Browsing by Author "Thomas, Kevin"
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- ItemOpen AccessAllocentric spatial memory following anterior temporal lobectomy: A comparison between active and sedentary epileptic adults(2009) Cotton, Sarah; Thomas, KevinThe association between neural activity of the left hemisphere hippocampal region and verbal memory has been well established. Similarly, neuropsychological outcomes following left anterior temporal lobectomy (ATL) have been well documented, with deficits in the ability to learn new verbally encoded material consistently displayed. However, the association between non-verbal memory and functioning of the right hemisphere hippocampal region and, consequently, neuropsychological outcomes following right ATL, remains an area of debate. Moreover, relatively new evidence suggests that physical activity could improve overall hippocampal function (McCloskey, 2003). Therefore, the aim of the present study was to investigate spatial cognition in patients with intractable epilepsy and also to establish whether physical activity levels of these patients, i.e. active versus sedentary, had an effect on neuropsychological functioning. Spatial and verbal cognition were assessed in three groups: a pre-surgical (awaiting ATL) group, a post-surgical (following ATL) group and a healthy control group. Physical activity levels of all participants were established and left-sided damage and right-sided damage patient groups were divided into those with moderate-to-high activity levels and those with low activity levels. Results showed that on tests of spatial cognition, patients with right-sided damage tended to show more deficits than patients with left-sided damage when assessed using experimental tasks. However, no group differences were found when using standard clinical tests for assessment. On tests of verbal memory, patients with left-sided damage displayed more deficits than patients with right-sided damage. Patients with moderate-high activity levels performed better than patients with low activity levels on tests of spatial cognition, but both groups performed similarly on tests of verbal memory. The data therefore largely confirm the hypotheses. This is the first demonstration, within a single study, of spatial memory deficits using a virtual environment spatial navigation task in epileptic adults; and of an association between activity levels and improved spatial cognition on the CG Arena task in epileptic adults.
- ItemOpen AccessAn Evaluation of the Psychometric Properties of the Montreal Cognitive Assessment Tool when Administered in a Memory Clinic At Groote Schuur Hospital, Cape Town, South Africa(2022) Thungana, Yanga; Joska, John; Thomas, KevinWorldwide, the population is aging, and the prevalence of neurocognitive disorders is expected to rise exponentially. Therefore, early detection of dementia is favorable for the patient and may even be of greater significance if disease-modifying treatments are discovered. The Montreal Cognitive Assessment (MoCA) is a reliable and valid cognitive screening tool but is sensitive to several sociodemographic factors, including language, culture, and quality of education. This underscores the need for cognitive screening scales validated in the culturally diverse South African setting. Aim. The purpose of this study was to investigate the utility of the MoCA as a brief cognitive screening tool in a specialized clinical South African sample. Methods. A retrospective medical folder review of 162 patients seen at Groote Schuur Hospital Memory Clinic for the first time between January 2014 and August 2021. Results. The median age of participants was 67 years (IQR 58-73). Most were females (63%, n =102), and had dementia (58%, n = 94); more than half (51%, n = 78) had at least 12 years of formal education. Older age and lower levels of education were associated with lower MoCA scores (p < 0.001). Conclusion. In a specialized South African clinical setting, the MoCA demonstrated good psychometric properties as a screening tool for evaluating different levels of cognitive impairment. However, to our knowledge, this is the first South African study to assess the factor structure of the MoCA in a clinical setting. More comprehensive and larger studies should evaluate the validity of our findings.
