Understanding attention, memory and social biases in fragile X syndrome: Going below the surface with a multi-method approach

Adaptive group behavior of Fragile X mice in unfamiliar environments

Fragile X Syndrome (FXS) stands out as a prominent cause of inherited intellectual disability and a prevalent disorder closely linked to autism. FXS is characterized by substantial alterations in social behavior, encompassing social withdrawal, avoidance of eye contact, heightened social anxiety, increased arousal levels, language deficits, and challenges in regulating emotions. Conventional behavioral assessments primarily focus on short-term interactions within controlled settings. In this study, we conducted a comprehensive examination of the adaptive group behavior of Fmr1 KO male mice over a three-day period, without introducing experimental interventions or task-based evaluations. The data unveiled intricate behavioral anomalies, with the most significant changes manifesting during the initial adaptation to unfamiliar environments. Notably, certain behaviors exhibited a gradual return to typical patterns over time. This dynamic Fmr1 KO phenotype exhibited heightened activity, featuring increased exploration, amplified social interest, and an unconventional approach to social interactions characterized by a higher frequency of shorter engagements. These findings contribute to the growing understanding of social behavior in individuals with FXS and underscore the significance of comprehending their adaptive responses in various environmental contexts.

Visual attention patterns during a gaze following task in neurogenetic syndromes associated with unique profiles of autistic traits: Fragile X and Cornelia de Lange syndromes

BACKGROUND

Gaze following difficulties are considered an early marker of autism, thought likely to cumulatively impact the development of social cognition, language and social skills. Subtle differences in gaze following abilities may contribute to the diverse range social and communicative autistic characteristics observed across people with genetic syndromes, such as Cornelia de Lange (CdLS) and fragile X (FXS) syndromes.

AIMS

To compare profiles of 1) visual attention to the eye region at critical points of the attention direction process, 2) whether children follow the gaze cue to the object, and 3) participant looking time to the target object following the gaze cue between groups and conditions.

MATERIALS AND METHODS

Children with CdLS (N = 11) and FXS (N = 8) and autistic (N = 22) and neurotypical (N = 15) children took part in a passive viewing paradigm adapted from Senju and Csibra (2008), in which videos of a central cue (ball/cartoon face/human face) directed attention towards one of two objects. Visual attention patterns were recorded via eye tracking technology.

RESULTS

Neurotypical children were used as a reference group against which the autistic, CdLS and FXS groups were compared. Although autistic children looked at the eye region for significantly less time, they looked at the target object as frequently and for a similar duration as neurotypical children. Children with FXS looked at the target as frequently as neurotypical children but looked at it for comparatively less time. Both neurotypical children and children with CdLS frequently looked at the eye region, but children with CdLS were less likely to look at the target than neurotypical children.

CONCLUSIONS

Findings provide preliminary evidence of unique patterns of visual attention and gaze following strategies in children with CdLS, children with FXS and autistic children. These unique gaze following patterns may underpin the distinct profiles of social and communication autistic traits observed between these groups.

A holistic approach to fragile X syndrome integrated guidance for person-centred care

BACKGROUND

The Fragile X community has expressed a desire for centralised, national guidelines in the form of integrated guidance for Fragile X Syndrome (FXS).

METHODS

This article draws on existing literature reviews, primary research and clinical trials on FXS, a Fragile X Society conference workshop and first-hand experience of clinicians who have worked with those living with FXS over many years.

RESULTS

The article scopes proposed integrated guidance over the life course, including appendices of symptoms, comorbidities and referral options for FXS and Fragile X Premutation Associated Conditions.

CONCLUSION

Integrated guidance would provide an authoritative source for doctors, health professionals, therapists, care workers, social workers, educators, employers, families and those living with FXS, so that a holistic, person-centred approach can be taken across the United Kingdom to garner the best outcomes for those with FXS.

Noise-induced hearing loss reduces inhibitory neurotransmitter synthesis in ventral hippocampus and contributes to the social memory deficits of mice

Despite affecting over 1.5 billion people globally, hearing loss (HL) has been referred to as an "invisible disability", with noise exposure being a major causative factor. Accumulating evidence suggests that HL can induce cognitive impairment. However, relatively little is known about the effects of noise-induced hearing loss (NIHL) on social memory. This study aimed to further investigate the effect of NIHL on social behaviours in mice. We established a rodent model of NIHL using 4-week-old C57BL/6J mice who experienced narrow noise exposure at 116 dB for 3 h per day over two consecutive days. Hearing ability was subsequently evaluated through auditory brainstem response (ABR) testing, and potential changes in the morphology of cochlear hair cells were assessed using immunofluorescence. The sociability and social memory of the mice were evaluated using the three-chamber social interaction test. Noise exposure resulted in complete and persistent HL in C57BL/6J mice, accompanied by severe loss of cochlear hair cells. More importantly, social memory was impaired in adult NIHL mice, whereas their sociability remained intact, these changes were accompanied by a decrease in the protein levels of the inhibitory neuron marker glutamic acid decarboxylase 67 (GAD67) in the ventral hippocampus. This study is the first to confirm that long-term auditory deprivation from HL induced by noise exposure results in social memory deficits in mice without altering their sociability.

