What is infancy? (0-2)

• period between birth and the development of language (appx. 2 years)

Physical growth of the body - infancy

• marked by rapid growth rate

  • First 2 years rate of change is fast

  • slows down as we get older until it suddenly fluctuates during puberty

• We’re looking at rapid brain growth during infancy period

Puberty

• Point that sexual maturity is reached and capable of reproduction

  • Marked by enlargement of sexual organs

  • development of secondary sexual characteristics

• Genetic formula that is followed at middle teenage years

• Subject to environmental things

  • Found by secular trend in sexual maturation

    • Chart demonstrated

      • 150 years ago median age to hit puberty - 17

      • has declined overtime to ages 12-13

      • happens earlier in western cultures

• Reasons?

  • Industrialized places have eliminated genetic variances

  • chemicals in industrialized products, growth hormones, pollutants.

• Pattern in low SES children developing earlier than others in US (7-8 yrs)

  • Issues: cognitive abilities for reasoning (engage in drugs, sexual activity)

• Opposite things for males

  • Late puberty for males → less popular, attractive

• Stress, food, nutrition can cause puberty to happen earlier → War examples

Brain development

Ontogeny recapitulated phylogeny

• We as humans are related to other mammals → highlighted by the embryonic period

• development of individual is repeating the evolutionary changes that exists

→ Brain changes and becomes more “bumpy”, 27 weeks → 38 weeks

What happens during this period of change?

• period of the embryo

  • Neural tube becomes spinal cord

  • vertebrae armour around the tube to protect it

• At 13 days post implantation

  • inner layer creates membrane ‘straw”, → Neural tube

  • critical around 14 day period

    • If not developed can create birth defects or issues in development

  • All important for typical brain development to occur

• Failure of the neural tube to close causes (by day 30):

  • Top (develops into the brain) - condition called anecephalitis, failure of breathing

  • bottom (developes into the back, tail) - spinabifida

    • can vary in effects

    • Depending on where the closure doesnt happen, may be paralysis on bottom half of body

Stages of brain development

• Neuron production (completed by 18 weeks post implantation)

• Terminally differentiated → cell division that created that cell will not divide, reproduce again

  • Explains the problems of brain damage

  • Cant grow the neurons back

• Speed of neuron proliferation is fast

  • avg 100 billion neurons created during this period

  • all in place by 4 months

Neuron migration → movement of the neurons

• Moving to places they have to get, Can happen;

• Passively

  • Neurons dont move, but are pushed by other neurons

  • This type of migration is evolutionarily an old process

  • As new neurons are born, they push older neurons

• Actively

  • active in their movement, happens in cortical areas

  • born in the middle and somehow have to make their way to the top

Movement possibly happens with glial cells

• Help facilitate action potential

• Tidy up after neurons

Stages of brain development

Synaptogenisis

• creation of connections between neurons

• Happens around 5th week

Amount of synapse development between 0-15 months is remarkable as it keeps growing

• Babies have more synapses than us because there is more being created

Stages of brain development

Differentiation and specialization

synapse death and operating on Hebb’s rule

• environment plats most relevant role in the process

• Peak of synaptogenesis happens 8 months post natal

  • Noting the decline and levelling off on the chart

  • Why?

    • When you open your eyes, visual experience creates this spike

    • it then starts pruning excess branches created prior to 8 month period, that are not connected to important things

    • improving in visual acuity from elimination of excess branches