- ItemOpen AccessAssociations between sleep and cognitive-affective functioning in Posttraumatic Stress Disorder(2017) Lipinska, Malgorzata; Thomas, KevinThe current research tested the proposition that the sleep disruption characteristic of posttraumatic stress disorder (PTSD) has discrete, predictable, and significant effects on the processing of neutral declarative memory, emotional memory, and emotional reactivity. Research spanning multiple neuroscientific literatures demonstrates that healthy, uninterrupted sleep is critical for memory consolidation and emotional regulation, and that PTSD-diagnosed individuals experience sleep disruption, memory deficits, and emotional dysregulation. To test whether these behavioral, cognitive, and affective characteristics of PTSD are meaningfully related, I recruited three groups of participants: PTSD (n = 21), trauma-exposed non-PTSD (TE; n = 19), and healthy controls (HC; n = 20). Each participant was assessed before and after an 8-hour period of sleep and an 8-hour period of waking activity. The assessment featured measures of neutral declarative memory (learning of stimuli before the delay, and a free recall task afterward), emotional memory (exposure to highly-arousing negatively valenced, highly-arousing positively valenced, and low arousing neutral pictures before the delay, and a recognition task afterward), and emotional reactivity (physiological responses to the emotional pictures, both before and after the delay). The results are presented under the headings of four investigations. Investigation 1, which focused on objective and subjective sleep quality, suggested that PTSD-diagnosed participants had decreased sleep depth in comparison to HC participants, but presented with no other evidence of objective sleep disruption. Furthermore, PTSD-diagnosed participants reported better subjective sleep quality in the sleep laboratory than in their home environment, an effect not observed in TE and HC participants. Investigation 2, which focused on neutral declarative memory, suggested that after a sleep-filled, but not wake-filled, delay, PTSD-diagnosed participants retained less neutral declarative information than TE and HC participants. Furthermore, increased fragmentation of rapid eye movement (REM) sleep in PTSD-diagnosed individuals was a significant predictor of post-sleep memory retention deficits. In contrast, Investigations 3 and 4 suggested no significant between-group differences in emotional memory or emotional reactivity. However, Investigation 3 suggested that, after a sleep-filled delay, pictures of all valence and arousal categories were recognized equally accurately by all participants. In contrast, after a wake-filled delay all participants had higher recognition accuracy for negative pictures. Furthermore, Investigation 4 suggested that a sleep-filled delay attenuated emotional reactivity to pictures of all arousal and valence categories, whereas a wake-filled delay was associated with a rise in emotional reactivity across the day. Together, these results suggest that fairly small sleep disruptions (specific to REM-related changes) in PTSD-diagnosed individuals will affect retention of neutral declarative information, but will have no significant effects on the processing of, or reactivity toward, arousing and valenced stimuli. Overall, these findings allow the conclusion that, in PTSD, the co-occurrence of sleep and neutral declarative memory difficulties is not accidental – that is, these two symptom clusters are meaningfully related. Furthermore, the results demonstrate that a reasonable, not necessarily perfect, night of sleep in PTSD is associated with intact functioning within certain cognitive and affective domains. The research bolsters the neuroscientific view of sleep as a critical biological process linked integrally to psychological well-being.
- ItemOpen AccessAssociations between sleep architecture, cortisol concentrations, cognitive performance, and quality of life in patients with Addison's disease(2019) Henry, Michelle; Thomas, Kevin; Ross, Ian; Wolf, PedroRecent literature in the neurosciences suggests that there are mechanistic relations between sleep disruption and cognitive (particularly memory) deficits, and that varying concentrations of the hormone cortisol may play a particularly important role in mediating those relations. Because patients with Addison’s disease (AD) experience consistent and predictable periods of sub- and supra-physiological cortisol concentrations (due to lifelong glucocorticoid replacement therapy), and because they frequently report disrupted sleep and poor memory, those presenting with that endocrinological disorder form an ideal population to use in studies testing hypotheses about the ways in which (a) disrupted sleep is related to impaired consolidation of previously learned material (and, hence, poor performance on tests assessing memory for that material), and (b) cortisol concentrations may mediate this relationship between sleep and memory. This dissertation presents four studies that, together, tested those hypotheses. Study 1 (n = 60 per group) found that patients with AD self-reported significantly more disturbed sleep and poorer cognition and quality of life compared to matched healthy controls. Importantly, our analyses suggested that disrupted sleep, and not AD per se, accounted most strongly for the reported cognitive impairment. Study 2 (n = 35 per group) found that patients had significantly poorer objectively-measured declarative memory performance compared to matched healthy controls, but that other domains of cognition were relatively unimpaired. Study 3 (n = 10 per group) suggested that matched healthy controls retained significantly more declarative information than patients. Importantly, while controls retained significantly more declarative information when a period of sleep, rather than waking, separated learning from recall, patients derived no such benefit. Study 4 (n = 7 per group) suggested that, relative to matched healthy controls, patients had different patterns of night-time cortisol secretion, accompanied by significantly reduced slow-wave sleep. Together, these four studies suggest that, despite being on replacement medication, patients with AD still experience disrupted sleep and memory deficits. These disruptions and deficits may be related to the failure of replacement regimens to restore a normal circadian rhythm of cortisol secretion. This pattern of results provides support for existing theoretical frameworks which posit that (in AD and other neuroendocrine, neurological, or psychiatric disorders) disrupted sleep is an important biological mechanism that underlies, at least partially, the memory impairments that patients frequently report experiencing. With specific regard to patients with AD, the findings presented here suggest that future initiatives aimed at improving patients’ cognitive performance (and, indeed, their overall quality of life) should prioritise optimizing sleep. More generally, this dissertation advances our understanding of sleep as a critical biological process essential for cognitive well-being.
