| 1. |
- Kompus, Kristiina
(författare)
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Default mode network gates the retrieval of task-irrelevant incidental memories
- 2011
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Ingår i: Neuroscience Letters. - : Elsevier. - 0304-3940 .- 1872-7972. ; 487:3, s. 318-321
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Tidskriftsartikel (refereegranskat)abstract
- Episodic memories can be retrieved by an intentional search for certain information. Alternatively, a past episode may enter our consciousness without any intention to retrieve it, prompted by a stimulus in our surroundings. Incidental retrieval does not occur upon each encounter with a familiar stimulus, suggesting that a gating mechanism exists which regulates incidental retrieval activity. We analyzed data from a functional magnetic resonance imaging study on incidental retrieval in healthy young adults and found that failure to incidentally retrieve was selectively associated with reduced activation of lateral and medial parietal regions as well as ventromedial frontal cortex, areas implicated in default mode network. This is the first demonstration that relative deactivation of the brain regions associated with the default mode gates the consciousness from currently irrelevant memories.
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| 2. |
- Kompus, Kristiina, et al.
(författare)
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Deficits in inhibitory executive functions in Klinefelter (47, XXY) syndrome
- 2011
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Ingår i: Psychiatry Research. - : Elsevier BV. - 0165-1781 .- 1872-7123. ; 189:1, s. 135-140
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Tidskriftsartikel (refereegranskat)abstract
- Klinefelter syndrome (47, XXY) is a sex chromosome aneuploidy associated with mild deficits in cognitive and language functions. Dysfunctions have also been reported in performance of tasks which examine executive functions. However, it is unclear whether the impaired performance is caused or accentuated by problems with semantic processing and information processing speed. In the present study we used an experimental task which is relatively insensitive to these confounding factors. We examined inhibitory executive functions in a group of XXY males compared with male (XY) and female (XX) controls, using a dichotic listening speech sound task with instructions to focus attention on either the right or the left ear stimulus. With this task, inhibitory executive functions can be assessed separately from language, processing speed, and attention orientation abilities. We found that XXY males showed a selective deficit in inhibitory executive functions compared to both control groups, whereas attentional orientation was not impaired. The present findings suggest that executive dysfunctions associated to Klinefelter syndrome can be selectively identified, and are particularly accentuated in the inhibitory sub-component. Such improved understanding of the nature of executive dysfunctions in XXY males may aid the development of specific neuropsychological rehabilitation strategies.
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| 3. |
- 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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| 4. |
- Kompus, Kristiina, 1983-, et al.
(författare)
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Dynamic switching between semantic and episodic memory systems
- 2009
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Ingår i: Neuropsychologia. - : Elsevier BV. - 0028-3932 .- 1873-3514. ; 47:11, s. 2252-2260
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Tidskriftsartikel (refereegranskat)abstract
- It has been suggested that episodic and semantic long-term memory systems interact during retrieval. Here we examined the flexibility of memory retrieval in an associative task taxing memories of different strength, assumed to differentially engage episodic and semantic memory. Healthy volunteers were pre-trained on a set of 36 face-name pairs over a 6-week period. Another set of 36 items was shown only once during the same time period. About 3 months after the training period all items were presented in a randomly intermixed order in an event-related fMRI study of face-name memory. Once presented items differentially activated anterior cingulate cortex and a right prefrontal region that previously have been associated with episodic retrieval mode. High-familiar items were associated with stronger activation of posterior cortices and a left frontal region. These findings fit a model of memory retrieval by which early processes determine, on a trial-by-trial basis, if the task can be solved by the default semantic system. If not, there is a dynamic shift to cognitive control processes that guide retrieval from episodic memory.
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| 5. |
- Kompus, Kristiina, 1983-, et al.
