Psychology: Brain Development Through the Lifespan

• Psychology lecture notes on brain development from conception to old age.
• Professor Heather Cleland Woods (she/her) can be contacted via [email protected].
• Student hours are on Monday from 3 pm to 4 pm, in Room 440 at 62 Hillhead Street.
• The lecture will cover the structure and function of the nervous system.
• Key stages in brain development from conception to adulthood will be covered.
• Discussion on environmental influences on brain development is included.
• Changes that occur to the brain with aging are discussed.

Neural Induction

• Occurs from day 18-24.
• It's genetically determined.
• The neural tube forms and ends close during this stage.
• Neural patterning occurs, where cells acquire different identities and dimensions.

Proliferation

• Occurs from day 24-125.
• It's genetically determined.
• The brain produces 250,000 cells per minute.
• By day 125 (mid-pregnancy), the foetus has all its cells.
• A single layer of cells, called the "Ventricular Zone," forms along the inner surface of the neural tube.

Migration

• Cells move from the bottom level toward the top level to their final destinations.
• Radial glial cells act as scaffolding to help other cells migrate.

Differentiation

• Occurs from day 125 to postnatal.
• Cells differentiate into specific types like hippocampus or cerebellum cells.
• Cells express particular genes to make specific proteins, acquiring distinctive features.
• Transplanted immature cells adopt the characteristics of their new area.

Synaptogenesis

• Neurons develop more axons and dendrites, leading to the formation of synapses.

Cell Death/Stabilization

• There is an initial surge in synaptic growth.
• Synaptic growth levels off and declines after the first year.
• Cell death prunes the brain to bring about balance.

Synaptic Rearrangement

• Axons initially reach out widely, forming a diffuse pattern.
• Adjustments occur where active synapses are strengthened.
• Synapses that are not active become weaker.
• A more focused pattern of synaptic contact remains.

Brain Development at Birth

• Total brain volume doubles in the first year and reaches 80% of adult size by age 2.
• The basic structural and functional framework is in place by the second year of life.
• Development after age 2 mainly involves reorganizing and fine-tuning major circuits.

Brain Development in Childhood

• There is rapid postnatal growth of cortical grey matter over the first 2 years.
• Slower growth of cortical white matter occurs throughout childhood and adolescence.

Brain Development in Adolescence

• There is a higher ratio of white matter to grey matter.
• Synaptic connections at dendrites in the grey matter decrease.
• Synaptic connections are refined to make space for mature patterns to form
• Initial changes occur in the occipital/parietal lobes, followed by the frontal/temporal lobes.
• There is an increase in axon myelination in white matter, which speeds up information flow.
• Myelinated nerves can carry impulses up to 100 times faster.
• Functional connectivity between the prefrontal cortex (PFC) and subcortical structures does not reach a stable state until the mid-20s.
• The imbalance model of brain development suggests that reward-related subcortical regions and prefrontal control regions interact differently across development.
• Motivational and emotional subcortical connections develop earlier than those supporting prefrontal control.
• The result in adolescence is greater reliance on motivational subcortical regions rather than prefrontal regions.

Environmental Influences on Brain Development

• The focus is on prenatal and childhood periods.

Prenatal Tobacco Exposure

• Nicotine is the most prevalent substance used during pregnancy.
• Toxins in tobacco can cross the placental barrier.
• Tobacco can dampen the gene expression of foetal brain regulatory genes responsible for brain growth, myelination, and neuronal migration, altering brain structure and function.
• It results in long-lasting effects like a risk for psychiatric disorders and addiction.

Prenatal Maternal Stress

• A foetus can be exposed to increased maternal cortisol.
• Maternal can impact functional and structural brain connectivity involving the amygdala, PFC, and hypothalamic-pituitary-adrenal (HPA) axis.
• It can increase the risk for behavioural and mental health problems later in life.

Prenatal Maternal Depression

• Prenatal depression is associated with elevated maternal cortisol levels.
• Maternal cortisol levels can predict a larger amygdala in 7-year-old children.
• Amygdala volume partly mediates the association between maternal cortisol and child affective problems.
• Infants born to mothers with higher prenatal depressive symptoms show greater functional connectivity of the amygdala with key brain regions involved in the activation and regulation of emotional states, such as areas of the PFC.
• This observation aligns with connectivity patterns seen in adolescents and adults with major depressive disorder.

Socio-economic Status

• Higher childhood SES is associated with prolonged structural and functional brain development, leading to more efficient cortical networks in adulthood.
• For low SES, greater exposure to chronic stress accelerates brain maturation.
• It leads to faster maturation of stress-related circuitry (e.g., amygdala, medial frontal cortex).
• Stress can cause faster ageing of the entire body via increased glucocorticoid levels and allostatic load (physiological "wear and tear").
• Poverty affects mental/physical health and life outcomes through toxic stress.
• In 389 typically developing children/adolescents aged 4-22 years, living below the poverty line was associated with an 8-9% reduction in grey matter in the frontal and temporal cortex and hippocampus.
• Grey matter reductions explained 15-20% of the income-related achievement gap.
• Neglected children had a mean frontal-occipital circumference (reasonable measure of brain size) below the 5th percentile.
• Brain size improved when children were removed from neglectful environment and reassessed after 1 year in foster care, especially when younger.

Changes with Ageing

• Structures that mature earlier are more resistant to ageing effects, compared to those that mature later.
• Grey matter in the prefrontal cortex (PFC) declines by about 5% per decade from age 20 onwards.
• Age-related decreases in hippocampal volume are associated with declines in working memory, episodic memory, processing speed, and executive function.
• The HAROLD (Hemispheric Reduction in Older Adults) model describes increased bilateral recruitment of prefrontal areas to compensate for structural decline.
• For example, in working memory tasks.
• The PASA (Posterior Anterior Shift in Ageing) model describes recruitment of the prefrontal cortex in response to reduced visual cortex activation.