The use of eye-tracking technology as a tool to evaluate social cognition in people with an intellectual disability: a systematic review and meta-analysis

BACKGROUND

Relatively little is known about social cognition in people with intellectual disability (ID), and how this may support understanding of co-occurring autism. A limitation of previous research is that traditional social-cognitive tasks place a demand on domain-general cognition and language abilities. These tasks are not suitable for people with ID and lack the sensitivity to detect subtle social-cognitive processes. In autism research, eye-tracking technology has offered an effective method of evaluating social cognition-indicating associations between visual social attention and autism characteristics. The present systematic review synthesised research which has used eye-tracking technology to study social cognition in ID. A meta-analysis was used to explore whether visual attention on socially salient regions (SSRs) of stimuli during these tasks correlated with degree of autism characteristics presented on clinical assessment tools.

METHOD

Searches were conducted using four databases, research mailing lists, and citation tracking. Following in-depth screening and exclusion of studies with low methodological quality, 49 articles were included in the review. A correlational meta-analysis was run on Pearson's r values obtained from twelve studies, reporting the relationship between visual attention on SSRs and autism characteristics.

RESULTS AND CONCLUSIONS

Eye-tracking technology was used to measure different social-cognitive abilities across a range of syndromic and non-syndromic ID groups. Restricted scan paths and eye-region avoidance appeared to impact people's ability to make explicit inferences about mental states and social cues. Readiness to attend to social stimuli also varied depending on social content and degree of familiarity. A meta-analysis using a random effects model revealed a significant negative correlation (r = -.28, [95% CI -.47, -.08]) between visual attention on SSRs and autism characteristics across ID groups. Together, these findings highlight how eye-tracking can be used as an accessible tool to measure more subtle social-cognitive processes, which appear to reflect variability in observable behaviour. Further research is needed to be able to explore additional covariates (e.g. ID severity, ADHD, anxiety) which may be related to visual attention on SSRs, to different degrees within syndromic and non-syndromic ID groups, in order to determine the specificity of the association with autism characteristics.

Understanding perceptual decisions by studying development and neurodiversity

A cornerstone of human information processing is how we make decisions about incoming sensory percepts. Much of psychological science has focused on understanding how these judgements operate in skilled adult observers. While not typically the focus of this research, there is considerable variability in how adults make these judgements. Here, we review complementary computational modelling, electrophysiological data, eye-tracking and longitudinal approaches to the study of perceptual decisions across neurotypical development and in neurodivergent individuals. These data highlight multiple parameters and temporal dynamics feeding into how we become skilled adult perceptual decision makers, and which may help explain why we vary so much in how we make perceptual decisions.

Re-visiting the 'mysterious myth of attention deficit': A systematic review of the recent evidence

Based on the inclusive and methodologically rigorous framework provided by Ed Zigler's developmental approach, we previously challenged what we called, 'the mysterious myth of attention deficit', the fallacy of attention as a universal deficit among persons with intellectual disability (ID). In this latest update, we conducted a systematic review of studies of essential components of attention among persons with ID published in the interim since the last iteration of the mysterious myth narrative was submitted for publication approximately a decade ago. We searched the databases PubMed and PsycINFO for English-language peer-reviewed studies published from 1 January 2011 through 5 February 2021. In keeping with the developmental approach, the two essential methodological criteria were that the groups of persons with ID were aetiologically homogeneous and that the comparisons with persons with average IQs (or with available norms) were based on an appropriate index of developmental level, or mental age. Stringent use of these criteria for inclusion served to control for bias in article selection. Articles were then categorised based on aetiological group studied and component of visual attention. Based on these criteria, 18 articles were selected for inclusion out of the 2837 that were identified. The included studies involved 547 participants: 201 participants with Down syndrome, 214 participants with Williams syndrome and 132 participants with fragile X syndrome. The findings from these articles call attention to the complexities and nuances in understanding attentional functioning across homogeneous aetiological groups and highlight that functioning must be considered in relation to aetiology; factors associated with the individual, such as developmental level, motivation, styles and biases; and factors associated with both the task, such as context, focus, social and emotional implications, and levels of environmental complexity.

fmr1 Mutation Alters the Early Development of Sensory Coding and Hunting and Social Behaviors in Larval Zebrafish

