9 results on '"Plessis, Lindie"'
Search Results
2. An In Vivo 1H Magnetic Resonance Spectroscopy Study of the Deep Cerebellar Nuclei in Children with Fetal Alcohol Spectrum Disorders
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du Plessis, Lindie, Jacobson, Joseph L., Jacobson, Sandra W., Hess, Aaron T., van der Kouwe, Andre, Avison, Malcolm J., Molteno, Christopher D., Stanton, Mark E., Stanley, Jeffrey A., Peterson, Bradley S., and Meintjes, Ernesta M.
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- 2014
- Full Text
- View/download PDF
3. Game Farm and Hunting Tourism
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van der Merwe, Peet, du Plessis, Lindie, van der Merwe, Peet, and du Plessis, Lindie
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- 2014
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4. An investigation of the integrity of two components of the cerebellar neurocircuitry involved in classical eyeblink conditioning in children prenatally exposed to alcohol: a magnetic resonance spectroscopy and functional magnetic resonance imaging study
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Du Plessis, Lindie and Meintjes, Ernesta
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InformationSystems_INFORMATIONSTORAGEANDRETRIEVAL ,ComputingMethodologies_DOCUMENTANDTEXTPROCESSING ,Biomedical Engineering ,GeneralLiterature_REFERENCE(e.g.,dictionaries,encyclopedias,glossaries) - Abstract
Includes bibliographical references., Impairment in classical eyeblink conditioning (EBC) has previously been reported in children with fetal alcohol spectrum disorders (FASD) (Jacobson et al., 2008). The deep cerebellar nuclei and cerebellar cortex are critical elements of the cerebellar-brainstem circuitry that mediates EBC (Green et al., 2002a; Yeo and Hardiman, 1992; Perret et al., 1993). In this study, we used magnetic resonance spectroscopy (MRS) and functional MRI (fMRI) to assess the effects of prenatal alcohol exposure on brain metabolism in the cerebellar deep nuclei and brain function in the cerebellar cortex, respectively. We found that higher levels of prenatal alcohol exposure were associated with lower levels of both N-Acetylaspartate (NAA) and choline-containing metabolites, and with higher levels of glutamate plus glutamine (Glx), suggesting a disruption of the glutamate-glutamine cycling involved in glutamatergic excitatory neurotransmission. Since the interpositus nucleus is one of the most crucial structures in the acquisition of the EBC response, abnormal metabolism in this region could be responsible for altered synaptic plasticity in children with FASD. Of the four cerebellar regions that were identified as being activated more by control children during rhythmic vs. non-rhythmic finger tapping, smaller differences in BOLD (blood oxygenation level dependent) activation were observed in children with FASD in two, namely vermis IV-V and right Crus I. Increasing levels of prenatal alcohol exposure were, however, associated with smaller differences in activation in all four regions, all of which have previously been linked to timed responses. In the paced/unpaced finger tapping fMRI study, we found four regions where increased BOLD activation during unpaced tapping compared to rest was associated with improved ability to maintain rhythm as evidenced by lower intertapping variability - right VIIIa and b, left VIIIa and right VI. These regions have previously been implicated in motor control with additional evidence of timing in lobule VI. In three of the regions, all except right VIIIa, increasing alcohol exposure was related to smaller increases in activation during unpaced tapping, with the strongest relations seen in the dosage dependent variable. Interestingly, the location of the activation in right VI is similar to a region that has been implicated in studies of EBC (Blaxton et al., 1996; Cheng et al., 2008). Our results point to altered metabolic levels in the deep nuclei and reduced functioning of several cerebellar cortical regions in children with FASD, highlighting the extensive damage caused by prenatal alcohol exposure. Although we did not find associations of EBC performance with either metabolite levels or activity in these regions, suggesting that damage to these areas are not primarily responsible for the observed EBC deficit, the extent of this damage could play a role in the impaired EBC performance seen in these children.
