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dc.contributor.advisorAslaksen, Per
dc.contributor.authorBystad, Martin Kragnes
dc.date.accessioned2020-11-24T13:27:20Z
dc.date.available2020-11-24T13:27:20Z
dc.date.issued2020-12-18
dc.description.abstract<p>The aim of this thesis was to investigate the effects of transcranial direct current stimulation (tDCS) as a memory enhancer in Alzheimer’s disease patients and healthy individuals. In addition, we wanted to study how verbal memory functions are related to hippocampus subfield volumes. <p>This thesis consists of three reports, in which two of the reports (I and II) aimed to study the effects of tDCS, and the other report (III) focused on verbal memory and subfields of the hippocampus. In all three reports, the California Verbal Learning Test II (CVLT-II) was used to assess verbal memory functions. The CVLT-II is normed for age and sex and is a widely used memory test, in both experimental and clinical settings. <p>In reports I and II, the effect of a stimulation method called “transcranial direct current stimulation (tDCS)” was investigated. This is a noninvasive method in which two or more electrodes are placed on the scalp. The electrode positioning depends on the area intended to be stimulated. A weak direct current is delivered through the scalp and aims to increase cortical excitability (i.e., aims to make the neurons more capable of responding to stimuli). The stimulation electrode (the anode) was placed over the temporal cortex, whereas the reference electrode (the cathode) was placed over the right frontal cortex. <p>In report I, we used a randomized controlled trial design in which 26 patients with Alzheimer’s disease underwent six 30-minute sessions of tDCS stimulation during a two-week period. Half of them received active tDCS stimulation, while the other half received placebo tDCS. We found no significant differences between active and placebo tDCS, neither in the primary outcome nor in the secondary outcome measures. <p>In report II, 40 healthy participants underwent six tDCS sessions for two consecutive days. Half of the participants received active tDCS, and the other half received placebo tDCS. No significant differences were found in verbal memory outcomes. However, in the young participants there was a significant difference between active and placebo tDCS in executive functions measured by the Trail Making Test, part B (TMT B). <p>In report II, we investigated the relation between verbal memory and hippocampal subfield volumes in 47 right-handed healthy adults. T1-weighted MRI results were obtained using a 1,5 Tesla scanner. The results showed a significant correlation between left hippocampal subfields volumes and verbal memory. However, no significant correlations were found between right hippocampal volumes and verbal memory. <p>The overall conclusions are as follows: 1) In patients with Alzheimer’s disease, six 30-minute sessions of active tDCS over a period of two weeks did not offer any significant improvements in memory functions, compared to the placebo tDCS results. However, the generalizability is limited due to the small sample size. 2) In healthy participants, six 30-minute sessions of active tDCS for two consecutive days did not offer significantly better memory outcomes, compared to the placebo tDCS results. 3) In healthy adults, there was a significant correlation between verbal memory performance and left hippocampal subfield volume.en_US
dc.description.abstractHensikten med denne avhandlingen var å undersøke om transcranial Direct Current Stimulation (tDCS) kan bedre verbale hukommelsesfunksjoner hos pasienter med Alzheimers sykdom og friske deltakere, samt å undersøke sammenhengen mellom verbal hukommelse og volum av hippocampus og sub-strukturer i hippocampus. Avhandingen består at tre artikler, der to av artiklene (1 og 2) undersøkte effektene av tDCS, mens den siste artikkelen (3) studerte verbal hukommelse og hippocampus volum. I alle tre artiklene ble California Verbal Learning Test II (CVLT-II) brukt som mål på verbal hukommelsesfunksjon. CVLT-II er en nevropsykologisk test som er normert for bade alder og kjønn og er mye brukt i forskning og klinikk. I artikkel 1 og 2 ble effekten av transkraniell likestrømsstimulering (tDCS) undersøkt. Dette er en ikke-invasiv metode der to eller flere elektroder plasseres i hodebunnen, over det området man ønsker å stimulere. En svak likestrøm går gjennom hodeskallen og har til hensikt å påvirke kortikal eksitabilitet (dvs. at nevronene reagerer lettere på stimuli). Stimuleringselektroden (anoden) ble plassert over venstre temporal korteks, mens referanse elektroden (katoden) ble plassert over høyre frontal korteks. I artikkel 1 brukte vi et randomisert kontrollert