Infant and toddler precursors of attentional processes in Fragile X syndrome: A neurodevelopmental perspective

With the recent sequencing of the human genome, the following question has attracted much interest: can the function of single genes be linked to specific neural and cognitive processes? Within this context, developmental disorders of known genetic origins have been used as naturally-occurring models to link the function (and dysfunction) of genes with cognition. Fragile X syndrome (FXS) is a genetically inherited disorder associated with the silencing of a single gene involved in experience-dependent changes at glutamatergic synapses. In adulthood, it is associated with core attentional difficulties accompanied by seemingly proficient visuo-perception, but the profile of infants and toddlers has not been investigated. In this thesis, fragile X syndrome is used as a tool to investigate how initial changes in a generalised property of all cortical neurones can nonetheless result, in the adult, in core difficulties in the control of attention. I argue that, even in disorders associated with the silencing of a single gene like FXS, the answer requires a developmental approach. Chapter 1 delineates a theoretical distinction between endogenous and exogenous influences on attentional control, whereas Chapter 2 defines methodological issues in assessing atypical attention, such as tools for the assessment of general developmental level and choices of control groups. Part II focuses on tasks tapping endogenous attention control. In particular, Chapters 3 and 4 examine the control of eye-movements and manual response conflict in infants and toddlers with FXS and in typically developing controls. In contrast, Part III concentrates on the exogenous effects of sudden peripheral onsets on visual orienting (Chapter 5) and of the perceptual salience of targets during visual search (Chapter 6). Finally, Part IV traces longitudinal changes in visual search performance. The findings suggest that, like adults with the syndrome, infant and toddlers with FXS display striking deficits in endogenous attention. However, unlike adults, infants are also characterised by atypical exogenous influences on attention and longitudinal changes in performance point to complex developmental relationships between early and later measures of attention. The findings are discussed in terms of their theoretical implications for fragile X syndrome and other developmental disorders affecting attention. They challenge the notion of direct genotype-phenotype mappings that fail to take development into account

Applying an Attentional Set to Perceived and Remembered Features

Previous research has examined our ability to attend selectively to particular features of perceptual objects, as well as our ability to switch from attending to one type of feature to another. This is usually done in the context of anticipatory attentional-set control, comparing the neural mechanisms involved as participants prepare to attend to the same stimulus feature as on the previous trial (“task-stay” trials) with those required as participants prepare to attend to a different stimulus feature to that previously attended (“task-switch” trials). We wanted to establish how participants maintain or switch attentional set retrospectively, as they attend to features of objects held in visual short-term memory (VSTM). We found that switching, relative to maintaining attentional set retrospectively, was associated with a performance cost, which can be reduced over time. This control process was mirrored by a large parietal and frontal amplitude difference in the event-related brain potentials (ERPs) and significant differences in global field power (GFP) between switch and stay trials. However, when taking into account the switch/stay GFP differences, thereby controlling for this difference in amplitude, we could not distinguish these trial types topographically. By contrast, we found clear topographic differences between preparing an anticipatory feature-based attentional set versus applying it retrospectively within VSTM. These complementary topographical and amplitude analyses suggested that anticipatory and retrospective set control recruited a qualitatively different configuration of underlying neural generators. In contrast, switch/stay differences were largely quantitative, with them differing primarily in terms of amplitude rather than topography

STXBP1 -associated neurodevelopmental disorder: a comparative study of behavioural characteristics