- ItemOpen AccessDisinhibition in South African treatment-naïve adolescents with alcohol use disorders(2012) Cuzen, Natalie; Thomas, KevinThe concept of the disinhibitory complex refers to a cluster of personality, psychiatric, cognitive, and electrophysiological inhibitory control impairments that have been documented in alcohol use disorders (AUDs). Previous AUD research has focused on treatment-seeking adults with comorbid psychopathology; with regard to the disinhibitory complex, such individuals are likely to differ from younger, treatment-naïve individuals, such as the sample here studied. Further, few studies have examined several domains of disinhibition simultaneously, and so little is known about relationships between the various correlates of disinhibition. This study aimed to (a) examine and characterize the disinhibitory complex in treatment-naïve adolescents with AUDs, (b) investigate sex differences in disinhibition, and (c) determine whether an underlying construct of disinhibition might explain elevated levels of disinhibition in AUDs observed on individual indices.
- ItemOpen AccessThe effect of early adversity on adult spatial cognition : a functional magnetic resonance imaging study(2009) Dey, Marc; Thomas, Kevin; Meintjies, ErnestaExposure to traumatic childhood events can lead to a range of behavioural, psychological, and physiological consequences. Previous studies have shown that neurobiological changes in reaction to severe stress may cause lasting damage to particular neural regions, including the hippocampus and the prefrontal cortex. It has been suggested that such damage to these regions results in difficulties in associated cognitive functioning, including problems with verbal declarative memory and cognitive control. Little focus has been placed on visualspatial cognition in traumatised individuals, however. The aim of this project, which comprised two studies, was to investigate visual memory and spatial cognition in adult survivors of childhood trauma. Study 1 compared the performance of 23 individuals who had experienced childhood abuse (the Trauma group) to 38 matched controls with no such experience (the Control group) on the four visual-spatial memory tasks of the Cambridge Neuropsychological Test Automated Battery (CANTAB). Results suggested that participants in the Trauma group showed poorer performance on two of the more complex tasks, which tapped both hippocampal and prefrontal cortex functioning, compared to the controls. One interpretation of this finding is that these between-group differences reflect the dysfunction of a network involved in visual-spatial memory in individuals who have experienced childhood trauma. Study 2 used functional magnetic resonance imaging (fMRI) to investigate whether any marked differences in neural activation would be evident between individuals with a history of childhood trauma (n = 7) and matched controls with no such history (n = 14) during spatial navigation tasks. Functional images were gathered while participants completed two spatial navigation tasks: the Computer-Generated Arena (CG Arena), a smallscale spatial navigation task, and the Virtual City, a large-scale spatial navigation task based on an environment created by Maguire et al. (1998). Although no significant behavioural differences were evident during the completion of these tasks, the fMRI data did show marked differences in activation. These results of the CG Arena, in particular, showed lower activation in PFC areas, including the anterior cingulate cortex, during wayfinding tasks. Taken together, the results of these two studies suggest that (a) subtly impaired neural functioning is evident in individuals with a history of childhood trauma, and (b) this impairment may lead to difficulties in successfully completing complex visual-spatial memory and spatial navigation tasks.
