102 research outputs found

    An exploration of SSVEPs across development and autism spectrum conditions

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    This thesis contains an experimental investigation of networks dynamics across development and autism spectrum disorders (ASD). The interplay between functional segregation and integration within functional cortical networks was investigated based on the hypothesis that it plays a key role in development and ASD. Functional segregation refers to the synchronization between adjacent brain areas and functional integration indicates the synchronization between distributed brain regions. Steady-state visual evoked potentials (SSVEPs) to high contrast (90%) luminance and isoluminant chromatic (red-green) vertical gratings with two spatial frequencies (2.8 and 6 cpd) at 7.5 Hz (luminance) and 3.3 Hz (chromatic) were recorded in individuals with and without ASD. SSVEPs were analysed in the frequency and time domains to carrying out a detailed analysis of the dynamic functional connectivity elicited by perception of simple and complex visual stimuli. The first research study explored aged-related changes in networks dynamics. Participants were 30 children aged 7 to 17 and 11 adults from the typical population. Our results suggest functional reorganization from local to distributed networks across development, and that networks underpinning medium spatial frequency change would be a useful biomarker of typical brain function. The second research study explored potential changes in networks dynamics between children with and without ASD. Participants were 20 children aged 7 to 17 (10 with ASD and 10 age-matched typically developing). The result of this study is a potential EEG biomarker to characterize atypical brain function in autism. Our results suggest a direct relationship between functional segregation and functional integration during visual perception; atypical functional connectivity in lower processing mechanisms might contribute to the disruption in long-range functional integration reported in ASD, because both abnormalities occur in concert in the autistic brain. Overall this exploratory research shows that SSVEPs can elicit different functional networks involving local and distributed cortical brain systems, and can also show segregated and overlapping functional networks underlying neural mechanisms at early stages of visual processing during development and ASD. Therefore, SSVEPs would be a potentially useful technique to identify differences in the brains of people with and without autism

    Abilities to explicitly and implicitly infer intentions from actions in adults with autism spectrum disorder

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    Previous research suggests that Autism Spectrum Disorder (ASD) might be associated with impairments on implicit but not explicit mentalizing tasks. However, such comparisons are made difficult by the heterogeneity of stimuli and the techniques used to measure mentalizing capabilities. We tested the abilities of 34 individuals (17 with ASD) to derive intentions from othersā€™ actions during both explicit and implicit tasks and tracked their eye-movements. Adults with ASD displayed explicit but not implicit mentalizing deficits. Adults with ASD displayed typical fixation patterns during both implicit and explicit tasks. These results illustrate an explicit mentalizing deficit in adults with ASD, which cannot be attributed to differences in fixation patterns

    The Neural Basis of Mentalizing Deficits Experienced by Adults with Autism Spectrum Disorder

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    Adults with autism spectrum disorder (ASD) are widely regarded to exhibit difficulties inferring the internal states of others; known as ā€˜mentalizingā€™. However, the existing literature is inconsistent regarding the nature of the mentalizing difficulties experienced by adults with ASD. Two neural systems; the mirror neuron system (MNS) and the mentalizing system, are both thought to play important roles in inferring othersā€™ internal states from their actions but the precise roles of these systems and the nature of the interaction between them are unknown. The aim of this thesis was to explore the nature of mentalizing deficits associated with ASD, delineate between existing models of MNS involvement in mentalizing and identify the neural basis of mentalizing difficulties associated with ASD. The first empirical chapter presents two behavioural experiments which found adults with ASD were impaired at explicitly inferring the intentions of others from their actions. The second empirical chapter presents a transcranial magnetic stimulation (TMS) experiment which identified mentalizing-induced modulation of MNS activity, at the end of observed actions, in typically developing participants. The third empirical chapter presents an experiment which used TMS and electroencephalography (EEG) to measure MNS activation in adults with ASD when mentalizing and found higher levels of autistic traits predicted lower right-lateralised MNS activity. The final empirical chapter presents a functional magnetic resonance imaging (fMRI) experiment which identified higher levels of autistic traits predicted reduced functional connectivity between the MNS and the mentalizing system. Collectively, these data suggest that connectivity between the MNS and the mentalizing system is higher when inferring intentions of others from their actions, the interaction between the two systems may be best conceptualised within a predictive coding framework and reduced connectivity between these systems may underlie the mentalizing difficulties adults with ASD experience

    Investigating the effects of neuromodulatory training on autistic traits: a multi-methods psychophysiological study.