Abstract: Background: De novo loss of function mutations in STXBP1 are a relatively common cause of epilepsy and intellectual disability (ID). However, little is known about the types and severities of behavioural features associated with this genetic diagnosis. Methods: To address this, we collected systematic phenotyping data encompassing neurological, developmental, and behavioural characteristics. Participants were 14 individuals with STXBP1-associated neurodevelopmental disorder, ascertained from clinical genetics and neurology services UK-wide. Data was collected via standardised questionnaires administered to parents at home, supplemented by researcher observations. To isolate discriminating phenotypes, the STXBP1 group was compared to 33 individuals with pathogenic mutations in other ID-associated genes (ID group). To account for the potential impact of global cognitive impairment, a secondary comparison was made to an ability-matched subset of the ID group (low-ability ID group). Results: The STXBP1 group demonstrated impairments across all assessed domains. In comparison to the ID group, the STXBP1 group had more severe global adaptive impairments, fine motor difficulties, and hyperactivity. In comparison to the low-ability ID group, severity of receptive language and social impairments discriminated the STXBP1 group. A striking feature of the STXBP1 group, with reference to both comparison groups, was preservation of social motivation. Conclusions: De novo mutations in STXBP1 are associated with complex and variable neurodevelopmental impairments. Consistent features, which discriminate this disorder from other monogenic causes of ID, are severe language impairment and difficulties managing social interactions, despite strong social motivation. Future work could explore the physiological mechanisms linking motor, speech, and social development in this disorder. Understanding the developmental emergence of behavioural characteristics can help to focus clinical assessment and management after genetic diagnosis, with the long-term aim of improving outcomes for patients and families

Psychopathology and cognitive performance in individuals with membrane-associated guanylate kinase mutations: a functional network phenotyping study.

BACKGROUND: Rare pathogenic variants in membrane-associated guanylate kinase (MAGUK) genes cause intellectual disability (ID) and have recently been associated with neuropsychiatric risk in the non-ID population. However, it is not known whether risk for psychiatric symptoms amongst individuals with ID due to MAGUK gene mutations is higher than expected for the degree of general intellectual impairment, nor whether specific cognitive differences are associated with disruption to this gene functional network. METHODS: This study addresses these two questions via behavioural questionnaires and cognitive testing, applying quantitative methods previously validated in populations with ID. We compared males with X-linked ID caused by mutations in three MAGUK genes (PAK3, DLG3, OPHN1; n = 9) to males with ID caused by mutations in other X chromosome genes (n = 17). Non-parametric and parametric analyses were applied as appropriate to data. RESULTS: Groups did not differ in age, global cognitive impairment, adaptive function or epilepsy prevalence. However, individuals with MAGUK gene mutations demonstrated significantly higher psychopathology risks, comprising elevated total problem behaviours, prominent hyperactivity and elevated scores on an autism screening checklist. Despite these overt difficulties, individuals in the MAGUK group performed more accurately than expected for age and intelligence quotient (IQ) on computerised tests of visual attention, convergent with mouse models of MAGUK loss-of-function. CONCLUSIONS: Our findings support a role for MAGUK genes in influencing cognitive parameters relevant to psychiatric risk. In addition to establishing clear patterns of impairment for this group, our findings highlight the importance of careful phenotyping after genetic diagnosis, showing that gene functional network disruptions can be associated with specific psychopathological risks and cognitive differences within the context of ID.We thank all study participants and their families for extensive contributions to this project. This study was funded by the Academy of Medical Sciences/Wellcome Trust via a Starter Grant for Clinical Lecturers to KB. KB is funded by a National Institute for Health Research Academic Clinical Lectureship. GS is funded by a Wellcome Trust project grant and a James S. McDonnell Foundation Understanding Human Cognition Scholar Award. DEA is funded by an MRC UK intramural programme (MC-A0606-5PQ41). FLR is funded by the National Institute for Health Research (Cambridge Biomedical Research Centre).This is the final version of the article. It first appeared from BioMed Central via http://dx.doi.org/10.1186/s11689-015-9105-

The development of attentional control mechanisms in multisensory environments

Outside the laboratory, people need to pay attention to relevant objects that are typically multisensory, but it remains poorly understood how the underlying neurocognitive mechanisms develop. We investigated when adult-like mechanisms controlling one’s attentional selection of visual and multisensory objects emerge across childhood. Five-, 7-, and 9-year-olds were compared with adults in their performance on a computer game-like multisensory spatial cueing task, while 129-channel EEG was simultaneously recorded. Markers of attentional control were behavioural spatial cueing effects and the N2pc ERP component (analysed traditionally and using a multivariate electrical neuroimaging framework). In behaviour, adult-like visual attentional control was present from age 7 onwards, whereas multisensory control was absent in all children groups. In EEG, multivariate analyses of the activity over the N2pc time-window revealed stable brain activity patterns in children. Adult-like visual-attentional control EEG patterns were present age 7 onwards, while multisensory control activity patterns were found in 9-year-olds (albeit behavioural measures showed no effects). By combining rigorous yet naturalistic paradigms with multivariate signal analyses, we demonstrated that visual attentional control seems to reach an adult-like state at ∼7 years, before adult-like multisensory control, emerging at ∼9 years. These results enrich our understanding of how attention in naturalistic settings develops