- ItemOpen AccessThe effects of acute stress on retrieval of visual and spatial material(2015) Du Plooy, Christopher P; Thomas, KevinPreviously published studies, using human and non-human animal samples, suggest that stress impairs memory retrieval. However, most human studies that report these impairing effects explore verbal memory only. The aim of the studies reported in this dissertation was to explore the effects of an acute stressor (Study 1), and of administration of prednisone (Study 2), on retrieval of visual-spatial material (both emotional and neutral), and to compare the findings against three theories that attempt to account for the effects of stress on memory: the inverted-U hypothesis (de Kloet et al., 1999), hot-cool theory (Jacobs & Metcalfe, 1998), and the integrated vertical and horizontal perspective theory (Schwabe et al., 2012). To explore the research question, I aimed to systematically replicate, in humans, the pioneering study of de Quervain et al. (1998). They demonstrated that both stress (in the form of foot-shocks) and glucocorticoid treatment impaired memory retrieval, as demonstrated by water maze performance, in rodents. To replicate their design for use in humans, I needed to make several apparatus substitutions. Hence, before embarking on the major studies that constitute the dissertation, I undertook two pilot/preparation studies. Study A verified that a novel visual and spatial task (a virtual environment (VE) water maze task) was a suitable human analog for the Morris Water Maze. Twenty-four participants learned the location of a target in three different VE rooms. Landmarks in the first room were neutral non-arousing pictures; in the second, pleasant arousing pictures; and in the third, unpleasant arousing pictures. Emotional content of landmarks did not affect place learning, although the women demonstrated better recognition for arousing than neutral landmarks. Study B verified that a novel laboratory-based stressor was a suitable substitute for the foot-shock stressor. This novel stressor combines the Cold Pressor Test with the Trier Social Stress Test (TSST) into a single procedure: the Fear Factor Stress Test (FFST). Ninety participants completed one of three conditions: FFST-Stress, FFST-Control, or TSST. The FFST-Stress induced a more robust and sustained cortisol response than the TSST (without increasing participant discomfort), while the FFST-Control condition did not provoke a cortisol response. Following these validation studies, Study 1 explored the effects of the FFST on memory retrieval for the VE rooms created in Study A. Sixty participants learned the location of an invisible target in the VE rooms and, 24 hours later, after undergoing either the FFST-Stress or -Control conditions, completed a set of navigational, recall, and recognition memory tests. In Study 2, the FFST conditions were substituted by a 25mg prednisone dose and a placebo. Following ingestion of the prednisone/placebo, 60 participants completed the same set of navigational and memory tests. Results revealed that neither acute stress nor prednisone administration impaired visual and spatial memory. However, exposure to the acute stressor appeared to enhance verbal memory in women, and prednisone administration appeared to impair verbal memory in both men and women. Relating the current findings to theory revealed that only the inverted-U hypothesis was capable of accounting for the observed pattern of data with regard to verbal memory. Specifically, congruent with predictions derived from that theory, a combination of low levels of endogenous cortisol due to the time of day when procedures were performed, along with the dose-dependent effects of cortisol, might account for the contrasting verbal memory findings seen across Studies 1 and 2. However, none of the three theories were capable of explaining the absence of stress effects on visual and spatial memory. Findings from Studies 1 and 2 therefore suggest that being exposed to an acute stressor or being administered prednisone might have had varying effects across memory domains, which is consistent with a functional perspective on memory. These findings indicate that further investigation into domain-specific effects of stress on memory might be a rewarding area of inquiry.
- ItemOpen AccessEffects of Menstrual Cycle Phase and Stress on Spatial Navigational Strategy Use(2020) McHale, Alexandra Lauren; Thomas, KevinPrevious research suggests there are significant effects on spatial navigation of menstrual cycle phase and, independently, of stress exposure. However, no published study explores how these variables might interact to affect human navigational strategies. Such exploration is important because women experience stressful events throughout the menstrual cycle. Hence, the primary aim of the research described here was to investigate the potentially interacting effect of menstrual cycle phase and acute psychosocial stress on allocentric (i.e., relying on a cognitive map of the environment, created using distal cues), egocentricresponse (i.e., relying on body-turn directions), and egocentric-cue (i.e., relying on the location of specific proximal cues) navigation. The study tested three hypotheses: (1) menstrual cycle phase will significantly affect navigational strategy (women in the early follicular and ovulatory phases will prefer egocentric strategies, whereas those in the mid/late luteal phase will prefer an allocentric strategy); (2) stress will significantly affect navigational strategy (women exposed to an acute psychosocial stressor will prefer egocentric strategies while those unexposed will prefer an allocentric strategy); and (3) there will be a significant interaction effect on navigational strategies (particularly, women in the mid/late luteal phase will use egocentric strategies when stressed and allocentric strategies when not). Naturallycycling young adult women (N = 60), each in either the early follicular, ovulatory, or mid/late luteal phase of the cycle, were randomly assigned to either a stress-exposure condition (the Paced Auditory Serial Addition Task [PASAT], which required them to rapidly add pairs of verbally presented digits at increasing between-digit intervals) or an equivalent control condition (the un-PASAT, which required them to add pairs of digits at a constant, slower, between-digit speed). Hence, the study groups were: Early Follicular+Stress (n = 11), Early Follicular+Non-Stress (n = 10), Ovulatory+Stress (n = 8), Ovulatory+Non-Stress (n = 8), Mid/Late Luteal+Stress (n = 12), and Mid/Late Luteal+Non-Stress (n = 11). After the manipulation, they completed the Hex Maze, a virtual environment navigation task. The task comprises 10 trial pairs. On the first trial of a pair, participants learn a target platform's location. On the second, they must navigate back to that location. This latter trial can be completed using either an allocentric, egocentric-response, or egocentric-cue strategy. Results suggested that the PASAT successfully induced psychological and physiological stress. A mixed linear model analysis detected, with regard to the navigational strategy outcome variables, no significant main effect of menstrual cycle phase (a result inconsistent with previous research), no significant main effect of stress exposure (a result consistent with some prior research), and no significant interaction effect. Although the interaction was non- significant, trends within the data suggested the results followed the predicted direction. Hence, this relatively small-scale study may serve as a foundation for future research as it provides valuable hypothesis-generating insight into the possible interaction of menstrual cycle phase and stress, and encourages the further investigation of this topic.
