Doctoral Degrees (Psychiatry)

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Browsing Doctoral Degrees (Psychiatry) by Author "Du Plessis, Stefan"

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    Measuring the impact of HIV on the fronto-striatal system
    (Stellenbosch : Stellenbosch University, 2016-12) Du Plessis, Stefan; Emsley, Robin Alexander; Vink, Matthijs; Stellenbosch University. Faculty of Medicine and Health Science. Dept. of Psychiatry.
    ENGLISH SUMMARY : HIV infection remains a major contributor to the global health burden despite the introduction of effective prevention strategies and the effectiveness of combined antiretroviral therapy (cART). Of particular importance is the impact of HIV on the brain. While cART has been successful in treating the more severe forms HIV induced cognitive impairment, the minor forms of impairment are now more prevalent. There remains some controversy with regard to the latter. Being diagnosed in the absence of other symptoms, there is some doubt that this category of cognitive impairment is valid at all. As such, investigating HIV induced functional brain changes may be helpful in the study of these forms of impairment. Although functional magnetic resonance imaging (fMRI) studies have thus far shown various forms of functional impairment in the brain, how these impairments relate to one another is unclear. Many key aspects of HIV’s potential impact on the frontostriatal system remain unexplored. Our overall objective was therefore to investigate the early impact of HIV on the brain using fMRI as an objective measurement tool. First, we investigated the effects of HIV on the brain by performing a quantitative meta analysis of all suitable fMRI data. Next, we proceeded to investigate the fronto-striatal network based on the results of the meta-analysis by performing fMRI imaging in a sample of HIV+ participants and matched HIV negative controls. Participants performed a stop-signal anticipation and a monetary incentive delay task to investigate the impact of HIV on important sub-networks of the fronto-striatal system. Finally, we investigated the relationship between striatal dysfunction with structural brain changes. The results from the meta-analysis showed that HIV consistently affects the fronto-striatal system based on past fMRI studies. In subsequent studies, we demonstrated diminished functioning of the fronto-striatal networks involved in inhibition of voluntary movement as well as reward processing. Furthermore, this fronto-striatal dysfunction was also related to cortical atrophy often seen in HIV. Based on these findings, I therefore conclude that fronto-striatal dysfunction is a core component of HIV infection and needs to be considered in the assessment and management of all patients afflicted by this still very prevalent illness.