
Public defence
2006-06-01, Hörsal E, Humanisthuset, Umeå universitet, Umeå, 10:15
Available from: 2006-05-19 Created: 2006-05-19 Last updated: 2011-01-25Bibliographically approved

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