| 1. |
- Brehmer, Yvonne, et al.
(författare)
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Neural correlates of training-related working-memory gains in old age
- 2011
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Ingår i: NeuroImage. - : Elsevier BV. - 1053-8119 .- 1095-9572. ; 58:4, s. 1110-1120
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Tidskriftsartikel (refereegranskat)abstract
- Working memory (WM) functioning declines in old age. Due to its impact on many higher-order cognitive functions, investigating whether training can modify WM performance has recently been of great interest. We examined the relationship between behavioral performance and neural activity following five weeks of intensive WM training in 23 healthy older adults (M = 63.7 years). 12 participants received adaptive training (i.e. individually adjusted task difficulty to bring individuals to their performance maximum), whereas the others served as active controls (i.e. fixed low-level practice). Brain activity was measured before and after training, using fMRI, while subjects performed a WM task under two difficulty conditions. Although there were no training-related changes in WM during scanning, neocortical brain activity decreased post training and these decreases were larger in the adaptive training group than in the controls under high WM load. This pattern suggests intervention-related increases in neural efficiency. Further, there were disproportionate gains in the adaptive training group in trained as well as in non-trained (i.e. attention, episodic memory) tasks assessed outside the scanner, indicating the efficacy of the training regimen. Critically, the degree of training-related changes in brain activity (i.e. neocortical decreases and subcortical increases) was related to the maximum gain score achieved during the intervention period. This relationship suggests that the decreased activity, but also specific activity increases, observed were functionally relevant.
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| 2. |
- Brehmer, Yvonne, et al.
(författare)
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Working-memory training in younger and older adults : training gains, transfer, and maintenance
- 2012
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Ingår i: Frontiers in Human Neuroscience. - : Frontiers Media SA. - 1662-5161. ; 6:63, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- Working memory (WM), a key determinant of many higher-order cognitive functions, declines in old age. Current research attempts to develop process-specific WM training procedures, which may lead to general cognitive improvement. Adaptivity of the training as well as the comparison of training gains to performance changes of an active control group are key factors in evaluating the effectiveness of a specific training program. In the present study, 55 younger adults (20–30 years of age) and 45 older adults (60–70 years of age) received 5 weeks of computerized training on various spatial and verbal WM tasks. Half of the sample received adaptive training (i.e., individually adjusted task difficulty), whereas the other half-worked on the same task material but on a low task difficulty level (active controls). Performance was assessed using criterion, near-transfer, and far-transfer tasks before training, after 5 weeks of intervention, as well as after a 3-month follow-up interval. Results indicate that (a) adaptive training generally led to larger training gains than low-level practice, (b) training and transfer gains were somewhat greater for younger than for older adults in some tasks, but comparable across age groups in other tasks, (c) far-transfer was observed to a test on sustained attention and for a self-rating scale on cognitive functioning in daily life for both young and old, and (d) training gains and transfer effects were maintained across the 3-month follow-up interval across age.
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| 3. |
- Westerberg, Lars-Ove, et al.
(författare)
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The development of the ancient irrigation system at Engaruka, northern Tanzania : Physical and societal factors
- 2010
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Ingår i: Geographical Journal. - : Wiley. - 0016-7398 .- 1475-4959. ; 176:4, s. 304-318
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Tidskriftsartikel (refereegranskat)abstract
- Climate data from Empakaai Crater in northern Tanzania, covering the last 1200 years, are related to the establishment, development and decline of the ancient irrigation system at Engaruka. New dates for the system are linked to reconstructed climatic variations and historical data on long-distance and regional trade and migration patterns. A shift from a comparatively humid climate to drier conditions in the 1400s prompted the establishment of irrigated agriculture at Engaruka, and a flourishing long-distance trade increased its value as a water and food source for passing caravans. Once established, the land-use system at Engaruka was sufficiently resilient to survive and even intensify during much drier climate from c. 1500 to 1670 CE (Common Era) and during the decline of caravan trade between c. 1550 and 1750. The ancient land-use system probably reached its maximum extension during the humid conditions between 1670 and 1740, and was deserted in the early to mid 1800s, presumably as a result of the added effects of climate deterioration, the Maasai expansion, and change of livelihood strategies as agriculturalists became pastoralists. Towards the end of the 1800s irrigated agriculture was again established at Engaruka, in part driven by the transfer from pastoral to agricultural livelihoods caused by the Rinderpest.
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| 4. |
- Öberg, Helena, 1974-, et al.