design der 26 pasienter med Alzheimers sykdom fikk seks behandlingssesjoner med tDCS i løpet av to uker. Varigheten på hver sesjon var 30 minutter. Halvparten av pasientene fikk aktiv tDCS, mens den andre halvparten fikk placebo tDCS. Vi fant ingen signifikant forskjell mellom aktiv og placebo tDCS, hverken på primære eller sekundære utfallsmål. I artikkel 2 fikk 40 friske deltakere seks sesjoner med tDCS, fordelt på to påfølgende dager. Halvparten av dem fikk aktiv tDCS, men den andre halvparten fikk placebo tDCS. Det ble ikke funnet noen signifikant forskjell i verbal hukommelsesfunksjon, men det var en signifikant forskjell mellom aktiv og placebo tDCS i eksekutiv funksjon, målt med Trail Making Test B (TMT-B). I artikkel 3 undersøkte vi sammenhengen mellom verbal hukommelsesfunksjon og hippocampus volum hos 47 høyrehendte voksne deltakere. En MR scanner med 1,5 tesla ble benyttet. Resultatene viste en signifikant korrelasjon mellom venstre hippocampus volum og verbal hukommelse, mens det derimot ikke var noen signifikant korrelasjon mellom høyre hippocampus volume og verbal hukommelse. Konklusjonene fra de tre rapportene var følgende: 1) Hos pasienter med Alzheimers sykdom gir ikke seks 30 minutters seksjoner med aktiv tDCS i løpet av to uker noen signifikant forbedring i hukommelsesfunksjon, sammenliknet med placebo tDCS. Det er imidlertid få deltakere, noe om begrenser generaliserbarheten 2) Hos friske deltakere ga ikke seks sesjoner med 30 minutter aktiv tDCS over to påfølgende dager noen signifikant forbedring i hukommelsen, sammenliknet med placebo tDCS. 3) Hos friske deltakerne var det en signifikant korrelasjon mellom verbal hukommelse og venstre hippocampus volum.en_US
dc.description.doctoraltypeph.d.en_US
dc.description.popularabstractThe aim of this thesis was to investigate the effect of transcranial Direct Current Stimulation (tDCS) as a memory enhancer in Alzheimer`s disease and healthy individuals. We used California Verbal Learning Test II (CVLT-II) to assess memory functions. This is a widely used memory test. By using this memory test (CVLT-II), we wanted to investigate if a stimulation method called “transcranial Direct Current Stimulation (tDCS)” could improve memory. tDCS is a simple method where two or more electrodes are placed on the scalp. The electrode positioning depends on the area aimed to be stimulated. A weak direct current is delivered through the scalp and aims to increase activity. This is very safe and not uncomfortable. Both healthy participants and patients with Alzheimer`s disease recieved such stimulation. We used memory tests (CVLT-II) before and after the stimulation, to study if the tDCS stimulaiton improved memory. We failed to find that tDCS could improve memory.en_US
dc.identifier.urihttps://hdl.handle.net/10037/19913
dc.language.isoengen_US
dc.publisherUiT The Arctic University of Norwayen_US
dc.publisherUiT Norges arktiske universiteten_US
dc.relation.haspart<p>Paper I: Bystad, M., Grønli, O., Rasmussen, I.D., Gundersen, N., Nordvang, L., Wang-Iversen, H. & Aslaksen, P.M. (2016). Transcranial direct current stimulation as a memory enhancer in patients with Alzheimer`s disease: A randomized placebo controlled trial. <i>Alzheimer`s Research & Therapy, 8</i>, 13. Also available in Munin at <a href=https://hdl.handle.net/10037/10502>https://hdl.handle.net/10037/10502</a>. <p>Paper II: Bystad, M., Storø, B., Gundersen, N., Wiik, I.L., Nordvang, L., Grønli, O., Daae-Rasmussen, Aslaksen, P.M. Can accelerated transcranial Direct Current Stimulation improve memory functions? An experimental, placebo-controlled study. (Submitted manuscript). <p>Paper III: Aslaksen, P.M., Bystad, M., Ørbo, M.C. & Vangberg, T.R. (2018). The relation of hippocampal subfield volumes to verbal episodic memory measured by California Verbal Learning Test II in healthy adults. <i>Behavioral Brain Research, 351</i>, 131-137. Also available at <a href=https://doi.org/10.1016/j.bbr.2018.06.008>https://doi.org/10.1016/j.bbr.2018.06.008</a>. Accepted manuscript version available in Munin at <a href=https://hdl.handle.net/10037/13974>https://hdl.handle.net/10037/13974</a>.en_US
dc.rights.accessRightsopenAccessen_US
dc.rights.holderCopyright 2020 The Author(s)
dc.rights.urihttps://creativecommons.org/licenses/by-nc-sa/4.0en_US
dc.rightsAttribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0)en_US
dc.subjectPsykologien_US
dc.subjectVDP::Social science: 200::Psychology: 260en_US
dc.subjectVDP::Samfunnsvitenskap: 200::Psykologi: 260en_US
dc.titleTranscranial Direct Current Stimulation as a memory enhancer in healthy participants and patients with Alzheimer`s diseaseen_US
dc.typeDoctoral thesisen_US
dc.typeDoktorgradsavhandlingen_US


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