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Behaviour across the lifespan and emergent neuropathology - Coggle Diagram
Behaviour across the lifespan and emergent neuropathology
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Population-based study of the prevalence and presentation of dementia in adults with Down’s Syndrome (Holland et al., 2018):
To show the extent of clinical change with age using an established diagnostic instrument in an unbiased, population-based sample of older people with Down’s Syndrome
Age-specific prevalence rates of dementia varied according to the diagnostic criteria used - using the CAMDEX criteria for Alzheimer’s disease, prevalence increased from 3.4-10 to 40% in the 30-39, 40-49 and 50-59 age group
Age related pattern of presentation differs from what is seen in the elderly population, but prevalence is similar 30-40 years earlier in life
Lifespan trajectory of affect in Cornelia de Lange syndrome: Towards a neurobiological hypothesis (Groves et al., 2019) -
Depressive symptomatology and low affect are comparatively common in individuals with genetic disorders like CdLS - however, lifespan trajectories and associated person characteristics have not been assessed
--> Compared to FXS of chronological age and total number of behaviour indicators for ASD included
7 year longitudinal study of affect was conducted in individuals with CdLS - trajectories were explored
CdLS group were lower in mood than the FXS group overall - interest rates showed decline over the lifespan
They are a group more at risk of decline in levels of interest and pleasure, which FXS children do not show
Six developmental trajectories characterise children with autism (Fountain et al., 2012) -
Longitudinal study - evaluative items for social, communication and repetitive behaviour functioning
Six typical patterns identified - significant heterogeneity in developmental pathways
--> Children whose symptoms were least severe at first improve more rapidly than those severely affected
--> One group experienced rapid gains, moving from severely affected to high functioning
--> Socioeconomic factors were correlated - children with non-Hispanic, white, well educated mothers more likely to be high functioning, and minority children with less-educated mothers or intellectual disabilities were unlikely to experience rapid gains
A prospective 20-year longitudinal follow-up of dementia in with Down Syndrome (McCarron et al., 2017) -
Over a 20 year period, 97.4% of participants developed dementia with a mean age of dementia diagnosis being 55 years old
Clinical dementia associated with cognitive and function decline and seizure activity
Dementia risk increased from 23% in those aged 50 years to 80% in those aged 65 years and above
No differences by level of ID
Neurodevelopmental disorders - research challenges and solutions (Riby et al., 2015)
Chapter 2: Why development matters:
Essential to understand change over the lifespan to understand how different developmental factors interact e.g. a delay at Time 2 may have been crucial, but something else which was important at time 2 was not important by Time 5
Adult neuropsychological models therefore inadequately explain the dynamic change in neurodevelopmental disorders
--> For example, there is debate over why the fusiform facial area is so large in WS - could be that a larger FFA leads to better performance in facial recognition tasks, or that the orientation towards faces in infancy could lead to a large FFA (bidirectional)
--> Have to observe developmentally and longitudinally
--> Could also be that a fascination with voices due to the auditory input in utero that prompts this relationship
--> Crucial to trace double dissociation back to early years to understand if it is the case
Mapping genotype to phenotype - FXS is an example of how a single gene mutation has a range of cascading effects due to the nature of the protein expressed
Additionally, DS usually results in late development of the hippocampus and the prefrontal cortex, and thus developmental approaches have to be used as this is a different trajectory to controls
Leads to cognitive phenotype of poor episodic and spatial memory, but not working and implicit memory processes - however, Rast and Meltzoff (1995) found that two-year-olds with DS have intact episodic memory relative to how they have acquired object permanence
Early investigation allows better understanding of the developmental trajectory - have to understand how a phenotype develops from Time 1 to Time 6 (for example) to illustrate the cognitive phenotype, and how this compares to other syndromes
Cognition - WS has skilled language, face proficiency and social motivation, but low numerical and spatial cognition
However, the brain in WS fails to become progressively specialised, as the TD brain initially processes incoming input bilaterally, but with development localisation and specialisation occurs
However, processing remains bilateral in WS - they have the same temporal signature for faces, cars and other objects
Therefore, the proficiency is due to other mechanisms to TD brains
High-level cognition should be mapped onto basic skills in infancy:
Approximation - TD individuals are able to discriminate between small number ratios and large number ratios in a sequential development pattern, but WS individuals can only perform to the same level of small number discrimination tasks, whereas DS infants perform better with discrimination of large number approximation
Suggests a double dissociation, as one system can be impacted where the other is not - however, this is adult neuropsychological language, and thus it may be that systems become emergent over time through interactions
Tested eye movement and attention as a potential mechanism in this difference - in WS, it appears that deficit in rapid saccade planning (shifting) leads to difficulty in dealing with large arrays, whereas DS individuals are better at scanning, but have difficulty in sustained attention and thus cannot identify small displays
Therefore, attention shifting and sustainment is the mechanism, not a double dissociation of numerical specialisation, as better shifting helps with large scale number arrays, and sustained attention is involved in small numbers
Basic-level deficiencies and proficiencies rather than high level specialised dissociation
The environment -
Impact of low SES - exposure to abuse, lack of support, many of those studied are from high SES families with caring environments
The moment a parent is informed that their child has a genetic disorder, their behaviour subtly adapts - therefore, there is an epigenetic effect
Even in TD, the environment can impact cognitive development
In TD cases, overgeneralisation of labels when learning language, crawling and exploration and using the mouth to explore is allowed, which helps with linguistic and social development
