Theme 2A neurobiological development

Question 1

1. Motor cortex
2. Auditory cortex,
3. Somatosensory cortex
4. Visual cortex

Answer 1

1. Prefrontal: executive functions, attention
2. Temporal: language, hippocampus (memory)
3. Parietal: (touch), spatial functions
4. Occipital: object recognition

Question 2

Brain development: 2 periods

Answer 2

1. Growth (proliferation) and migration
2. Reorganization of the human cortex. Includes growth of dentrites and axons, synapse production and elimination (pruning), myelination
   → Related to functional/cognitive development

Question 3

Postnatal development 4 steps

Answer 3

At 2 years: 80% of adult brain size/weight
• But: developmental processes continue throughout childhood and adolescence:

1. Dentritic/axonal growth
2. Synapse production (synaptogenesis)
3. Pruning
4. Myelination

Question 4

1. Dendritic/axonal growth (postnatal)

Answer 4

• Axons and dendrites are formed after migration of neurons to the correct location

• Axons migrate to synaptic targets guided by chemical cues
> Often several cm
> Axons of motor neurons:
even up to 1 meter!

–> Initial overproduction of axons and dendrites

Question 5

2. Synaptogenesis (postnatal)

> Why is there an initial overproduction of synapses.

> Why is it important for functional development!

Answer 5

Initial overproduction of synapses.
Why?
• If damage occurs early in life: others may replace them • Provides the opportunity for a rich variety of experience
(e.g. sensory input) to affect development

Important for functional development!
• Period of overproduction important for onset (cognitive) function: synaptic density peaks coincide with onset function

Question 6

3. Pruning (postnatal)

Answer 6

Pruning = loss of synapses in absence of cell death
• Follows synaptogenesis
• Competitive and adaptive:
> Stabilization/strengthening of synapses that are most often used: depends on experience!
> Elimination of synapses that are not stabilized/ strengthened

–> Use it or lose it!!

Question 7

Use it or lose it: bilingualism

Answer 7

Language development monolinguals: ability disappears to perceive speech sounds/contrasts that do not exist in mother tongue
• Example: Contrast “L” en “R” in Chinese monolinguals
• Not used: these connections are pruned (eliminated)

Bilinguals: in Chinese children that are also exposed to a Western language, L/R contrast is conserved
• The connections are being used, and thus not lost!

Question 8

Synaptic peaks

Answer 8

• Synaptogenesis: MORE synaptic density in cortex (more gray matter)
• Pruning: LESS synaptic density in cortex (less gray matter)
• Peak in synaptic density coincides with onset cognitive
function
• Experience-dependent
• Regional differences

Question 9

1. Structural MRI
2. DTI
3. Functional MRI

Answer 9

1. Structural MRI: anatomical studies (gray/white matter density)
2. DTI: connectivity between structures
3. Functional MRI: activity patterns

Question 10

Development of structure & function

What did researchers find in DTI scans, the maturity of connections and reading ability?

Answer 10

Less mature: pruning adaptive to reading instruction

More mature: pruning less flexible to experience

So children with less white matter between Broca’s and Wernicke’s became better readers!

Question 11

Myelin

Answer 11

Fatty sheath insulating axons for more rapid impulse conduction
• Speeding up neural activity

Question 12

Give a summary developmental processes

Answer 12

• Axonal/dendritic growth, synaptogenesis: overproduction of axons, dendrites and synapses
> Gray matter increase

• Pruning: competitive synapse elimination. Experience- dependent, onset pruning related to onset function
> Gray matter decrease

• Myelination: formation of myelin sheath, increases conduction velocity
> White matter increase

• Different time-course of these developmental processes in different brain regions

Question 13

Experience-Expectant vs Experience-Dependent?

Answer 13

Child brain: experience-expectant

Adult-brain: experience-dependent

• Due to surplus of synapses in child brain
• Adult brain: half the connections of a 3-year-old
• Loss of synapses = loss of plasticity…?

Question 14

Critical Period

Answer 14

a limited time during which a child is biologically prepared to acquire certain capacities. Appropriate support is required within this window.

Lorenz’ imprinting studies
• Goslings form a picture (imprint) of the
object they should follow
• Imprinting during early & restricted
window
• Irreversible process.

–> Later research shows: periods of learning/plasticity do not end abruptly

Question 15

Sensitive Period

Answer 15

a time that is optimal for certain capacities to emerge because the individual is especially responsive to environmental influences. Development can occur later, but it is hard to induce.

Question 16

Which is more plausible: Critical or Sensitive periods?

Answer 16

Plasticity reduces, but some level is always retained

Question 17

Learning vs Plasticity

Answer 17

Plasticity:
“the adaptive capacities of the central nervous system – its ability to modify its own structural organization and functioning” (Bach-y-Rita, 1988)

Learning: flexibility of connections in neural networks enable learning

–> (lifelong) learning is possible because of (lifelong) plasticity

Question 18

Name examples of evidence in Cross-Modal neuronal plasticity research

Answer 18

Roder et al., 1999
Spoken sentences activate visual cortex in the blind

Sadato et al., 1996
Activation of occipital cortex during Braille reading in early-blind subjects

‘Seeing with the ears’ - TED talk

Question 19

Cross-Modal neuronak plasticity blindfolding

Answer 19

Only 5 days of blindfolding already leads to cross-modal plasticity:

visual cortex recruitment during tactile object processing