Session Thirteen (Brain Development and ADHD) Flashcards
Outline how the brain normally develops, from childhood into adulthood?
Two main processes:
- Linear INCREASE in white matter, peaks at age 35
- Grey matter highest in childhood, then DECREASE into adolescence and adulthood.
- Loss of grey matter is regressive and progressive; occurs due to connections which are being used a lot becoming reinforced and those that aren’t dying out
- Termed “Synaptic Pruning”
- Changes most aggressively in adolescence.
These two processes are regionally and temporally heterogenous, different things happening in different areas at different times
How does white matter increase?
Increase in:
- Myelinated axons
- Axonal diameter
- Glial cells
What is grey matter an indirect measure of?
- Cell bodies
- Dendrites
- Vasculature
- Synapses
- Extracellular space
These are the things that die off in synaptic pruning
What are the general patterns of brain development, in terms of which areas develop first/last?
- Posterior to anterior
- Inferior to superior
- Central to peripheral
Which areas develop earliest is related to maturation of relevant cognitive functions and functional networks:
- First area to develop = Primary sensory cortex.
- Last area to develop = Areas associated with higher level association
Interestingly, last areas to mature become first areas to atrophy in old age.
How does the brain age from late adulthood onwards?
- Grey matter mostly stables out, some small loss continues
- White matter begins to drop off once more
- Leads to the cognitive decline we see in all older people
- Dementia is an acceleration of this process
Who’s brains develop faster, males or females?
Females. This is potentially why we see more brain developmental issues in boys.
Specifically, the cerebellum and basal ganglia both finish developing significantly earlier in girls.
Which areas of the brain are known to be fully developed by age 10?
Limbic areas e.g. hippocampus and amygdala (crucial to emotional response and fear).
HOWEVER regions which exert an amount of control over this area are not fully developed at this point, meaning children and adolescents remain emotionally unstable
What are the 3 main Fronto-Striato-Cerebellar circuits?
Affective, Cognitive, Motor
Outline White Matter Tract Development?
Prominent increases:
- 0-3 months
- 4 years
- Steeply into adolescence
- Increase into adulthood gradually
- Decreased growth till mid-adulthood
Briefly summarise the life span perspective of brain development?
WM:
- Non-linear increase until adulthood
- Plateau in mid adulthood
- Decrease during ageing after 50
- Latest peaks occur in front-temporal areas
GM:
- Curvi-linear increase in GM
- Increase in adolescence
- Later decrease
- Further decrease after age 50
Sex difference findings are not consistent
What is thought to be a crucial factor explaining the cognitive development of children?
Changes in ratio of white to grey matter
What are the ‘hot’ and ‘cold’ aspects of executive function?
Cold = functions that subserve mature, adult goal-directed behaviours e.g.
- Cognitive control (motor and interference inhibition, attention switching)
- Attention (sustained attention, selective and divided attention)
- Working memory
Hot = functions that involve some sort of reward
- Motivation control
- Reward related decision making
Outline the different Cognitive control functions (part of cold EF) and how they are tested for?
Motor response inhibition = the ability to inhibit a prepotent motor response
- Go and no-go task
- Stop task
Interference inhibition = the ability to inhibit a prepotent tendency to respond to an interfering stimulus
- Simon task
- Eriksen Flanker task
Cognitive flexibility = the ability to inhibit a response that is no longer appropriate and re-engage with a new response
- Wisconsin card sorting task
How can working memory (a facet of cold EF) be tested clinically?
N-back tests.
- Sequence of slides
- Participant has to, when prompted, state what was on the slide 1 or 2 slides ago.
Why is the development of cold Executive functions so important?
Prevents mind-wandering, essential to engagement in goal directed activity.
If lagging at risk of disorders such as ADD.
Outline findings from task-based fMRI studies into how our brains develop functionally?
- We see progressively increased activation in task-relevant regions and networks as we age
- In particular in the fronto-cortical, portico-striatal and portico-cerebellar networks
- Children exhibit more diffuse activation in non-specialised areas
- Progressively better inter-regional connectivity between task-relevant regions with age.
Outline findings from resting-state fMRI studies into how our brains develop functionally?
- Progressively more interconnected default mode network with age
- Progressively more switching off of the DMN during tasks
- Shift from local to distributed network architecture (short range connections decrease, long range ones increase) with age
- Highly connected regions begin to connect more with other highly connected regions as we age into adulthood.
- Inter-hemispheric connectivity increases
What did Rubia eat al, 2007, show about frontalisation?
- Ps aged 10-43
- Activation in the brain’s inhibitory mechanisms (the IFG, Caudate, Thalamus, Cerebellum) increases
- Children showed more diffuse activation, in adults this activation became far more focussed
- As activation increased, so did performance on a Stop task
- Fronto-striatal networks increase with age
What this essentially means:
- As we age, we become more able to activate crucial areas of the brain associated with executive function and behavioural inhibition
- Making us more capable of inhibiting an automatic response and producing a correct response
- Ability to monitor performance increases
What have studies shown about the development of working memory?
Andre et al, 2010, meta-analysis of 10 studies into the development of Working memory in adolescents found:
- Increases in areas related to working memory
- Decreases in areas not relevant to WM or in Default Mode Network
- You see decreases in compensatory or supportive regions
What studies have been performed into Hot EF functions?
Christakou et al, 2011, Marshmallow task (1 now vs 2 later):
- Tests temporal foresight, sensitivity to delay of reward, motivational inhibition, reflective vs impulsive decision making
- Younger participants predominantly chose now
- Kids who opted to wait for the two were shown to have a greater capacity for EF later in life
- Suggests development of these mechanisms starts young
Same study gave some evidence to what Neurodevelopment processes might be behind these effects:
- Progressive functional maturation of the vmPFC-striatal circuitry with age and performance
- Increased functional connectivity as well
- All of this associated with more reflective choice behaviour
Outline how functional connectivity develops in the brain?
- Increased connectivity between task-relevant regions with age while doing cognitive control, language, reward-anticipation tasks
- See a shift from local to distributed overall connectivity
- Specific regions become more/less connected e.g. front-striatal increases
- Anticorrelation between DWM and cognitive control networks
What is the Default Mode Network?
- DMN = a large scale brain network of interacting brain regions known to have activity highly correlated with each other and distinct from other networks in the brain.
- Essentially the brain’s “Neutral” mode
- Network that activates when not involved in focused attention
- Activates when patient is awake but not focused on a task, e.g. when day dreaming, but also appears to activate when thinking of others, thinking about yourself, remembering the past or planning the future
- Disruption of DMN related to a number of conditions e.g. Autism, Alzheimer’s