Autism spectrum disorders (ASDs) are developmental in origin; however, little is known about how they affect the early development of behavior and sensory coding. The most common inherited form of autism is Fragile X syndrome (FXS), caused by a mutation in FMR1 Mutation of fmr1 in zebrafish causes anxiety-like behavior, hyperactivity, and hypersensitivity in auditory and visual processing. Here, we show that zebrafish fmr1-/- mutant larvae of either sex also display changes in hunting behavior, tectal coding, and social interaction. During hunting, they were less successful at catching prey and displayed altered behavioral sequences. In the tectum, representations of prey-like stimuli were more diffuse and had higher dimensionality. In a social behavioral assay, they spent more time observing a conspecific but responded more slowly to social cues. However, when given a choice of rearing environment fmr1-/- larvae preferred one with reduced visual stimulation, and rearing them in this environment reduced genotype-specific effects on tectal excitability. Together, these results shed new light on how fmr1-/- changes the early development of neural systems and behavior in a vertebrate.SIGNIFICANCE STATEMENT Autism spectrum disorders (ASDs) are caused by changes in early neural development. Animal models of ASDs offer the opportunity to study these developmental processes in greater detail than in humans. Here, we found that a zebrafish mutant for a gene which in humans causes one type of ASD showed early alterations in hunting behavior, social behavior, and how visual stimuli are represented in the brain. However, we also found that mutant fish preferred reduced visual stimulation, and rearing them in this environment reduced alterations in neural activity patterns. These results suggest interesting new directions for using zebrafish as a model to study the development of brain and behavior in ASDs, and how the impact of ASDs could potentially be reduced.

A Novel Mechanism for T1R-Independent Taste Responses to Concentrated Sugars

Recent findings from our laboratory demonstrated that the rostral nucleus of the solitary tract (rNST) retains some responsiveness to sugars in double-knock-out mice lacking either the T1R1+T1R3 (KO1+3) or T1R2+T1R3 (KO2+3) taste receptor heterodimers. Here, we extended these findings in the parabrachial nucleus (PBN) of male and female KO1+3 mice using warm stimuli to optimize sugar responses and employing additional concentrations and pharmacological agents to probe mechanisms. PBN T1R-independent sugar responses, including those to concentrated glucose, were more evident than in rNST. Similar to the NST, there were no "sugar-best" neurons in KO1+3 mice. Nevertheless, 1000 mm glucose activated nearly 55% of PBN neurons, with responses usually occurring in neurons that also displayed acid and amiloride-insensitive NaCl responses. In wild-type (WT) mice, concentrated sugars activated the same electrolyte-sensitive neurons but also "sugar-best" cells. Regardless of genotype, phlorizin, an inhibitor of the sodium-glucose co-transporter (SGLT), a component of a hypothesized alternate glucose-sensing mechanism, did not diminish responses to 1000 mm glucose. The efficacy of concentrated sugars for driving neurons broadly responsive to electrolytes implied an origin from Type III taste bud cells. To test this, we used the carbonic anhydrase (CA) inhibitor dorzolamide (DRZ), previously shown to inhibit amiloride-insensitive sodium responses arising from Type III taste bud cells. Dorzolamide had no effect on sugar-elicited responses in WT sugar-best PBN neurons but strongly suppressed them in WT and KO1+3 electrolyte-generalist neurons. These findings suggest a novel T1R-independent mechanism for hyperosmotic sugars, involving a CA-dependent mechanism in Type III taste bud cells.SIGNIFICANCE STATEMENT Since the discovery of Tas1r receptors for sugars and artificial sweeteners, evidence has accrued that mice lacking these receptors maintain some behavioral, physiological, and neural responsiveness to sugars. But the substrate(s) has remained elusive. Here, we recorded from parabrachial nucleus (PBN) taste neurons and identified T1R-independent responses to hyperosmotic sugars dependent on carbonic anhydrase (CA) and occurring primarily in neurons broadly responsive to NaCl and acid, implying an origin from Type III taste bud cells. The effectiveness of different sugars in driving these T1R-independent responses did not correlate with their efficacy in driving licking, suggesting they evoke a nonsweet sensation. Nevertheless, these salient responses are likely to comprise an adequate cue for learned preferences that occur in the absence of T1R receptors.

Developmental Perspectives on the Study of Persons with Intellectual Disability

Developmental approaches provide inclusive, universal, and methodologically rigorous frameworks for studying persons with intellectual disability (ID). This is an exceptionally heterogeneous group with regard to etiology, genotype, and phenotype that simply shares the traditional diagnostic criteria, typically a score of two standard deviations below the population mean of 100 on standardized IQ tests and deficits in adaptive behavior. We trace the foundational, conceptual, and methodological roots of developmental approaches and highlight ways that these and more recent iterations continue to be central to advances in the increasingly nuanced study of persons with ID. This work is premised on the consideration of specific etiological groupings and subgroupings across and between different domains of functioning within the context of familial and complex environments throughout the life span. We highlight the potential contributions of advances in behavioral methodologies, genomics, and neuroscience when considered within universal and hierarchic frameworks based on development.