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- 2014
5. Magnetic resonance spectroscopy quality assessment at CUBIC and application to the study of the cerebellar deep nuclei in children with fetal alcohol spectrum disorder
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Du Plessis, Lindie and Meintjies, Ernesta
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Human Biology ,myo-inositol ,magnetic resonance imaging ,phantom ,fetal alcohol spectrum disorder ,magnetic resonance spectroscopy ,metabolites - Abstract
Includes bibliographical references (leaves 73-79)., In vivo magnetic resonance spectroscopy (MRS) is an imaging technique that allows the chemical study of human tissue non-invasively. The method holds great promise as a diagnostic tool once its reliability has been established. Inter-scanner variability has, however, hampered this from happening as results cannot easily be compared if acquired on different scanners. In this study a phantom was constructed to determine the localisation efficiency of the 3 T Siemens Allegra MRI scanner located at the Cape Universities Brain Imaging Centre (CUBIC). Sufficient localisation is the key to acquiring useful spectroscopic data as only the signal from a small volume of interest (VOI) is typically acquired. The phantom consisted of a Perspex cube located inside a larger Perspex sphere. Solutions of the cerebral metabolites N-acetyl aspartate (NAA) and choline (Cho) were placed in the inner cube and outer sphere respectively. The phantom was scanned at a range of voxel sizes and echo times in order to determine parameters that typically indicate the performance of the scanner in question. The resultant full width at half maximum (FWHM) and signal to noise ratio (SNR) values indicated that optimal results were obtained for a voxel with dimensions 20 x 20 x 20 mm3. The selection efficiency could not be measured due to limitations in the scanner, but two other performance parameters ' extra volume suppression (EVS) and contamination ' could be determined. The EVS showed that the scanner was able to eliminate the entire background signal from the out-of-voxel region when voxel sizes with dimensions (20 mm)3 and (30 mm)3 were used. This performance decreased to 96.2% for a voxel size of (50 mm)3. The contamination indicated that the unwanted signal, weighted by the respective proton densities of the chemicals, ranged from 12% in the (20 mm)3 voxel to 24% in the (50 mm)3 voxel. These ranges are well within acceptable limits for proton MRS. Analysis of the water suppression achieved in the scanner showed an efficiency of 98.84%, which is acceptable for proton spectroscopy. It was also found that manual iv shimming of the scanner improved the spectra obtained, as compared to the automated shimming performed by the scanner. The second objective of the study was to quantify absolute metabolite concentrations in the familiar SI units of mM as results were previously mostly expressed as metabolite ratios. The LCModel software was used to assess two methods of determining absolute metabolite concentrations and the procedure using water scaling consistently showed superior performance to a method using a calibration factor. The method employing water scaling was then applied to a study of fetal alcohol spectrum disorder (FASD) where the deep cerebellar nuclei of children with FASD and a control group were scanned. The cerebellar nuclei were of interest as children with FASD show a remarkably consistent deficit in eye blink conditioning (EBC). The cerebellar deep nuclei is known to play a critical role in the EBC response. The results show significant decreases in the myo-inositol (mI) and total choline (tCho) concentrations of children with FASD in the deep cerebellar nuclei compared to control children. The FAS/PFAS subjects have a mean mI concentration of 4.6 mM as compared to a mean of 5.3 mM in the controls. A Pearson correlation showed that there was a significant relationship between decreasing mI concentrations with increasing prenatal alcohol exposure. The mean tCho concentrations are 1.3 mM for FAS/PFAS and 1.5 mM for the controls. There was no significant differences between the heavily exposed group and either the FAS/PFAS or the control subjects for either metabolite. The decreased mI and tCho concentrations may indicate deficient calcium signalling or decreased cell membrane integrity ' both of which can explain the compromised cerebellar learning in FASD subjects.
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- 2010
6. An In Vivo 1H Magnetic Resonance Spectroscopy Study of the Deep Cerebellar Nuclei in Children with Fetal Alcohol Spectrum Disorders.
- Author
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Plessis, Lindie, Jacobson, Joseph L., Jacobson, Sandra W., Hess, Aaron T., Kouwe, Andre, Avison, Malcolm J., Molteno, Christopher D., Stanton, Mark E., Stanley, Jeffrey A., Peterson, Bradley S., and Meintjes, Ernesta M.
