| 1. |
- Kompus, Kristiina, 1983-, et al.
(författare)
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Distinct control networks for cognition and emotion in the prefrontal cortex
- 2009
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Ingår i: Neuroscience Letters. - : Elsevier BV. - 0304-3940 .- 1872-7972. ; 467:2, s. 76-80
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Tidskriftsartikel (refereegranskat)abstract
- The activation of dorsolateral prefrontal cortex (dlPFC) has been suggested to reflect the engagement of a control mechanism for top-down biasing of context processing in resource-demanding memory tasks. Here we tested the hypothesis that the dlPFC subserves a similar function also in attention and emotion tasks. 18 healthy young adults were tested in a functional magnetic resonance imaging (fMRI) study where the demands for context processing were manipulated in three different cognitive domains: auditory attention, episodic retrieval, and emotion regulation. We found that the right dlPFC was jointly sensitive to increased cognitive demands in the attention and memory tasks. By contrast, increased demands in the emotion task (reappraisal) were associated with increased activity in ventromedial PFC along with decreased amygdala activity. Our findings of divergent prefrontal control networks for cognitive and emotional control extend previous separations of cognition and emotion in the anterior cingulate cortex.
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| 2. |
- Marklund, Petter, 1968-, et al.
(författare)
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Age effects on semantic coherence: Latent semantic analysis applied to letter fluency data
- 2009
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Ingår i: [Host publication title missing]. - 9780769538334 ; , s. 73-76
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Konferensbidrag (refereegranskat)abstract
- Abstract in UndeterminedWe investigated age-related changes in the semantic distance between successively generated words in two letter fluency tasks differing with respect to demands placed on executive control. The semantic distance was measured by Latent Semantic Analysis (LSA). The results show that older people have a larger semantic distance between successively generated items than young people, and that this effect is particularly pronounced in the more demanding fluency task. Taken together, our findings support the idea that elderly have a less distinct semantic network compared to young people while also demonstrating the feasibility of LSA as a powerful tool for delineating multifaceted aspects of semantic organization inherent in behavioural data from language production tasks.
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| 3. |
- Marklund, Petter
(författare)
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Cross-functional brain imaging of attention, memory, and executive functions : Unity and diversity of neurocognitive component processes
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 4. |
- Marklund, Petter, et al.
(författare)
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Intersecting the divide between working and episodic memory : evidence from sustained and transient brain activity patterns
- 2007
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Ingår i: The conitive neruoscience of working memory. - Oxford : Oxford University Press. - 9780191693816 - 9780198570394 ; , s. 305-332
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Bokkapitel (populärvet., debatt m.m.)abstract
- This chapter reviews positron emission tomography (PET), functional magnetic resonance imaging (fMRI), and event-related potential (ERP) studies of episodic memory retrieval, working memory and of executive control, and concludes that working memory may comprise a range of control functions linked with the operation of the prefrontal cortex that serve to retrieve information from long-term memory in more posterior areas and to maintain the information in an active state. This views the memory components of working memory as comprising the currently activated areas of long-term memory rather than a quite distinct temporary memory system.
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| 5. |
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| 6. |
- Marklund, Petter, et al.
(författare)
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Sustained and transient neural modulations in prefrontal cortex related to declarative long-term memory, working memory, and attention.
- 2007
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Ingår i: Cortex. - 0010-9452. ; 43:1, s. 22-37
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Marklund, Petter, 1968-, et al.
(författare)
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Temporal dynamics of basal ganglia under-recruitment in Parkinson's disease : transient caudate abnormalities during updating of working memory
- 2009
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Ingår i: Brain. - : Oxford University Press (OUP). - 0006-8950 .- 1460-2156. ; 132:2, s. 336-346
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Tidskriftsartikel (refereegranskat)abstract
- Using hybrid-blocked/event-related fMRI and the 2-back taskwe aimed to decompose tonic and phasic temporal dynamics ofbasal ganglia response abnormalities in working memory associatedwith early untreated Parkinson's disease. In view of the tonic/phasicdopamine hypothesis, which posits a functional division betweenphasic D2-dependent striatal updating processes and tonic D1-dependentprefrontal context-maintenance processes, we predicted thatnewly diagnosed, drug-naïve Parkinson's disease patients,with selective striatal dopamine deprivation, would demonstratetransient rather than sustained activation changes in the basalganglia during 2-back performance. Task-related activation patternswithin discrete basal ganglia structures were directly comparedbetween patients and healthy elderly controls. The obtainedresults yielded uniquely transient underactivation foci in caudatenuclei, putamen and globus pallidus in Parkinson's disease patients,which indicates suboptimal phasic implementation of striatalD2-dependent gating mechanisms during updating. Sustained underactivationwas only seen in the anterior putamen, which may reflect initialsigns of tonic control impairment. No significant changes wereexhibited in prefrontal cortex. The present findings resonatewell with the tonic/phasic dopamine account and suggest thatbasal ganglia under-recruitment associated with executive dysfunctionin early Parkinson's disease might predominantly stem from deficienciesin phasic executive components subserved by striatum.
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| 8. |
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| 9. |
- Nyberg, Lars, et al.
(författare)
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Striatal dopamine D2 binding is related to frontal BOLD response during updating of long-term memory representations
- 2009
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Ingår i: NeuroImage. - : Elsevier. - 1053-8119 .- 1095-9572. ; 46:4, s. 1194-1199
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Tidskriftsartikel (refereegranskat)abstract
- Multi-modal brain imaging was used to examine the relation between individual differences in resting-state striatal dopamine D2 binding and the magnitude of prefrontal BOLD activation during updating of long-term memory (LTM) representations. Increased activity in the left prefrontal cortex was observed when LTM updating was required, and there was a positive correlation between striatal D2 activity and the magnitude of left prefrontal activity during updating. These findings support predictions from neurocomputational models of a relation of dopaminergic neurotransmission to transient cognitive operations and related brain activity.
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