- ItemOpen AccessEffects of methamphetamine on prenatally exposed children in Cape Town: cognition and intrinsic functional brain connectivity(2015) Kwiatkowski, Maja Anna; Thomas, Kevin; Roos, Annerine; Ipser, JonathanMethamphetamine use among pregnant women is an increasing problem in South Africa. The aim of this cross-sectional exploratory study was to examine the possible neurotoxic effects of prenatal methamphetamine exposure (PME) on cognition and the developing brain in a sample of affected children in Cape Town, South Africa. Thus, this is a two-part study: the first part examines the effects of PME on neuropsychological outcomes, and the second part examines the effects of PME on intrinsic functional brain connectivity. Children with PME (n = 23) and unexposed controls (n = 22) completed a battery of neurocognitive assessments, and a smaller sub-sample (n = 36; 19 children with PME, 17 unexposed controls) also underwent resting-state functional magnetic resonance imaging (RS-fMRI). Independent samples t-tests revealed that children with PME scored significantly more poorly on measures of IQ, learning and memory, confrontation naming, visual-motor integration, and fine motor co-ordination, when compared to controls. Hierarchical regression analyses confirmed that PME has a significant effect on cognitive performance, and that this effect largely withstands the effects of potentially confounding sociodemographic and anthropometric variables. Independent component analyses revealed significant betweengroup differences in functional brain networks detected in task-free RS-fMRI in children with PME. Specifically, there is evidence for compromised connectivity within and between the basal ganglia network and default mode network in children with PME. Overall, the findings contribute to the small but growing literature on the cognitive effects of PME. The current study is the first to document preliminary evidence indicating aberrant intrinsic functional brain connectivity in children with PME, and suggests that further investigation of potential associations between particular neurocognitive deficits and such aberrant connectivity might be warranted.
- ItemOpen AccessThe effects of partner type on condom choice and condom use(2010) Zondo, S; Thomas, KevinSouth Africa has one of the world's highest rates of HIV infection. Little previous research has focused on the relationship between individuals in different sexual contexts and their attitudes toward condom choice. I tested the hypotheses that (a) implicit and explicit measures of attitudes towards condom choice would show that individuals in casual sexual contexts, compared to those in the context of exclusive sexual relationships, would spontaneously associate more strongly with brand-name condoms over generic condoms, and (b) there would be a positive correlation between explicit and implicit attitudes towards condom choice.
- ItemOpen AccessThe effects of racial group membership and cognitive load on empathy and helping behaviour(2016) Subramoney, Sivenesi; Thomas, Kevin; Fourie, Melike MaretheResearch suggests that people feel more empathy for racial in-group compared to racial outgroup members, and in some circumstances, are more likely to help racial in- than out-group members. Furthermore, there is evidence that cognitive load may also attenuate helping behavior. Research is yet to establish the influence of both racial group membership and cognitive load on empathy and helping, however. In this study, a sample of 104 women (52 Black and 52 White) completed either a Low or a High cognitive load task and then viewed video clips depicting racial in- and out-group members in distress. I measured participants' selfreported empathy, physiological activity, and willingness to help those in distress. The results did not show the expected racial bias in empathic responding, but rather, indicated heightened empathy (seen in both self-reported and physiological responses) for the Black target individual, regardless of participant race. Secondly, although cognitive load did not influence empathic responding, participants in the High Load condition were less likely to offer help than participants in the Low Load condition. Finally, correlation data suggest that racial group membership and cognitive load contributed to the associations between individual differences (i.e., in ethnic identification, motivations to respond without prejudice, and trait empathy), empathic responding, and helping behavior. Overall, the findings contribute to a growing literature on cross-racial empathy, and highlight the complex physiology underlying our empathy for others.