(författare)
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A diatom record of recent environmental change in Lake Duluti, northern Tanzania
- 2012
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Ingår i: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 48:2, s. 401-416
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Tidskriftsartikel (refereegranskat)abstract
- Lake Duluti is a small, topographically closed crater lake located on the flanks of Mt Meru, northern Tanzania. Analyses of diatoms in three short sediment cores and four modern samples from Lake Duluti were used to infer past environmental changes. 210Pb and 137Cs activity profiles combined with AMS 14C dates provide the chronological framework. Weak agreement between the 210Pb and 14C records, together with dating uncertainty, precludes construction of precise age models. The modern diatom flora, from plankton and three periphytic habitats, is dominated by Aulacoseira ambigua (Grunow) Simonsen, Gomphonema parvulum (Kützing) Grunow and Nitzschia amphibia Grunow. All three cores display similar stratigraphic succession, but the relative ratio of habitats represented by the diatoms varies substantially between cores. Diatoms indicate that the oldest part of the record is characterized by relatively low lake level and swampy vegetation. In the late nineteenth or early twentieth century there was a rapid lake level rise and the swamp turned into an open-water lake. High lake levels have prevailed since that time.
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| 5. |
- Öberg, Helena, 1974-
(författare)
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Diatoms in Lake Duluti : Tracking Environmental Variability in Northern Tanzania during the Past 1000 Years
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The tropics are the regions which are least understood climatically and new data on past climate variability is necessary for reliable future modeling of climate change. This thesis contributes with new paleoenvironmental information from a small crater lake in northern Tanzania and provides an additional link between the integrated history of climate, environment and socioeconomic variability in tropical Africa. Pollen and diatom records from three short sediment cores and one piston core have been used to infer variations in past climate and environmental conditions. The chronological framework has been established by 210Pb and 137Cs activity profiles combined with AMS 14C dates on bulk sediment and Bayesian statistics have been used to construct the age-models. Together, the four cores cover approximately the last 1000 years. Modern limnological conditions (temperature, dissolved oxygen, pH and conductivity) and diatom assemblages from plankton, vegetation, stone scrape and near shore sediments have been surveyed to facilitate the paleoenvironmental interpretation. A detailed morphological analysis of Discostella species in Lake Duluti is presented. Frustule morphology of Discostella species have been examined using light microscope (LM) and scanning electron microscope (SEM) and led to the identification of a new variety; Discostella woltereckii v. minor Öberg, Risberg & Stabell. The multi-proxy record from the piston core infers dry conditions c. AD 1040–1470. Between c. AD 1470 and 1510 there are moist conditions with a lake high-stand centered on c. AD 1490. The period c. AD 1510–1640 is dry and between c. AD 1640 and 1790 there are indications of a continuously increase in moisture and higher lake levels, with a brief reversals in the 1660s. The results from the short cores indicate dry conditions from the late 19th century followed by a rapid rise in lake level sometime in the early 20th century. The observed trends show a good correlation with other paleoenvironmental data from East Africa. The results support the general hypothesis of regionally-wide dry conditions in the beginning of the last millennium and an inverse humidity pattern between western equatorial and eastern equatorial sites during the last centuries.
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| 6. |
- Öberg, Helena, et al.
(författare)
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Environmental variability in northern Tanzania from AD 1000 to 1800, as inferred from diatoms and pollen in Lake Duluti
- 2013
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 374, s. 230-241
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Tidskriftsartikel (refereegranskat)abstract
- Fossil pollen and diatoms have been analyzed in a sediment sequence from a topographically closed crater lake in northern Tanzania (Lake Duluti), with the aim to reconstruct past changes in lake level and vegetation dynamics. The results provide a new paleoenvironmental record from equatorial Africa covering the period c. AD 1000 to AD 1800. Overall, the pollen and diatom records generate comparable stories of dry and wet periods. Dry conditions are inferred at c. AD 1040-1470, c. AD 1510-1640 and C. AD 1650-1670 with the lowest lake levels at c. AD 1260-1290 and AD 1600-1640. Wetter conditions occurred c. AD 1640-1650 and c. AD 1670-1790. The chronology is based on combined analyses of Pb-210 activity and AMS C-14 on bulk sediment, and a Bayesian model was applied to establish the age-depth relationship. The hydroclimatic record from Lake Duluti shows good correlation with several East African lakes in a centennial time perspective, although comparison of high frequency variability in the region is hampered by dating uncertainties.
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