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NUCLEAR magnetic resonance spectroscopy , *BRAIN physiology , *FETAL alcohol syndrome , *ASPARTIC acid , *CHOLINE , *INTELLIGENCE tests , *RESEARCH funding , *MULTIPLE regression analysis , *DATA analysis software , *PRENATAL exposure delayed effects - Abstract
Background Prenatal alcohol exposure has been linked to impairment in cerebellar structure and function, including eyeblink conditioning. The deep cerebellar nuclei, which play a critical role in cerebellar-mediated learning, receive extensive inputs from brain stem and cerebellar cortex and provide the point of origin for most of the output fibers to other regions of the brain. We used in vivo 1H magnetic resonance spectroscopy ( MRS) to examine effects of prenatal alcohol exposure on neurochemistry in this important cerebellar region. Methods MRS data from the deep cerebellar nuclei were acquired from 37 children with heavy prenatal alcohol exposure and 17 non- or minimally exposed controls from the Cape Coloured (mixed ancestry) community in Cape Town, South Africa. Results Increased maternal alcohol consumption around time of conception was associated with lower N-Acetylaspartate ( NAA) levels in the deep nuclei ( r = −0.33, p < 0.05). Higher levels of alcohol consumption during pregnancy were related to lower levels of the choline-containing metabolites ( r = −0.37, p < 0.01), glycerophosphocholine plus phosphocholine (Cho). Alcohol consumption levels both at conception ( r = 0.35, p < 0.01) and during pregnancy ( r = 0.38, p < 0.01) were related to higher levels of glutamate plus glutamine (Glx). All these effects continued to be significant after controlling for potential confounders. Conclusions The lower NAA levels seen in relation to prenatal alcohol exposure may reflect impaired neuronal integrity in the deep cerebellar nuclei. Our finding of lower Cho points to disrupted Cho metabolism of membrane phospholipids, reflecting altered neuropil development with potentially reduced content of dendrites and synapses. The alcohol-related alterations in Glx may suggest a disruption of the glutamate-glutamine cycling involved in glutamatergic excitatory neurotransmission. [ABSTRACT FROM AUTHOR]
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- 2014
- Full Text
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7. THE INFLUENCE OF DEMOGRAPHIC FACTORS ON TRAVEL BEHAVIOUR OF VISITORS TO NATURE-BASED PRODUCTS IN SOUTH AFRICA.
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Slabbert, Elmarie and Du Plessis, Lindie
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TOURIST attitudes ,MARKETING strategy ,TOURISM marketing ,SUSTAINABLE development ,NATIONAL parks & reserves - Abstract
Nature-based products in South Africa are playing an increasingly important role in attracting visitors to the country. It thus becomes more important to understand the travel behaviour of visitors as this can influence future development and marketing strategies to these products. However information in this regard is lacking which creates challenges in the sustainable development of nature-based products. It is therefore the aim of this paper to determine the influence of demographic factors on travel behaviour of visitors to nature-based products in South Africa. A survey was done in 2010 which included nine National Parks in South Africa resulting in 1300 questionnaires. A factor analysis on travel motivations revealed five factors with the highest mean value obtained for 'relaxation'. A second factor analysis for park experiences also revealed five factors with the highest mean value obtained for 'activities and facilities. A t-test for Equality of Means was calculated for age, home language, presence of children and province, and revealed significant differences on both travel motivations and park experiences. Most differences exist on Relaxation and Learning for travel motivations and Maintenance for park experiences. An ANOVA was done on qualification and travel motivations and park preferences and revealed only one significant difference. [ABSTRACT FROM AUTHOR]
- Published
- 2011
8. Comparison of resting state functional networks in HIV infected and uninfected children at age 9 years
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Stoltsz, Werner Heinrich, Meintjes, Ernesta M, and du Plessis, Lindie
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Biomedicine ,Biomedical Engineering - Abstract