(författare)
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Early analysis of retrieval cues guides selection of retrieval processing
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Human long-term memory holds semantic and episodic memories. Retrieval from these two memory systems occurs independently. As required information may be held in either of these systems, the question arises how and when is the choice of retrieval processing (episodic/semantic) determined. Here we report results from an ERP study on healthy young adults during a forced-choice associative recognition task, designed to test the hypothesis that early processing of retrieval cues influences subsequent retrieval processing. The test items had previously been encoded repeatedly (6x) or only once (1x) during pre-experimental training period, thereby influencing the reliance on semantic or episodic retrieval processes. Differences between the two conditions were observed for the familiarity-sensitive FN400 component as well as for a late (>1000 ms) component indexing post-retrieval processing. Most critically, we found that a difference between successfully retrieved 6x and 1x items emerged already during the 100-140 ms time window. These results indicate that choice of retrieval processes (episodic/semantic) depends on early matching between retrieval cues and memory traces.
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| 6. |
- Kompus, Kristiina, 1983-
(författare)
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How the past becomes present : neural mechanisms governing retrieval from episodic memory
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Remembering previously experienced events can happen as a result of an effortful retrieval attempt. At other occasions, a memory can enter our minds without any apparent effort – or, indeed, intention - to retrieve. Although it has long been appreciated that retrieval from episodic memory is intertwined with cognitive control, the neural mechanisms of memory-control interactions remain unclear. In this thesis I have used functional magnetic resonance imaging (fMRI) and scalp-recorded event-related potentials (ERP) to study the neural basis of episodic retrieval at varying levels of cognitive control. The dorsolateral prefrontal cortex (dlPFC) has been suggested to support a cognitive control mechanism (context processing) which is relevant during various situations that demand maintenance of current goals and rules. Although increased dlPFC recruitment with increasing context processing demands has been demonstrated during episodic retrieval, there are relatively few studies directly comparing the engagement of dlPFC during episodic retrieval with that during other task domains. In Study I, context processing demands were amplified in episodic retrieval, auditory attention and emotion regulation tasks. This led to overlapping dlPFC recruitment in the first two domains and a divergent reliance on ventromedial prefrontal cortex in the emotion domain. Thus, when selection between competing representations needs to be carried out in accordance with the currently relevant goals and task rules, the episodic memory system interacts with domain-general cognitive control mechanisms. Studies II and III explored the reactive nature of retrieval-specific control mechanisms: can we flexibly switch between semantic and episodic retrieval based on the information extracted from a retrieval cue? This was studied using a recognition memory task where the relevant information could with equal probability be supplied by the semantic or the episodic memory system. The fMRI results (Study II) showed that the brain activation during the ‘episodic’ but not the ‘semantic’ trials was expressed in the right prefrontal cortex. As the order of trials was unpredictable, the corresponding changes in brain activation might be evoked by differences in early cue-trace interactions. An event-related potential study (Study III) with the same experimental protocol as in Study II showed that neural processing corresponding to the two trial types diverged as early as in the time window 100-140 ms post-cue onset, thus highlighting the importance of early cue-trace matching in the selection of further retrieval processing. Study IV explored incidental episodic retrieval. Although this form of retrieval is a common experience in everyday life and a disturbing symptom in some psychiatric conditions, it is not clear how such spontaneous expressions of memory are initiated and to what extent the prefrontal cortex is engaged. The fMRI results showed, consistent with Study I, that dlPFC is specifically associated with the intention to retrieve, independently of success. Retrieval success engaged similar networks for incidentally as well as intentionally retrieved memories, comprising the hippocampus, precuneus, ventrolateral PFC, and the anterior cingulate cortex. Collectively, the fMRI and ERP results indicated that incidental retrieval was initiated by early (< 200 ms) oldness estimation carried out on the semantic information extracted from the retrieval cues. Taken together, the results of this thesis indicate that episodic retrieval can be initiated via two routes: a bottom-up input rising early during the cue processing, and a top-down input provided by the cognitive control processes mediated by the prefrontal cortex.
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| 7. |
- Kompus, Kristiina, 1983-, et al.