Making the Executive ‘Function’ for the Foundations of Mathematics: the Need for Explicit Theories of Change for Early Interventions

A vast body of work highlights executive functions (EFs) as robust correlates of mathematics achievement over the primary and preschool years. Yet, despite such correlational evidence, there is limited evidence that EF interventions yield improvements in early years mathematics. As intervention studies are a powerful tool to move beyond correlation to causality, failures of transfer from executive functions interventions are, we argue, highly problematic for both applied and theoretical reasons. We review the existing correlational and intervention literature at complementary neuroscientific, cognitive, developmental and educational levels. We appraise distinct theories of change underpinning the correlations between EF and early mathematics, as well as explicit or implicit theories of change for different types of EF interventions. We find that isolated EF interventions are less likely to transfer to improvements in mathematics than integrated interventions. Via this conceptual piece, we highlight that the field of EF development is in need of (1) a clearer framework for the mechanisms underpinning the relationships between early EF and other developing domains, such as mathematical cognition; (2) clearer putative theories of change for how interventions of different kinds operate in the context of EF and such domains; (3) and greater clarity on the developmental and educational contexts that influence these causal associations. Our synthesis of the evidence emphasises the need to consider the dynamic development of EFs with co-developing cognitive functions, such as early math skills, when designing education environments

Cross-sectional and longitudinal assessment of cognitive development in Williams syndrome

Williams syndrome (WS) is a rare genetic syndrome. As with all rare syndromes, obtaining adequately powered sample sizes is a challenge. Here we present legacy data from seven UK labs, enabling the characterisation of cross-sectional and longitudinal developmental trajectories of verbal and non-verbal development in the largest sample of individuals with WS to-date. In Study 1, we report cross-sectional data between N = 102 and N = 209 children and adults with WS on measures of verbal and non-verbal ability. In Study 2, we report longitudinal data from N = 17 to N = 54 children and adults with WS who had been tested on at least three timepoints on these measures. Data support the WS characteristic cognitive profile of stronger verbal than non-verbal ability, and shallow developmental progression for both domains. Both cross-sectional and longitudinal data demonstrate steeper rates of development in the child participants than the adolescent and adults in our sample. Cross-sectional data indicate steeper development in verbal than non-verbal ability, and that individual differences in the discrepancy between verbal and non-verbal ability are largely accounted for by level of intellectual functioning. A diverging developmental discrepancy between verbal and non-verbal ability, whilst marginal, is not mirrored statistically in the longitudinal data. Cross-sectional and longitudinal data are discussed with reference to validating cross-sectional developmental patterns using longitudinal data and the importance of individual differences in understanding developmental progression

Cross-sectional and longitudinal assessment of cognitive development in Williams syndrome

Williams syndrome (WS) is a rare genetic syndrome. As with all rare syndromes, obtaining adequately powered sample sizes is a challenge. Here we present legacy data from seven UK labs, enabling the characterisation of cross-sectional and longitudinal developmental trajectories of verbal and non-verbal development in the largest sample of individuals with WS to-date. In Study 1, we report cross-sectional data from between N=102 and N=209 children and adults with WS on measures of verbal and non-verbal ability. In Study 2, we report longitudinal data from N=17 to N=54 children and adults with WS who had been tested on at least three timepoints on these measures. Data support the WS characteristic cognitive profile of stronger verbal than non-verbal ability, and shallow developmental progression for both domains. Both cross-sectional and longitudinal data demonstrate steeper rates of development in the child participants than the adolescent and adults in our sample. Cross-sectional data indicate steeper development in verbal than non-verbal ability, and that individual differences in the discrepancy between verbal and non-verbal ability are largely accounted for by level of intellectual functioning. A diverging developmental discrepancy between verbal and non-verbal ability, whilst marginal, is not mirrored statistically in the longitudinal data. Cross-sectional and longitudinal data are discussed with reference to validating cross-sectional developmental patterns using longitudinal data and the importance of individual differences in understanding developmental progression