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    Autism spectrum disorder (ASD) is characterized by noticeable difficulties with social interaction and communication. Building on past research in this area and with the aim of improving methodological perspectives, a multi method approach to the study of ASD, mirror neurons and neurofeedback was taken. This thesis is made up of three main experiments: 1) A descriptive study of the resting state electroencephalography (EEG) across the spectrum of autistic traits in neurotypical individuals, 2) A comparison of 3 EEG protocols on MNs activation (mu suppression) and its difference according to self-reported traits of autism in neurotypical individuals, and 3) Neurofeedback training (NFT) on individuals with high autistic traits. In chapters 3 and 4 we employed simultaneous monitoring of physiological data. For chapter 3 EEG and eye-tracking was used, In the case of chapter 4, EEG and eye-tracking as well functional near infrared spectroscopy (fNIRS). Overall the findings revealed differences in mu rhythm reactivity associated to AQ traits. In chapter 2, the rEEG showed that individuals with high AQ scores showed less activation of frontal and fronto-central regions combined with higher levels of complexity in fronto-temporal, temporal, parietal and parieto-occipital areas. In chapter 3, EEG protocols that elicited Mu reactivity in individuals with different AQ traits suggested that as the AQ traits become more pronounced in neurotypical population, the event-related desynchronization (ERD) in low alpha declines. Chapter 3 was also the basis for the choice of pre/post assessment for chapter 4. In chapter 4 the multi-method physiological approach provided parallel physiological evidence for the effects of NFT in sensorimotor reactivity, namely, an increase in ERD in high alpha, higher levels of oxygenated haemoglobin and changes to the amplitude and frequency in the microstructure of mu for participants who underwent active training as opposed to a sham group

    Combined measures of oxygenation, haemodynamics and metabolism to understand neural responses in infants

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    fNIRS is an established research tool used to investigate typical and atypical brain development.Primarily, it provides measures of haemodynamic changes that are used to indirectly infer neural activity. Broadband NIRS provides a more direct marker of neuronal activation through measurement of changes in cytochrome-c-oxidase (CCO). As a cellular measure, CCO can be used as a bridge to improve our understanding of the link between neural and haemodynamic activity or ā€œneurovascular couplingā€. Study 1 demonstrated that changes in mitochondrial activity could be measured alongside haemodynamics during functional activation, over the temporal cortex, using a miniature system in four-to-six-month-old infants. In order to investigate the spatial specificity of CCO, its relation to haemodynamics and to build upon our understanding of neurovascular coupling mechanisms, multi-channel broadband NIRS was used alongside EEG in Study 2 where responses were measured over the visual cortex. Study 2 was performed in adults as the development of a concurrent NIRS and EEG protocol was methodologically challenging. Following this, Study 3 extended on experimental paradigms from Studies 1 and 2 to measure changes in metabolic activity and haemodynamics over the temporal and visual cortices, in four-to-seven-month-old infants. This study demonstrated simultaneous broadband NIRS and EEG use in infants for the first time. The results provided evidence of underdeveloped coupling of cerebral blood flow changes and mitochondrial activity in early infancy. Finally, Study 4 extended the protocol to investigate underlying biological mechanisms that may be altered in neurovascular coupling in autism, by studying infants at high familial risk for the disorder. The findings demonstrated that the combined protocol was not only feasible for use to study atypical brain development but also provided preliminary evidence of altered coupling between cerebral energy metabolism and haemodynamics.Taken together, this work illuminates hitherto undocumented evidence of neurovascular coupling during brain development and highlights the potential of using broadband NIRS with EEG for future neurodevelopmental research in typical and atypical populations

    Emotion attribution from facial expressions in individuals with social communication

