Neuroscience of Developmental Disorders
Developmental Disorders
Disorders resulting from atypical or delayed mental or physical development, or developmental delays
Models of Developmental DIsorders
Medical model: a model that takes a deficit view through measuring individuals against the norm
Social model: a model that looks at changing systems and support in society, through distinguishing between an impairment and a disability
Studying Developmental Disorders
Key concepts needed to study developmental disorders
The use of typical development as context
The idea that development is a process
Key developmental timings
The use of multiple methods needed to study the various elements
methods of studying developmental disorders
Cross sectional studies
Age based
Where people are matched according to their actual or developmental ages
Group based
Longitudinal studies
Intervention studies
Where people are compared between different groups e.g. ASD and controls
Studying the same small group of individuals over a long period of time
Also known as randomised control studies
Causal models of developmental disorders
Behavioural: what is observed about behaviours
Cognitive: a mental component (“level of mind”) that is implied through behavioural and biological evidence
Biological: what is observed about the brain, genes, and internal phenomena
Developmental Language Disorder (DLD)
A developmental disorder specific to language that affects roughly 7% of preschoolers
Involves poor vocabulary, grammar and phonology
However has typical peripheral hearing and oral motor functioning
Theories of DLD
Cognitive theories: suggest information processing limitations (both generally and specific e.g. phonological and auditory temporal deficits
Behavioural theories: specific deficits in grammar
Biological theories: Procedural Deficit Hypothesis
Suggests that there are two components to Long Term Memory
Procedural: involves the basal ganglia, frontal cortex and cerebellum, and relates to motor, perceptual and cognitive skills
Declarative: involves the hippocampus and medial temporal lobes, and relates to learning arbitrary associations
Deficits here can lead to issues with syntax and phonology
Deficits here can lead to vocabulary and nonverbal learning issues
Neurocognitive evidence for DLD
Language Network: areas of the brain involved in language, such as Broca’s area, Wernicke’s area, inferior frontal gyrus and parietal cortex
Structural differences such as reduced myelination found in the inferior frontal gyrus and striatum
Atypical structural lateralisation found due to lack of asymmetry in the Perisylvian cortex
Atypical functional lateralisation in the left hemisphere
Memory network: areas of the brain involved in procedural and declarative memory such as the basal ganglia, cerebellum, hippocampus and medial temporal lobes
EEG evidence suggests atypical language and speech processing in these regions in DLD vs controls
Dyslexia
Patterns of learning difficulties relating to issues with accurate word recognition, poor decoding and poor spelling
Issues with reading arise from poor decoding abilities (the ability to identify words) rather than comprehension (ability to understand meanings)
Theories of Dyslexia
Sensory theories
Rapid auditory processing theory: key deficit involves issues processing short and rapidly varying sounds
Rise Time Theory: key deficit involves issues with rise times (the time taken from sound onset to peak pitch/amplitude
Visuo/magnocellular theory: key deficit involves issues processing rapid changes in visual information
Cerebellar theory: dyslexics have a dysfunctional cerebellum that causes dysfunction in motor control and automisation
Phonological Deficit Hypothesis
These theories have limited evidence to support their existence or evidence as to identify the primary deficit of sylexia
A theory that suggests that the core deficits involved in dyslexia are with phonological coding deficits, as well as other broader language difficulties
Implicit phonology: unconscious use of language sounds
explicit phonology: conscious use of language sounds, often most impaired in dyslexia and evidenced through phoneme deletion tasks
Neurological Evidence for Dyslexia
this theory can be evidenced by dyslexics performing worse on nonword repetition accuracy tests
Reading Network
a network of brain areas involved in reading decoding and comprehension
left inferior frontal gyrus
left inferior parietal lobe
occipitotemporal cortex
there is fMRI evidence of dyslexics having low activity in the left inferior parietal lobe and occipitotemporal lobe vs controls
however dyslexics were found to have increased activity in the left inferior frontal gyrus, which was seen as over compensatory
there is also evidence that the Visual Wordform Area in the occipitotemporal lobe has disrupted connections with the inferior parietal language areas compared to controls
neurological evidence has been found across different languages such as English, German and Italian
helps improve the generalisability of the results
Autism Spectrum Disorder (ASD)
a developmental disorder which involves impairments to social communication and reciprocity, with rigid and restricted behaviours and interests
Dyad of Impairment
Impairments to social communication and interaction
restricted repetitive patterns of behaviour
theories of ASD