Over 2.5 million children are infected with HIV, the majority of whom reside in Sub-Saharan Africa. Treatment coverage is steadily gaining momentum, reducing mortality and morbidity. Yet little is known about brain development in HIV-infected (HIV+) children who are on highly-active antiretroviral therapy (ART), with viral load suppression from a young age. Here, we use resting state fMRI (rs-fMRI) to examine the impact of HIV and ART on the development of functional networks in 9-year-old vertically HIV-infected children compared to age-matched controls of similar socioeconomic status. We present analyses for a sample of 40 HIV+ (9.2 ± 0.20 years; 16 males) children from the Children with HIV Early Antiretroviral (CHER) clinical trial (Cotton et al. 2013; Violari et al. 2008) and 24 uninfected (12 exposed; 12 males; 9.6 ± 0.52 years) controls from an interlinking vaccine trial (Madhi et al. 2010). Scans were performed at the Cape Universities Body Imaging Centre (CUBIC) in Cape Town, South Africa. We investigated HIV-related differences in within- and between-network functional connectivity (FC) using independent component analysis(ICA) and seed-based correlation analysis (SCA). For SCA, seeds were placed in the structural core, in regions implicated in HIV-related between-group differences at age 7 years, and in regions associated with neuropsychological domains impaired in our cohort. In addition, we evaluated associations of past and present immune health measures with within-network connectivity using ICA. We found no HIV-related intra-network FC differences within any ICA-generated RSNs at age 9 years, perhaps as a result of within-network connectivity not being sufficiently robust at this age. We found a positive association of CD4%, both current and in infancy, with functional integration of left lobule 7 into the cerebellum network at age 9 years. Long-term impact of early immune health supports recently-revised policies of commencing ART immediately in HIV+ neonates. ii Compared to uninfected children, HIV+ children had increased FC to several seeds. Firstly, to seeds associated with the planning and visual perception neuropsychological domains. Secondly, to structural core seeds in the extrastriate visual cortex (of the medial visual network) and the right angular gyrus (of the temporoparietal network). Finally, to left paracentral (somatosensory network) and right precuneus (posterior DMN) seeds previously revealing between-group differences at age 7 years. The connections with greater FC in HIV+ children may variously indicate functional recruitment of additional brain capacity, immature excess of short-range connections, and/or immature excess of between-network connections. In conclusion, despite early ART and early virologic suppression, HIV+ children demonstrate instances of abnormal FC at age 9 years. Disruption to visual cortex is marked, consistent with indications from neuropsychological testing that visual perception is disrupted. The profile of HIV- and/or ART-related effects on FC differs considerably between the two ages of 7 and 9 years, but both show characteristics of immature functional organisation compared with age-matched controls.
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- 2018
9. Neural correlates of cerebellar-mediated timing during finger tapping in children with fetal alcohol spectrum disorders.
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du Plessis L, Jacobson SW, Molteno CD, Robertson FC, Peterson BS, Jacobson JL, and Meintjes EM
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- Child, Female, Fingers, Humans, Image Interpretation, Computer-Assisted, Magnetic Resonance Imaging, Male, Cerebellum physiopathology, Fetal Alcohol Spectrum Disorders physiopathology, Psychomotor Performance physiology
- Abstract
Objectives: Classical eyeblink conditioning (EBC), an elemental form of learning, is among the most sensitive indicators of fetal alcohol spectrum disorders. The cerebellum plays a key role in maintaining timed movements with millisecond accuracy required for EBC. Functional MRI (fMRI) was used to identify cerebellar regions that mediate timing in healthy controls and the degree to which these areas are also recruited in children with prenatal alcohol exposure., Experimental Design: fMRI data were acquired during an auditory rhythmic/non-rhythmic finger tapping task. We present results for 17 children with fetal alcohol syndrome (FAS) or partial FAS, 17 heavily exposed (HE) nonsyndromal children and 16 non- or minimally exposed controls., Principal Observations: Controls showed greater cerebellar blood oxygen level dependent (BOLD) activation in right crus I, vermis IV-VI, and right lobule VI during rhythmic than non-rhythmic finger tapping. The alcohol-exposed children showed smaller activation increases during rhythmic tapping in right crus I than the control children and the most severely affected children with either FAS or PFAS showed smaller increases in vermis IV-V. Higher levels of maternal alcohol intake per occasion during pregnancy were associated with reduced activation increases during rhythmic tapping in all four regions associated with rhythmic tapping in controls., Conclusions: The four cerebellar areas activated by the controls more during rhythmic than non-rhythmic tapping have been implicated in the production of timed responses in several previous studies. These data provide evidence linking binge-like drinking during pregnancy to poorer function in cerebellar regions involved in timing and somatosensory processing needed for complex tasks requiring precise timing.
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- 2014
- Full Text
- View/download PDF
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