- ItemOpen AccessEmergency service workers' coping in response to traumatic events : associations with psychiatric symptoms(2007) Stanley, C J; Ward, Catherine; Thomas, KevinThis study aimed to explore the relationship between coping strategies and posttraumatic symptomology in emergency service workers in the Western Cape. Three fundamental coping strategies were assessed: seeking social support, problem-solving, and avoidance. I hypothesised that seeking social support and problem-solving would be associated with decreased levels of psychiatric symptoms, while avoidance would be associated with increased levels of psychiatric symptoms.
- ItemOpen AccessEvent-based prospective memory in fetal alcohol spectrum disorders(2013) O'Leary, Catherine; Thomas, Kevin; Jacobson, Sandra; Molteno, Christopher DLearning and memory seem to be particularly vulnerable to the effects of heavy prenatal alcohol exposure. Previous research has, however, been limited to the study of retrospective memory (i.e., episodic or declarative memory) in children with a history of prenatal alcohol exposure. Recently, memory researchers have turned their attention to the study of prospective memory (PM), or the ability to realize and act on delayed intentions, in clinical populations. There are no published studies exploring PM in FASD, however. Prospective remembering is reliant on declarative memory as well as intact executive functioning, both of which are known to be impaired in FASD. The current study aimed, therefore, to investigate event-based PM functioning in a longitudinal cohort of children with heavy prenatal alcohol exposure. It also aimed to investigate whether the relation between prenatal alcohol exposure and prospective memory was influenced by IQ, executive functioning, or retrospective memory.
- ItemOpen AccessExecutive dysfunction and weak central coherence : neither theory suitably explains a core cognitive deficit in autism spectrum disorders(2008) Daniels, Michelle; Thomas, KevinTheories of weak central coherence (WCC; a local detail-specific way of processing information that allows individuals to focus on and remember minutiae) and executive dysfunction (EF dysfunction; an inability to employ goal-directed cognition to plan, organize, and alternate between tasks, or to inhibit incorrect responses) largely dominate current understandings of the neurocognitive profile in autism spectrum disorders (ASD). Recent empirical evidence suggests, however, that neither theory adequately explains the uneven profile of autistic cognition (e.g., attention deficits and relative spatial strengths), and that neither is satisfactorily applicable to autistic individuals across the spectrum. Moreover, recent research provides results contradictory to those predicted by these theoretical frameworks. Consequently, the theories' validity as explanations of a core cognitive deficit in ASD has come into question. The current research attempts to resolve some of the questions raised by the shortcomings of these two theoretical frameworks. In addition, this research aims to investigate the nature of spatial cognition as an assumed strength following from reports of enhanced visiospatial skill in ASD. Twenty-five high-functioning autistic (HFA; IQ> 70), 16 low-functioning autistic (LFA; IQ::: 70), 13 Asperger's syndrome (AS), 13 mentally retarded (MR), and 22 typically developing (TD) children matched according to sex and handedness were assessed on a comprehensive battery of clinical and experimental neurocognitive measures. There were no group differences on the EF domain, attentional control. On the domains of cognitive flexibility and goal setting, participants in both the AS and LF A groups did not display the EF deficit predicted by the EF dysfunction theory when compared to IQ-matched controls. Results: The only support shown for EF dysfunction was with HF A children. These participants made significantly more perseverative errors on the Wisconsin Card Sort Test64 (WCST64 ) as an outcome variable of cognitive flexibility and performed more poorly on the Tower of London (ToL) total correct (cognitive flexibility) and total time (goal-setting) scores than controls, without the influence of IQ. In terms of WCC, AS and LF A participants performed no better than IQ-matched controls on visuo-spatial tasks- the Block Design (BD), Rey-Osterrieth Complex Figure Test (ROCF), and Children's Embedded Figures Test (CEFT). Broader spatial cognition was similarly intact but not superior in AS and LF A participants. On those spatial measures not influenced heavily by intelligence, the HF A group were shown to have a diminished capacity for allocentric spatial cognition compared to controls. The results of this investigation provided only partial support for the theory of EF dysfunction and no support for the theory of WCC. Instead, they suggest that neither theory is suitable as an explanation of a core cognitive deficit in ASD.