--> But in neurodevelopmental disorders, parents sometimes overcorrect generalisation and are more anxious about them exploring, which hinders their linguistic and social development - impaired categorising is common in NDCs, possibly due to parental fear about low IQ
Chapter 7: Variability in NDCs - evidence from ASD
ASD is highly heterogeneous and variable in aetiology and phenotype
Main areas of deficit are social communication and repetition / sensory behaviours (triad -> dyad)
Although there is reliability across diagnostic criteria, there is little biological validity - Research Domain Criteria is used to connect behaviour and cognitive systems to neurobiological and genetic predispositions - aims to look at intervention over a single treatment
Causes and prevalence -
ASD is highly heritable, but prenatal factors may have a larger role than previously thought
Genetic factors - complex, involve rare chromosomal abnormalities, several genes have an impact - have an impact on neural functioning which underlies the behavioural phenotype
Affects approximately 1 in 100 individuals, or up to 2% of the population
--> Depending on the diagnostic criteria used and the narrowness of assessment, prevalence can differ by a factor of 4 between narrow and broad case analysis
--> Higher prevalence due to changing diagnostic criteria, investigation in individuals who would have been previously excluded e.g. high IQ and ADHD diagnosis
Considered an NDC because there is variability within individuals over time - high stability in traits however
Was previously debate about optimal outcomes and whether it is a lifetime condition, as early diagnosis means intervention and support
Clinical certainty with behavioural disorders is fragile - measurement accuracy and reliability can impact the stability of diagnosis
Cognitive and behavioural phenotypes -
Used to be considered that intellectual disability was key to diagnosing autism - now, only 50% have a co-occurring intellectual disorder
More likely to show peaks and troughs in different areas of learning, theory of mind, linguistic ability and behaviour
Language and communication -
Language onset and outcomes are highly variable - older estimations were based on intellectually disabled populations of ASD, and thus current estimations of outcomes are more positive
Typical for them to be nonverbal at ages 2-3 - severity of symptoms at this age was a strong predictor for outcomes of language at 9, along with joint attention and non-verbal cognitive abilities
Large variability within ASD, and ASD had variation compared to PDD-NOS
Large variability between effects on receptive and expressive language - however, receptive does seem to be more delayed than expressive, and thus intervention should help to promote understanding in social communication
Developmental trajectories:
ASD individuals have challenges in NT world due to social communication limitations, rigid and repetitive thinking and behaving
Study of siblings at risk for ASD - trajectories of those who go on to be diagnosed diverge, with developmental slowing along a range of domains
Demographic variables can also impact trajectory (ethnicity and parental education)
However, not all children respond to intervention and outcomes can still be poor
Variability in adult outcome:
Although diagnosis remains stable symptoms do improve over time
However, proportions of individuals living independently and being in work are low, and care needs can still be high
In the minority that had IQs greater than 70 had poor outcomes, with severe behavioural difficulties and epilepsy
Some adults can plateau in adaptive skills after an increase in adolescence - could be due to removal of supportive environments, but highlights the need for ongoing community services for those with ASD
Co-occurring mental health should be planned for as well as assessed
Other studies indicate a more positive picture - however, Farley et al (2009) used a sample of ‘high functioning’ individuals, who were attached to a church community which provided educational, social and occupational support
Subtypes - hard to define due to how heterogeneous it is:
Attempting to do this based on biological syndromes with known aetiology is also difficult as they do not neatly map onto cognitive and behavioural phenotypes - still variability in biological syndromes with higher ASD prevalence
Grouping based on behavioural subtypes may be more impactful
Cognitive subgroups would allow for more targeted intervention, and identifying strengths could lead to bootstrapping or overcoming difference
Attempts to define with sensory modality (auditory) and comparison to ADHD, but variability is too high
Heterogeneity as noise -
Almost always overlap between TD and ASD groups as variation in the ASD population is higher than the TD population
Investigating the way in which cognitive systems are differently ‘set' or ‘tuned’, rather than an all or none approach
Other strengths can compensate for differences in different ways
Larger samples are also needed to find subgroups and lighten the effects of heterogeneity
Behaviour across the lifespan in Cornelia de Lange Syndrome - Groves, Oliver & Moss (2021):
Poorer psychological wellbeing is more common in older individuals than younger individuals
Suggested critical period of change from 15-22 years old - behaviour appears to stabilise into adulthood
-> Reported change in autistic characteristics and anxiety
-> Older individuals show more autistic characteristics, such as social impairment, greater need for sameness, and less interest and pleasure compared to younger individuals
-> Mood remains stable
Cognitive cause - Greater EF deficits, specifically in verbal memory:
Hard to keep pace with planning and social interactions with age as a result of this
Decrease in capacity with age could lead to anxiety and preference for sameness / autism characteristics
Lessens cognitive load to follow routine and sameness, and also cause withdrawal from activities that place too much load on individuals
Intolerance of newness due to the amount of information that has to be processed
Increased uncertainty around newness leads to low mood and anxiety
Biological cause - Possibility of neurodegeneration in some mutations of CdLS, leading to the behavioural changes witnessed
Environmental cause - need for transitional care:
Change to schooling environment - loss of predictable structure and routine in college years or adult learning facilities
Uncertainty around living and skills associated with this - unpredictability leads to lower mood and loss of pleasure
Greater demand as an adult - reduced capacity to cope and provide explanation for changes
Greater presence of autism characteristics could be due to the use of sameness and routine as a coping strategy
However, language improves and adaptive skills remain stable despite age - change described is highly specific and not global ability decline:
Emergent biological and cognitive vulnerabilities, coupled with increased autism characteristics, intolerance of uncertainty and anxiety which are often unrecognised and untreated, leads to reduced capacity to cope with significant change