at aged 12-24mo it can be evidenced by reduced typical social interest, atypical language development and lack of coordination of gaze and gesture
social deficit theories
Theory of Mind
the unconscious ability to attribute mental states to oneself and others, and to recognise that others may have different beliefs, intentions and desires to oneself
aims to explain the entire triad (dyad) of impairment
evidence for impairments
Sally Anne Task
a girl places a ball on a table and leaves, another girl puts the ball in the box,, when girl 1 comes back where does she first look for the ball
50% correct at aged 4 for neurotypicals, however this is almost double for ASD (9.2yrs)
Mind in the Eye Task
people shown pictures of eyes and asked which of the two provided adjectives best describe the eyes
ASDs perform better than chance but worse than neurotypicals
however scores usually improve when the eyes are moving or when they are shown in context of the whole face
Implicit Mental State Task
participants shown a video of shapes moving around an area in a socially meaningful way and asked to describe the movement
ASDs describe the movements using spatial and geometric properties vs neurotypicals who use human emotions and descriptors
Neurological evidence
The Social Brain
areas of the brain thought to be involved in social tasks and interactions
medial prefrontal cortex
anterior cingulate cortex
amygdala
inferior frontal gyrus
temporal parietal junction
fMRI evidence showed that there is a lack of activation in frontal lobe regions and amygdala, however there is also increased temporal lobe activation
Mirror Neuron System
a brain system that works with the social brain to help with our understanding of others' emotions
fMRI evidence shows increased activity in the right visual and left parietal areas, and less activity in the insula and amygdala than controls, with no mirror neuron activity in the pars opercularis
Impaired Social Perception Theory
a theory that suggests that many observed social differences of ASD are linked to low level social perception differences in infancy, which impact the development of social cognition
at risk samples who went on to develop ASD showed little to no response difference in ERP recordings to the 'look toward' vs the 'look away' conditions
weak central coherence theory
the idea that processing differences are seen across a range of different domains not just social communication
Attention Deficit Hyperactivity Disorder (ADHD)
A developmental disorder characterised by inattention and/or hyperactivity/impulsivity
Hyperactivity
restless and fidgety
difficulty planning
excessive talking and 'blurting out'
difficulty awaiting turn
inattention
difficulty sustaining attention
difficulty organising tasks
easily distracted
often misplacing or losing items
diagnosis
Conners Continuous performance test (respond to targets and ignore nontargets
characterised by higher than average misses and commission errors (e.g. false alarms and anticipatory responses)
diagnosis is often difficult due to the subjective criteria and symptom overlap with other conditions such as OCD and GAD
EEGs can be used with up to 90% accuracy in diagnosis, however it is not fully standardised nor checked for reliability/validity
Neurocognitive theories of ADHD
executive dysfunction theory
delay aversion theory
dual deficit theory
weakness in one of the areas relating to top-down cognitive processes that facilitate goal oriented decision making
brain areas involved include the ventral/medial prefrontal cortex, anterior cingulate cortex, and dorsolateral prefrontal cortex
Barkley's model of behavioural inhibition
inhibition is a prerequisite for executive function skills that underpin motor control. leading to issues in areas such as working memory, self control and emotional regulation
measures of executive dysfunction
Vigilance (sustained attention)
Planning (Tower of Hanoi)
Response inhibition (stop signal reaction time)
participants asked to press a button when they see a cross, but not to if a beep is played at the same time
sequence of letters shown for 15 minutes and asked to press a button when a target sequence occurs (e.g. F occurs after R)
measured through omission and commission errors
asked to move a stack of objects from one place to another in the fewest possible moves
Neurobioloigcal evidence
reduced grey matter volume in the fronto-striatal circuit linked to regulation of executive function
atypical white matter tracts in fronto-striatal, fronto-posterior, interhemisphere and cerebellar regions
a theory suggesting that ADHDers will choose immediate small rewards over delayed larger rewards due to poor delay gratification
with this view it suggests that the condition is more of an affective disorder (affecting the way you think and feel)
reward network
suggests that there are differences in the processing throughout this network
a brain system involved in reward circuits
frontal and parietal cortex
supplementary motor cortex
nucleus accumbens
thalamus
basal ganglia
cerebellum
children with ADHD more likely to choose 1 point in 2 seconds over 2 points in 30seconds (Sonuga Barke et al 1992)
a model that looks at the brain deficits involved in inattentive and hyperactive ADHD subtypes
The most common deficit in inattentive subtypes involves a dysfunction of the dorsolateral prefrontal cortex
the delay aversion deficit is most commonly associated with hyperactive subtypes