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Computational modeling of the neural mechanisms underlying working memory
Linköping University, Department of Physics, Chemistry and Biology, Computational Biology. Linköping University, The Institute of Technology.
2005 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The performance on various cognitive tasks, from language to selective attention and guiding future actions depends on working memory (WM), the capacity to hold and manipulate limited items of information. However, neural basis of WM and the capacity limitation are still unclear. The present work includes behavioral, functional magnetic resonance imaging (fMRI) and computational modeling studies of the visuospatial WM in order to identify the neural correlates of WM capacity. In the first study we used behavioral distracting stimuli in order to identify cellular mechanisms that accounts for the observed behavioral decrease in mnemonic accuracy as a function of distractor distance. The study provided theoretical support that independently of the cellular and synaptic properties, increased neuronal firing rates accounted for higher mnemonic accuracy and resistance against distractors. In the second study we performed fMRI experiments on adults and children to monitor brain activity during a WM task. We isolated the delay-related activity and analyzed group differences and the distractor influence both behaviorally and in terms of changed brain activity. The fMRJ study showed higher brain activity in inferior frontal and intraparietal cortex in adults compared to children during the delay periods of WM tasks. Furthermore, adults were more accurate and less distractible than children. In a subsequent study we addressed the cellular changes during WM development. The study combined a computational analysis with fMRl in order to establish putative maturational processes governing developmental changes in brain activity. We found that the increase in activit' together with higher resistance against distractors could be explained by computational models having stronger connectivity between network areas. Our studies suggest that increased firing rates of the cortical areas involved in the maintenance of visuospatial information accounts for the developmental related increase of activity in areas associated with WM processes as well as for the higher resistance against distractors. Therefore, increasing the neural activity of the WM circuitry using either psychophysiological training protocols or pharmacological manipulation may have a beneficial effect on the WM capacity and distractibility.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet , 2005. , 34 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1196
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-29963Local ID: 15390ISBN: 91-85457-29-9 (print)OAI: oai:DiVA.org:liu-29963DiVA: diva2:250782
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2013-11-27
List of papers
1. Neuronal firing rates account for distractor effects on mnemonic accuracy in a visuo-spatial working memory task
Open this publication in new window or tab >>Neuronal firing rates account for distractor effects on mnemonic accuracy in a visuo-spatial working memory task
2007 (English)In: Biological Cybernetics, ISSN 0340-1200, E-ISSN 1432-0770, Vol. 96, no 4, 407-419 p.Article in journal (Refereed) Published
Abstract [en]

Persistent neural activity constitutes one neuronal correlate of working memory, the ability to hold and manipulate information across time, a prerequisite for cognition. Yet, the underlying neuronal mechanisms are still elusive. Here, we design a visuo- spatial delayed-response task to identify the relationship between the cue-distractor spatial distance and mnemonic accuracy. Using a shared experimental and computational test protocol, we probe human subjects in computer experiments, and subsequently we evaluate different neural mechanisms underlying persistent activity using an in silico prefrontal network model. Five modes of action of the network were tested: weak or strong synaptic interactions, wide synaptic arborization, cellular bistability and reduced synaptic NMDA component. The five neural mechanisms and the human behavioral data, all exhibited a significant deterioration of the mnemonic accuracy with decreased spatial distance between the distractor and the cue. A subsequent computational analysis revealed that the firing rate and not the neural mechanism per se, accounted for the positive correlation between mnemonic accuracy and spatial distance. Moreover, the computational modeling predicts an inverse correlation between accuracy and distractibility. In conclusion, any pharmacological modulation, pathological condition or memory training paradigm targeting the underlying neural circuitry and altering the net population firing rate during the delay is predicted to determine the amount of influence of a visual distraction.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-38402 (URN)10.1007/s00422-006-0139-8 (DOI)000245292700004 ()44188 (Local ID)44188 (Archive number)44188 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2013-11-27
2. Brain activity related to working memory and distraction in children and adults
Open this publication in new window or tab >>Brain activity related to working memory and distraction in children and adults
2007 (English)In: Cerebral Cortex, ISSN 1047-3211, E-ISSN 1460-2199, Vol. 17, no 5, 1047-1054 p.Article in journal (Refereed) Published
Abstract [en]

In order to retain information in working memory (WM) during a delay, distracting stimuli must be ignored. This important ability improves during childhood, but the neural basis for this development is not known. We measured brain activity with functional magnetic resonance imaging in adults and 13-year-old children. Data were analyzed with an event-related design to isolate activity during cue, delay, distraction, and response selection. Adults were more accurate and less distractible than children. Activity in the middle frontal gyrus and intraparietal cortex was stronger in adults than in children during the delay, when information was maintained in WM. Distraction during the delay evoked activation in parietal and occipital cortices in both adults and children. However, distraction activated frontal cortex only in children. The larger frontal activation in response to distracters presented during the delay may explain why children are more susceptible to interfering stimuli.

Keyword
Development, Dorsolateral, Event related, fMRI, Prefrontal, Visuospatial
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-47966 (URN)10.1093/cercor/bhl014 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2013-11-27
3. Stronger fronto-parietal connectivity accounts for development of working memory-related brain activity
Open this publication in new window or tab >>Stronger fronto-parietal connectivity accounts for development of working memory-related brain activity
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Cognitive functions, including working memory capacity, improve during childhood and early adulthood. Several maturational processes take place during that time, most importantly the myelination of axons, pruning of synapses and strengthening of the remaining synapses. However, it has not yet been shown how to directly relate these cellular changes to working memory development and associated changes in brain activity. Here, we bridge this gap by integrating biophysically-based computational modelling and functional MRI of the visuospatial working memory. Cellular mechanisms corresponding to different maturational processes were implemented in in silico 'child' networks, and the predicted difference in activity between 'child' and a reference 'adult' network was then compared to measured brain activity in children and adults. Network models with stronger connectivity between brain areas, but not networks with faster conduction or increased neuronal specificity, were supported by measured developmental increases in brain activity and correlations between frontal and parietal areas. The 'adult' networks with stronger fronto-parietal connections also exhibited greater stability during distraction, which was consistent with the developmental improvement in working memory performance.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-102032 (URN)
Available from: 2013-11-27 Created: 2013-11-27 Last updated: 2013-11-27

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