(författare)
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Multimodal imaging of incidental retrieval : the low route to memory
- 2011
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Ingår i: Journal of cognitive neuroscience. - : MIT Press - Journals. - 0898-929X .- 1530-8898. ; 23:4, s. 947-960
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Tidskriftsartikel (refereegranskat)abstract
- Memories of past episodes frequently come to mind incidentally, without directed search. It has remained unclear how incidental retrieval processes are initiated in the brain. Here we used fMRI and ERP recordings to find brain activity that specifically correlates with incidental retrieval, as compared to intentional retrieval. Intentional retrieval was associated with increased activation in the dorsolateral prefrontal cortex. By contrast, incidental retrieval was associated with a reduced fMRI signal in posterior brain regions, including extrastriate and parahippocampal cortex, and a modulation of a posterior ERP component 170 ms after the onset of visual retrieval cues. Successful retrieval under both intentional and incidental conditions was associated with increased activation in hippocampus, precuneus and ventrolateral prefrontal cortex, as well as increased amplitude of the P600 ERP component. These results demonstrate how early bottom-up signals from the posterior cortex can lead to reactivation of episodic memories in the absence of strategic retrieval attempts.
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| 8. |
- Kompus, Kristiina, et al.
(författare)
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The size of the anterior corpus callosum correlates with the strength of hemispheric encoding-retrieval asymmetry in the ventrolateral prefrontal cortex
- 2011
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Ingår i: Brain Research. - Amsterdam : Elsevier BV. - 0006-8993 .- 1872-6240. ; 1419, s. 61-67
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Tidskriftsartikel (refereegranskat)abstract
- Functional lateralization of episodic memory processes in the frontal lobe is an area of intense study in the field of cognitive neuroimaging. Yet, to date there is insufficient knowledge of what role the interhemispheric structural connectivity plays in this lateralized organization. We analyzed functional and structural magnetic resonance imaging data from healthy adult volunteers who performed an associative encoding and retrieval task. We examined the relationship between functional voxel-based relative asymmetry of encoding and retrieval in the frontal lobes and the size of the anterior corpus callosum (antCC; corrected for brain size). The size of the antCC was strongly associated to the relative encoding-retrieval asymmetry in the ventrolateral prefrontal cortex (BA 47). These findings show that the functional asymmetry of episodic memory processes in the frontal lobes is associated with the structural connectivity between the hemispheres.
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| 9. |
- Salami, Alireza, et al.
(författare)
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Characterizing the neural correlates of modality-specific and modality-independent accessibility and availability signals in memory using partial-least squares
- 2010
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Ingår i: NeuroImage. - : Elsevier BV. - 1053-8119 .- 1095-9572. ; 52:2, s. 686-698
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Tidskriftsartikel (refereegranskat)abstract
- Previous studies have shown that information that currently cannot be retrieved but will be retrieved on a subsequent, more supported task (i.e. is available but not accessible) has a distinct neural signature compared with non-available information. For verbal paired-associates, an availability signal has been revealed in left middle temporal cortex, an area potentially involved in the storage of such information, raising the possibility that availability signals are expressed in modality-specific storage sites. In the present study subjects encoded pictures and sounds representing concrete objects. One day later, during fMRI scanning, a verbal cued-recall task was administrated followed by a post-scan recognition task. Items remembered on both tasks were classified as accessible; items not remembered on the first but on the second task were classified as available; and items not remembered on any of the tasks were classified as not available. Multivariate partial-least-squares analyses revealed a modality-independent accessibility network with dominant contributions of left inferior parietal cortex, left inferior frontal cortex, and left hippocampus. Additionally, a modality-specific availability network was identified which included increased activity in visual regions for available pictorial information and in auditory regions for available sound information. These findings show that availability in memory, at least in part, is characterized by systematic changes in brain activity in sensory regions whereas memory access reflects differential activity in a modality-independent, conceptual network, thus indicating qualitative differences between availability and accessibility in memory.
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