- ItemOpen AccessFamilies of children with traumatic brain injuries : stressors and needs in the South African context(2010) Oosthuizen, Deirdre; Thomas, Kevin; Schrieff, Leigh[Background] The effects of a traumatic brain injury (TBI) can be devastating not only for the child that sustains the injury but also for his or her family. A TBI can negatively affect a child cognitively, emotionally, and behaviourally. In developing countries such as South Africa these negative effects of TBI are often compounded by the impact of other health crises such as HIV / AIDS, as well as by the existence of relatively few economic resources and a lack of rehabilitation services. Injury-related consequences, further compounded by developing world contexts, seem to suggest that families of children with TBI have many stressors and strains that need to be addressed. Aims. The current study sought to explore the needs and stressors of caregivers of children with TBI, and how local contextual factors contribute to those needs and stressors. [Methods] The sample consisted of four groups (n = 18 caregivers in each). These four groups included parents/caregivers who cared for a child with either a mild head injury, a moderate/severe head injury, or an orthopaedic injury, and a control group of caregivers with healthy children. The Parenting Stress Index, Family Burden of Injury Interview, and Family Needs Questionnaire were administered to each participant. [Results] South African caregivers of children with TBIs are critically stressed. Much of their stress is related to the child's behaviour and ways of relating to their caregiver. Caregivers in the Moderate/Severe TBI group reported experiencing particular difficulty with their own reactions to the injury, and reported feeling depressed and incompetent, as well as isolated and restricted by their role as parent. Caregivers also reported experiencing a need for health information, professional support, community support, involvement in the child's care, and emotional support. They reported, however, that few of these needs were being met. Results also showed that South African caregivers of children with TBI displayed more stressors and needs than similar samples in developed countries. [Conclusions] We suggest that a better understanding of the experience of families of children with TBIs is needed amongst TBI service providers. It is hoped that this study's results will aid that understanding, and that they will provide information for policy makers who can set into motion a sequence of services that more adequately aid both the child with TBI and his/her family.
- ItemOpen AccessFunctional impairment in South African children and adolescents with obsessive-compulsive disorder(2009) Hoppe, Lara Judy; Thomas, Kevin; Lochner, ChristineThis research aimed to increase current understanding of functional impairment in children and adolescents with Obsessive-Compulsive Disorder (OCD). Twenty-six South African children and adolescents with OCD participated in the study. The Schedule for Affective Disorders and Schizophrenia for School-Age Children-Present and Lifetime Version (KSADS-PL), the Mini International Neuropsychiatric Interview For Children and Adolescents Version 5 (MINIKID5.0), the Children's Global Assessment Scale (CGAS), the Children's Yale-Brown Obsessive Compulsive Scale (CY-BOCS) and the Child Obsessive-Compulsive Impact Scale-Revised (COIS-R) were used to assess the children's and adolescent's past and current psychopathology, OCD symptom severity and OCD-related functional impairment. Findings suggest that most of the children (88.46%) in this study had one or more comorbid disorders. Parents and children agreed on very few of the rating items common the COIS-R-P and COIS-R-C. Parents, however, consistently reported higher rates of significant problems than did their children. Correlations between the various instruments revealed that parents are more accurate than their children in rating their child's global impairment and OCD-specific impairment. Therefore, collateral information from parents is vital for the clinician to accurately assess and fully understand the child's OCD-related functional impairment. Moreover, the number of comorbid disorders, and whether the child had ADHD or not, did not impact on the COIS-R total scores, suggesting that the COIS-R is a useful measure to assess OCD-specific impairment. Parents and children both reported that the most significant domain of impairment is the school domain. Moreover, parents reported that the most significant functional problem is "concentrating on his/her work" and children reported that the most significant functional problem is "getting good grades." Findings from studies such as this help clinicians to have a better understanding of childhood OCD-related functional impairment, which helps them to accurately diagnose and treat children with OCD.
- ItemOpen AccessFunctional impairment in South African children with Obsessive-Compulsive disorder and Attention-Deficit/Hyperactive Disorder(2009) Fischer, Mareli; Thomas, KevinThe electromagnetic pulse (EMP) resulting from the detonation of nuclear explosives is a documented and studied phenomenon. What is less well known and understood is the simi- lar yet considerably less powerful occurrence surrounding the detonation of high explosives. The phenomenon was rst noticed by Kolsky in 1954 during his investigation into stress waves using explosive charges. This project was undertaken to identify any discernible eld or wave in the low frequency EM spectrum, focusing particularly on the magnetic eld. The work published by Soloviev in 2002 and Adushkin in 2004 served as guidelines on test procedure and setup. Testing of this nature was not found in the literature to have been previously conducted in South Africa and is multi-disciplinary, involving the elds of detonics and signal processing. The test procedure implemented proved valid as signals were detected and su cient data were gathered to perform basic pattern recognition and spectral frequency analysis. The analysis allowed for comments to be made on the relationship between the signal and other characteristics surrounding the event. Inside the frequency band investigated there appeared to be two bands of activity in the kHz range, which is consistent with previously published works. The repeatability of the waveforms shape for identical blasts was good but with the limited sample size a proper database could not be developed. Provisionally it can be said that such events do have characteristic shapes. Testing revolved around small charges and was conducted in the near eld. This removed the possibility of commenting on orientation factors. The testing was a success in terms of recording magnetic eld signals from the detonation of high explosives.