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    Social communication impairment (SCI) is recognised as the core deficit in all autism spectrum disorders (ASD). Social communication involves the perceptual, emotion and cognitive processing of the facial expressions of other people to attribute the correct emotion. Activation in these three regions of interest (ROI) is, potentially, informative when investigating the underlying aetiology of SCI. Therefore, they were chosen a priori as ROI during the attribution of emotion attribution from facial expressions with the categorical and dimensional studies respectively. In the categorical studies, 16 high functioning individuals with an ASD diagnosis and 10 typically developing controls attributed emotion from static facial expressions while neural activation in these three hypothesis-driven ROI was measured. Individuals with ASD demonstrated comparable expertise and had comparable ROI activation during the emotion attribution task that required configural processing [the emotion label task]. However, these same individuals demonstrated reduced expertise and reduced right FG activation during the emotion attribution task that did not require configural processing [the emotion match task], and reduced right FG activation in a task that required them to attend to the eyes region of the face to attribute gaze direction. The findings provided evidence that individuals with ASD configurally process face percepts when necessary for the completion of the task, but use atypical face processing strategies in tasks that have greater perceptual load and do not necessitate configural processing. These findings support that task-dependant perceptual processing abnormalities in ASD are not related to reduced attention to the eyes region of the face per se; however, did not rule out that these abnormalities may relate to reduced configural processing/ attention to the whole face stimuli in individuals with ASD. The dimensional studies were undertaken to further investigate the relationship between FG responsivity and expertise in the attribution of emotion from facial expressions. These facial expressions, which were presented in a paradigm called the Dynamic Facial Expression Paradigm (DFEP), required configural processing and continuous attention to the whole face. Individuals with SCI had a similar capacity to accurately attribute emotion from non-inverted dynamic facial expressions as their brothers. Although there was no statistically significant difference in expertise between the proband and brother group, the trend toward increased response time in the non-inverted condition of the DFEP in the SCI group suggests the use of an accuracy/ response time trade-off strategy. SCI was directly correlated with right FG activation across the groups and the proband group activated significantly greater right FG activation to achieve a comparable level of performance as the brother group in the non-inverted condition of the DFEP. This finding may be related to increased configural processing and/ or the greater attentional demands inherent in attributing emotion from non-inverted dynamic facial expressions. The inverse was found in the inverted condition of the DFEP providing evidence for different perceptual processing strategies between groups when also processing inverted dynamic facial expressions. Both the categorical and dimensional studies provide evidence in support of the functional specialisation of the right FG for the configural processing of facial expressions, and atypical task-dependent perceptual processing in these high functioning individuals with SCI. Differing configural processing and attentional demands inherent in the experimental paradigms and atypical perceptual strategies offer possible explanations for atypical perceptual processing and differing right FG activation seen in these and other studies of face and facial expression processing (6-8). In the future, larger studies are required to further investigate accuracy/ speed trade-offs and determine if high functioning individuals with SCI are less expert in the attribution of emotion from facial expressions. Connectivity and fMRI studies utilising experimental designs such as parametric load analysis and incorporating eye-tracking technology are also required to further elucidate the relationship between behaviour, cognition, and neural function in individuals with SCI. Specifically, further integrated research is needed to determine the relationship between right FG activation, configural processing of facial expressions and attention to faces in individuals with SCI

    Implicit social cognition in autism spectrum disorder

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    Implicit learning about peopleā€™s states of mind relies inherently on associated emotions and affective valences, with abstract concepts such as disposition, attitude and intention being an intrinsic part of what is learned. Yet, similarly to studies aiming at the typically developed population, nearly all implicit learning studies on individuals with Autism Spectrum Disorder (ASD), are limited to the non-social domain, neglecting the possibility of domain-specific implicit learning impairments. Human behaviour is variable and complex and therefore detecting regularities in social interactions may be more challenging than in the physical world, which is largely governed by predictable laws.This project employed a novel implicit learning paradigm to evaluate implicit learning abilities in the social and non-social domains in typically-developed individuals with varying levels of ASD traits and individuals with a clinical diagnosis of ASD.The results revealed that impairments in implicit learning in ASD individuals emerge with respect to implicit social learning, with intact implicit learning abilities in the non-social domain. Deficits in implicit social learning were observed despite the participantsā€™ ability to correctly identify facial expressions, gaze direction and identities of the characters used in the studies. These findings extrapolated to typically-developed individuals high in ASD traits, suggesting a gradient of social implicit learning ability that runs throughout the population.The relative contributions of three potential mechanisms underpinning implicit social learning were examined: (i) contingency learning per se, (ii) contribution of other cognitive processes such as memory for facial expressions and social attention, (iii) implicit affective tagging. The evidence suggests that individuals with ASD may be impaired in their ability to implicitly incorporate affective values into cognitive processing, supporting the implicit affective tagging hypothesis. I argue that ASD individuals use alternative strategies to comprehend othersā€™ minds, relying more on physical characteristics, rather than socio-emotional meaning
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