| 1. |
- Habich, Annegret, et al.
(författare)
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Stimulating aged brain with transcranial direct current stimulation : Opportunities and challenges
- 2020
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Ingår i: Psychiatry Research. - : Elsevier. - 0925-4927 .- 1872-7506. ; 306
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Tidskriftsartikel (refereegranskat)abstract
- Ageing involves significant neurophysiological changes that are both systematic while at the same time exhibiting divergent trajectories across individuals. These changes underlie cognitive impairments in elderly while also affecting the response of aged brains to interventions like transcranial direct current stimulation (tDCS). While the cognitive benefits of tDCS are more variable in elderly, older adults also respond differently to stimulation protocols compared to young adults. The age-related neurophysiological changes influencing the responsiveness to tDCS remain to be addressed in-depth. We review and discuss the premise that, in comparison to the better calibrated brain networks present in young adults, aged systems perform further away from a homoeostatic set-point. We argue that this age-related neurophysiological deviation from the homoeostatic optimum extends the leeway for tDCS to modulate the aged brain. This promotes the potency of immediate tDCS effects to induce directional plastic changes towards the homoeostatic equilibrium despite the impaired plasticity induction in elderly. We also consider how age-related neurophysiological changes pose specific challenges for tDCS that necessitate proper adaptations of stimulation protocols. Appreciating the distinctive properties of aged brains and the accompanying adjustment of stimulation parameters can increase the potency and reliability of tDCS as a treatment avenue in older adults.
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| 2. |
- Melin, Jeanette, et al.
(författare)
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Forward and Backward Recalling Sequences in Spatial and Verbal Memory Tasks : What Do We Measure?
- 2023
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Ingår i: Entropy. - : MDPI. - 1099-4300. ; 25:5
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Tidskriftsartikel (refereegranskat)abstract
- There are different views in the literature about the number and inter-relationships of cognitive domains (such as memory and executive function) and a lack of understanding of the cognitive processes underlying these domains. In previous publications, we demonstrated a methodology for formulating and testing cognitive constructs for visuo-spatial and verbal recall tasks, particularly for working memory task difficulty where entropy is found to play a major role. In the present paper, we applied those insights to a new set of such memory tasks, namely, backward recalling block tapping and digit sequences. Once again, we saw clear and strong entropy-based construct specification equations (CSEs) for task difficulty. In fact, the entropy contributions in the CSEs for the different tasks were of similar magnitudes (within the measurement uncertainties), which may indicate a shared factor in what is being measured with both forward and backward sequences, as well as visuo-spatial and verbal memory recalling tasks more generally. On the other hand, the analyses of dimensionality and the larger measurement uncertainties in the CSEs for the backward sequences suggest that caution is needed when attempting to unify a single unidimensional construct based on forward and backward sequences with visuo-spatial and verbal memory tasks.
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| 3. |
- Melin, Jeanette, et al.
(författare)
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NeuroMET Memory Metric : Improving accuracy and comparability with crosswalks
- 2023
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Ingår i: Alzheimer’s & Dementia. - 2352-8737. ; 19:S4
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Tidskriftsartikel (refereegranskat)abstract
- Background: The ability to measure, track over time, and compare memory ability for people with neurodegeneration is important. However, currently, full comparability of memory test data is limited by a lack of quality assurance of memory measurements. At AAIC 2021, we presented a preliminary item bank to assess memory, composed by selecting items from legacy tests according to metrological principles through use of the Rasch model and with item equivalence based on entropy. Method: Here, we demonstrate direct comparability of measurements generated from different tests, with the new NeuroMET Memory Metric comprising 87 selected items for task difficulty from: the Corsi Block Test, Digit Span Test, Rey’s Auditory Verbal Learning Test, Word Learning List from the CERAD test battery and the Mini Mental State Examination. Data were collected from the European EMPIR NeuroMET and the SmartAge studies recruited at Charité Hospital (Healthy controls n = 92; Subjective cognitive decline n = 160; Mild Cognitive Impairment n = 50; and Alzheimer’s Disease n = 58; age range 55-87). Results: The Rasch analysis showed well-targeted items for all participants’ abilities; good fit to the measurement model, with 83 items (95%) having fit residuals within the expected range and satisfactory unidimensionality, and item reliability of 0.96. The full item bank comprising 87 short-term memory items gave a person reliability of 0.85. Subsequently, a conversion table was created linking the raw scores from the legacy tests to the common NeuroMET Memory Metric and to individual legacy tests. Conclusion: Legacy memory tests have previously proven useful in clinical practice and research, and will continue to be used, but have to date been metrologically limited. The provided conversion table, linking these legacy memory tests to a metrologically assured scale, viz., the NeuroMET memory metric, remedies this deficiency. The NeuroMET memory metric will be included in the first ever prototype of a metrological validated app used to deliver memory tests. Clinicians and researchers will be able to select sets of items to produce data, via a scoring algorithm for transforming patient responses to measures, in a common frame of reference.
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| 4. |
- Melin, Jeanette, et al.
(författare)
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The Role of Entropy in Construct Specification Equations (CSE) to Improve the Validity of Memory Tests : Extension to Word Lists
- 2022
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Ingår i: Entropy. - : MDPI. - 1099-4300. ; 24:7
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Tidskriftsartikel (refereegranskat)abstract
- Metrological methods for word learning list tests can be developed with an information theoretical approach extending earlier simple syntax studies. A classic Brillouin entropy expression is applied to the analysis of the Rey’s Auditory Verbal Learning Test RAVLT (immediate recall), where more ordered tasks—with less entropy—are easier to perform. The findings from three case studies are described, including 225 assessments of the NeuroMET2 cohort of persons spanning a cognitive spectrum from healthy older adults to patients with dementia. In the first study, ordinality in the raw scores is compensated for, and item and person attributes are separated with the Rasch model. In the second, the RAVLT IR task difficulty, including serial position effects (SPE), particularly Primacy and Recency, is adequately explained (Pearson’s correlation = 0.80) with construct specification equations (CSE). The third study suggests multidimensionality is introduced by SPE, as revealed through goodness-of-fit statistics of the Rasch analyses. Loading factors common to two kinds of principal component analyses (PCA) for CSE formulation and goodness-of-fit logistic regressions are identified. More consistent ways of defining and analysing memory task difficulties, including SPE, can maintain the unique metrological properties of the Rasch model and improve the estimates and understanding of a person’s memory abilities on the path towards better-targeted and more fit-for-purpose diagnostics. © 2022 by the authors.
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