- ItemOpen AccessGuilt in the body and brain : a psychophysiological and neuroimaging investigation(2011) Fourie, Melike Marethe; Thomas, KevinGuilt has been described as a quintessential moral emotion with an important regulatory function for the individual and society. Few studies have, however, empirically investigated guilt, largely because of challenges associated with its real-time elicitation. I aimed to elucidate the physiological and neural correlates of guilt by developing two novel emotion elicitation paradigms.
- ItemOpen AccessThe impact of acute psychological stress on declarative and working memory functioning(2010) Human, Robyn; Thomas, KevinPrevious research has shown that stress affects processing in many different memory systems. This study aimed to investigate the effects of acute psychosocial stress on declarative memory (DM) and working memory (WM) performance, and to explore whether sex differences exist under stress in these two memory systems. DM was assessed using cued recall and recognition of a verbal paired-associates list. WM was assessed using an n-back test with various difficulty levels. One hundred (42 males) undergraduate psychology students from the University of Cape Town were recruited. Phase of menstrual cycle and oral contraceptive use were controlled for in female participants. Participants took part in two sessions, 24 hours apart, each beginning after 16h00. Day 1 involved learning and immediate cued recall of the word pairs, and completing a practice n-back protocol. During Day 2, 45 participants were exposed to a psychosocial stressor and 41 were exposed to a relaxation period. Physiological and self-report measures of stress were taken at three intervals pre- and post-experimental manipulation. Participants then completed delayed cued recall and recognition tests for the previously-learned word pairs, and the full version of the n-back test. Data were analysed only for participants characterised as 'cortisol responders' following the experimental manipulation. The final sample included 57 participants (30 males). With regard to DM, stress did not affect either delayed cued recall or recognition performance in either men or women. With regard to WM, stress negatively affected accuracy among men, but not women. These results are largely consistent with previous literature, but also elucidate a sex difference in working memory performance under stress (viz., while men's performance is negatively affected by stress, women show improved performance). The study provides important evidence for sex differences in WM performance under stress, and highlights several methodological issues that should be addressed in future studies.
- ItemOpen AccessThe impact of acute psychological stress on spatial cognition(2008) Attwood, Carmela Bonito; Thomas, KevinBased on the premise that the hippocampus is both affected by cortisol and intimately involved in episodic memory and spatial cognition, the general aim of this study was to investigate the effects of psychosocial stress (and consequent cortisol increase) on spatial cognition and verbal memory in men and women. One group of 33 participants (16 males and 17 females) were exposed to the Trier Social Stress Test (TSST; Kirschbaum, Pirke, & Hellhammer, 1993), a procedure designed to induce mild psychosocial stress. I used 3 different means to check the effectiveness of this stress induction: salivary cortisol, self-report via the Spielberger State-Trait Anxiety Inventory, and heart-rate measurements. The measures all converged to suggest that the stress induction procedure was successful. A control group of29 participants (15 males and 14 females) was exposed to a relaxation period rather than the TSST. Following this part of the experimental protocol, all participants completed a virtual environment spatial navigation task and a word-list learning and recall task. Results showed that, on the spatial navigation task, females and males who were not exposed to the stressor located and relocated a hidden target equally well (Le., cognitive map-guided navigation was intact in unstressed participants). In addition, on the spatial navigation task the interaction effect of the gender and experimental condition approached statistical significance (p = 0.085), suggesting that females exposed to the stressor required more time to locate and relocate a hidden target than did the other participants (Le., they were disrupted in their cognitive map-guided navigation). On the verbal memory task, participants who showed larger cortisol increases following exposure to the TSST tended to recall fewer words than did those with smaller cortisol increases, with a slightly stronger negative correlation in males than in females. The data therefore confirm that stress impacts different memory systems in different ways, and, perhaps more importantly, that sex differences play a role in moderating those effects. This is the first demonstration, within a single study, of a possible double dissociation of sex differences in cognitive performance following induction of mild psychosocial stress.