Brain Development MK

Question 1

What are some of the periods that the brain goes through in development

Answer 1

– sensitive periods (e.g. cochlear implant)
– critical periods (e.g. ocular dominance)
– staged behavioural maturation
– later shifts e.g. Rett syndrome – adult plasticity

Question 2

As a baby, the brain has specific properties which change as you mature.
What does your brain look like?

Answer 2

Physically smaller (4x)- but has more neurons, with more potential, less knowledge
Less myelin
Shorter dendrites
Axons are less branched

Question 3

What are the FOUR basic processes that nervous system development follows?

Answer 3

1. Generation and migration of neurons
2. Outgrowth and guidance of dendrites
3. Connection and feedback between neurons
4. Functional plasticity and maturation.

• They need to occur in that order- each phase depends on the prior

Question 4

Neurons are flexible

Answer 4

Form on the basis of chemotaxis, patterns of activity, trophic factors, and guidance cues interact, so even if one system is disrupted, connection patterns will make some kind of sense.

Question 5

Neurons accomodate change

Answer 5

This is our way of survival- adaptation
even substantial mutations which alter the brain will still recover
For example- the reeler mutation whereby the cortex forms inside out, but it is still, at least, workable

Question 6

What is Lissencephaly? Why does it Occur

Answer 6

Lissencephaly, or ‘smooth brain’ occurs due to the reelen mutation in humans- means that you will have epilepsy, other cortical dysfunction such as intellectual deficits.

• abnormal formation of the cortex

Question 7

What normally develops postnatally?

Answer 7

Dendrites!
• Most axon and dendrite growth in the cortex occurs after birth; timing depends on area
• Responsible for large increases in cortical volume early in development

Question 8

Organising the adult brain AND stripping down the cortex

Answer 8

Patterns and activity shape and strength synapse connection.
These factors ensure tha tfunctional connections are favoured during maturation.
Such rules also 
 permit reorganisation 
 in the adult brain

During subsequent development, we choose the best from among the new dendritic connections, thinning the cortex. Myelination also locks in the selected arrangements

Question 9

Optimisation

Answer 9

Implication of myelination + thinning of the cortex in sight of connectivity is that as the brain matures it will optimise itself for the current conditions
Major interventions are therefore most effective if they are delivered as soon as possible (once the system is ready for them of course).
This may apply to chronic medication of children if medication affects the CNS.

Question 10

What are the two key elements to structural refinement of the cortex?

Answer 10

1. SYNAPTIC PRUNING: we know that OPTIMISED DENDRITES need FEWER synapses. The frontal region of the brain finishes last (at around 25).
   At age 12-15 , 30,000 connections are eliminated every second.
2. MYELINATION: dynamic process of myelination and demyelination- increase into 40s, declines from 60s. in the cortex, primary sensory regions myelinate first, then association areas- prefrontal last.

Question 11

Functional maturation involves two periods- what are these, describe

Answer 11

• maturation processes are time linked
  1. sensitive period: a time during which a system is susceptible to MAJOR change (eg. cochlear implant age)
  2. critical period: a sensitive period during which changes are irreversible (eg. occular dominance oclumn)

Question 12

What is a critical period?

Answer 12

Sensory systems have specific times when they commit to their adult organisation

Deprivations, such as congenital cataracts, can permanently alter the structure of the brain – even if corrected later

The example used over and over is the cochlear implant- if not put in before 6 months IT will fail to establish CORTICAL RESPONSES -> ie. critical period has been missed

Question 13

What happens post critical period ?

Answer 13

PLASITICITY!
Other plasticity transitions occur later on
• e.g. in Rett syndrome, a dysfunctional allele of the X chromosome transcriptional regulator MeCP2 means nervous systems don’t sustain adult plasticity mechanisms

• With defective plasticity, they lose synapses, and become severely intellectually disabled- hippocampus and cortex atrophy; synapse loss • Behaviour, learning, body mass all affected • Shows MeCP2 dysfunction is critical at this age

Question 14

Behaviour develops with your brain

Answer 14

Developing behaviour shows consistent patterns related to the maturation of the brain structures involved

Question 15

What are the 3 stages of STAGED BEHAVIOUR?

Answer 15

1. OPPORTUNITY Vs. READINESS: children seek out the correct type of stimuli to promote the next stage in their development . If they dont get the right experience, they may miss out on crucial developmental input.
2. Interaction between SYSTEMS: eg. blindness can delay motor development
3. STAGE APPROPRIATE EXPERIENCE: just that prem babies that are overstimulated don’t do very well.

Question 16

Experience and Development

Answer 16

EXPERIENCE EXPECTANT: Hard WIRING versus EXPERIENCE DEPENDENT aspects of development.

eg. speech sounds- all mammals respond preferentially to speech sounds (experience expectent) but human infants go on tofavour the sound of their own language (experience dependent)

Question 17

Cognitive Stages

Answer 17

Growing children show abilities which reflex level of mental complexity.
abilities build on each other in a series of stages! eg. object permanence at 10months, crucial for later dvt of language.

Question 18

Example of cognitive staging- eating and food preferances

Answer 18

1-2: children accept new foods easily
2+ : become selective

Theories:
-Cashdan: survival instincts (need to judge whats safe to ingest)

Question 19

How does survival eating come into food preferances?

Answer 19

In wild environments, plant material is often toxic, and safe can be difficult to distinguish from unsafe
• Children are less biochemically able to handle toxic compounds
• Meats and ripe fruits, however, are rarely toxic
• Compare to infant behaviours:
– far more fussy about vegetables, despite their high nutritional value
– distrust new foods, requiring multiple presentations
– these preferences emerge at the same time as other behavioural independence from parents

Question 20

Food preferance transition

Answer 20

Sharp onset of food 
 preferences represents 

the maturation of a behavioural system
• Preferences established here set the boundaries of adult behaviour – which foods are acceptable and which are disgusting
• Cashdan likens this to a “critical period” of food preferences – setting lifelong parameters

Question 21

Why ADHD stimulants are bad

Answer 21

Used on children (stimulants like Ritalin and Adderall), they alter NA and DA processing in the brain - behavioural effects (and abuse)
• Brain therefore matures with alterations to its modulatory systems unknown outcomes

Question 22

MAIN POINTS

Answer 22

• Physical formation and hookup of the brain precedes functional maturation
• Structural changes to the brain during childhood and adolescence
• Sensitive and critical periods
• Behavioural changes correspond to nervous system maturation