Brain Development Notes

Explain the stages of brain development and describe how development changes throughout a lifespan.

At what age do you think a baby becomes a fully conscious human?
- Options:
  - 36 weeks at conception
  - 2 years old
  - 4 years old

Pre-natal: Conception to birth (3 trimesters).
- Peri-natal: Period just before and after birth.
- Neo-natal: Newborn baby (up to 36 hours old).
Childhood: Birth to approximately 12 years old.
- Progression: baby > toddler (mobility) > infant (language/autonomy).
Adolescence (Teens): Approximately 12 to 19 years old.
- Transition from child to adult.
- Cultural traditions often celebrate this as a 'rite of passage'.
- Physical maturity and a changed worldview.
Adulthood (Young/Middle/Old): Approximately 20 years old to death.
- Intimacies, relationships, and responsibilities (children, careers).
- Changes with old age: declining health, grand-parenting, end of life.

Brain development begins in the first few weeks after conception.
Most structural features of the brain appear during the embryonic period (first 8 weeks).
These structures continue to grow and develop during the foetal period (rest of the time in the womb up to birth).

Conception to two weeks:
- The neural plate forms and folds.
- By two weeks, it closes to form a neural tube.
By the seventh week (up to 3 months / 1st trimester):
- Neurons and synapses start to form in the tube.
- Early movement in the womb is enabled.

During the second trimester (up to six months):
- Myelination begins (fatty coating on the neuron’s axon to improve the efficiency of the electric current).
  - Starts in the brainstem and works along to the cerebellum
- Gyri and sulci (cortical folds) begin to appear.
- Basic sensory reaction (e.g., sound).
During 6 to 9 months (3rd trimester):
- Preparation for independence.
- The cerebral cortex begins to assume many duties previously carried out by the brainstem.
  - Foetal breathing, basic learning, and increased response to external stimuli.

Nature vs Nurture: Which is more influential?
- Genes, inheritance, and biology (nature) OR interaction with the environment (nurture), including the womb?
While the brain is developing in the womb, it is mainly biological (nature): based on what you have inherited from your parents ( $50/50$ ).
However, because no two twins are identical for any behaviours (at best usually $50-70%$ concordance / similarity), then other factors must come into play.
The environment (nurture) must modify genetic factors (nature) to create the end product.
- This is known as the ‘interactionist’ approach (nature & nurture interact).

A) Brain development from birth through to the end of childhood (12 years old).
B) Brain development adolescence (teens) – from around the age of 12 until 19 years old.
C) Brain development adulthood (young/middle/old) – 20 years of age onwards.

From birth, the brain rapidly develops, driven by environmental input (approximately 1000 neuronal connections a second develop during the first 6 months).
Caregivers need to provide a nurturing and stimulating environment to drive this initial development; otherwise, there can be consequences in the future.
Rapid development of:
- Voluntary movement
- Reasoning
- Perception
- Frontal lobes are active in development of emotions, attachments, planning, working memory, and perception (all based on memories [schemas] of past experience).
At birth, hearing and smell are quite advanced from experience in the womb (uterine).
Vision:
- Develops very quickly.
- Moves from a focal length of about half an arm (perfect to see mother) and from double vision (eyes working independently) to stereo 3D vision by the age of about 4 months.
By the age of three, the pre-frontal cortex is at its peak (reasoning, planning, etc.).
By age six, the brain is at 95% of its adult weight and peak of energy consumption (measure of how busy).

Neural connections, or ‘grey’ matter, are still pruning ('use or lose!').
Final wiring of brain is still a ‘work in progress’.
Fatty tissues surrounding neurons, or ‘white’ matter, increase and assist with speeding up electrical impulses and stabilize connections.
The prefrontal cortex is the last to mature; it involves the control of impulses and decision-making.
Teenagers tend to be reckless, irrational, and irritable.
- Often getting involved with alcohol, smoking, unprotected sex, and substance abuse.
The prefrontal cortex (executive brain) is not fully functional until about 22 years old (busy wiring for adult function).
Up to this age, an over-active ventral striatum (compared with adults) makes teenagers actively seek rewards.
An under active amygdala (emotions) makes a teenager less reactive to punishment and more likely to engage in risk-taking (not aware of consequence of behaviour).
The frontal cortex has a growth ‘spurt’ at about 12 years old and is then relatively dormant until about 22 years old, while it reprograms ready for adult thought.

20 to 65 years onwards:
- The brain reaches its peak power around the age of 20-22 years old and lasts for about 5 more years (e.g., prefrontal fully active).
- Afterwards, functionality diminishes.
- The brain functionality of executive control occurring in the prefrontal and temporal cortices are the last to mature and the first to decline.
- Memory for recalling episodes starts to decline, processing speed slows, and working memory stores less information.
- Best approach: stay mentally active, learn new skills, stay physically active, and eat a healthy diet. Avoid cigarettes, alcohol, and mind-altering drugs.
Older than 65 years:
- Brain cells are lost in critical areas such as the hippocampus (responsible for processing memories).
- Learning new skills, practicing meditation to promote neutral emotions, and exercise to improve abstract reasoning and concentration can slow neural degeneration.
- Maintaining cognitive use helps to slow down some diseases usually associated with old age (e.g., Alzheimer's [memory] and Parkinson’s [movement]).

A bell curve is a representation of normal distribution.
- When graphed out, it typically follows a bell-shaped curve.
From conception, our brain is continuously growing; we reach our peak growth around the age of 26.
- After the peak period, brain growth slows down and may decline.