Lecture 3

• Importance of prenatal development

  ▪ Fastest growth of body and brain ▪ Basis for further development ▪ Determined by biological factors, influenced by environmental factors
• 1st trimester phases

  1. Germinal phase (week 0-2) 2. Embryonic phase (week 3-8) 3. Fetal phase (week 9-38)
• Fase 1: Germinale fase (week 0 - 2)


  ▪ Primary objective:

  ▪ Development of zygote (cell created during fertilization) into blastocyte (layered cell mass with a cavity)

  ▪ Nesting in uterine wall

  ▪ Very sensitive phase: not always successful: up to 50% of

  pregnancies are short-lived, ending in miscarriage (often before

  pregnancy is detected)

  ▪ End of germinal phase: 250 cells
• Phase 2: Embryonic phase (weeks 3 – 8)


  Primary goal: • Formation of organs (including heart): organogenesis
• Phase 2: Embryonic phase (weeks 3 – 8), Three principles of growth:


  Cephalocaudal principle (from top to bottom): head → bottom, Proximodistal principle (from in- to outside): center → extremities, Orthogenetic principle (from mass to specific/undifferentiated to differentiated): simple → refinements
• Cephalocaudal principle (from top to bottom): head → bottom

  Newborn head accounts for 25% of its total lengths and 13% of total body weight versus adult head accounts for 12% of adult’s total lengths and 2% adult’s total weight
• Proximodistal principle (from in- to outside): center → extremities


  During first year of life the trunk/body is rapidly filling out, but arms remain short and stubby
• Orthogenetic principle (from mass to specific/undifferentiated to differentiated): simple → refinements


  A single cell becomes billions of highly specialized cells (e.g., neurons, blood cells, licer cells etc.)
• Week 3 – 4

  ▪ The inside of the blastocyst develops into three layers: ▪ The endoderm (becomes the digestive and respiratory systems) ▪ The mesoderm (becomes the muscle, skeletal systems and heart/circulation) ▪ The ectoderm (becomes the skin and nervous system) ▪ Neural tube (basic nervous system) ▪ Upper part of cylinder becomes brain, lower part spinal cord
• Week 5 – 8

  ▪ Formation of organs according to growth principles

  ▪ E.g. week 5: arms develop, then palms, of which fingers develop

  ▪ By the end of week 8, most structures and organs are developed
• Phase 3: Fetal phase (weeks 9 - 38)


  Primary objective:

  • Growth of the embryo and refinement of

  structures

  • Critical period for brain development

  Brain development

  • Increase in size

  • Doubles in size from month 4 to 7

  • From neural tube to ...

  • 100 billion neurons!

  • Formation of brain folding like adult
• Hearing fetus:

  ▪ Inner ear structures form by week 16

  ▪ Around 22-24 weeks cochlea, eardrum, ossicles and other crucial ear

  structures are fully formed

  ▪ What do babies hear: mom’s heartbeat, eating, breathing, walking, talking,

  exercising, burping, and digestive gurgling
• Seeing fetus:

  • Few external visual stimuli... • After birth: sharp sight at 19-21 cm
• Taste and smell fetus:

  • After 24 weeks primary taste ability • After birth: developed taste and smell
• Pain, fetus:

  • Pain ‘observed’ in premature babies of 24-26

  weeks

  • Neural system for pain perception ready

  around 26 weeks
• Touch, fetus:

  • From 8 weeks respond (moves) to touch
• Teratogens


  ▪ Harmful influences on unborn child (infectious diseases, medications,

  drugs, environmental toxins, nutritional deficiencies, maternal stress)

  ▪ Most harmful during embryonic phase (when organs formed)

  ▪ During 2nd and 3rd trimester negative impact on brain development

  ▪ Dose dependent: more = more impact

  ▪ But threshold: > 4 vs. 1 cup of coffee

  ▪ Individual differences in effects

  ▪ Depending on fetal and maternal (genetic)

  vulnerability (unpredictable)
• Teratogens: Smoking

  Consequence during pregnancy:

  ▪ Nicotine constricts blood vessels > reduces blood flow

  ▪ Less nutrients and oxygen for the child

  ▪ Effect strongest in last trimester

  Possible birth consequence:

  ▪ Increased risk of miscarriage

  ▪ Born too early/too small

  Later potential consequences:

  ▪ Asthma

  ▪ Cognitive problems

  ▪ Behavior regulation problems, ADHD, Antisocial

  behavior
• Teratogens: Alcohol

  Why problematic?

  ▪ Alcohol (ethanol) passes the placenta

  ▪ Alcohol cannot be broken down yet by the liver

  Consequence during pregnancy:

  ▪ Negative impact on neuronal development (proliferation, migration etc.)

  Later potential consequences:

  ▪ Fetal Alcohol Spectrum Disorder

  ▪ Fetal Alcohol Syndrome (FAS) → Specific cluster of congenital

  anomalies and developmental delays
• Key rules in brain functioning

  Hebb’s Law: Neurons that fire together wire together

  ▪ Repetition important for learning

  ▪ Neurons that are used repeatedly to perform a function

  become connected to facilitate performing the function

  Use it or lose it

  ▪ Synaptic pruning: old connections are deleted
• Major post-natal brain processes

  Synaptogenesis: Synapse formation

  Myelination: Insulation of neurons

  Synaptic pruning: Synapse elimination

  Apoptosis: Programmed cell death
• Myelination


  = Lipid-rich (fatty) substance speeds transmission
• ▪ Brain lateralization


  ▪ asymmetry and specialization of functions of the two brain hemispheres
• ▪ Gyrification (cortical folding)


  ▪ Allows larger cortical surface area → greater cognitive functioning
• Brain Development across the lifespan

  ▪ In childhood/adolescence: brain maturation

  ▪ In older age: brain atrophy (shrinkage)

  ▪ Coupé et al. (2017): comparison of brain volume trajectories in N =

  2944 aging from 9 months to 94 years old
• Grey matter:


  ▪ Mainly made of unmyelinated neurons and other cells →

  receives information and regulates outgoing information

  ▪ continuous lifelong decrease
• White matter:

  ▪ Mainly made up of myelinated neurons → transmits signals to

  other regions

  ▪ inverted u-shape, maturation peak in middle life
• Plasticity


  • Processes that allow the organism to modify itself as response to the demands

  of the environment → these processes could be due to:

  ▪ Development

  ▪ Learning and memory

  ▪ Cerebral changes (e.g., lesions, neurodegeneration, aging)

  • Greatest during early development
• Plasticity benefit


  some brain areas can take over the function of other injured brain

  areas (Example: blind baby’s develop better hearing ability)
• Plasticity challenge


  severe deprivation at very early age can have life-long consequences
• Plasticity: Older age & Physical activity

  ▪ Brain atrophy: PFC and hippocampus shrink in older age

  → however, less atrophy in adults that were more fit

  ▪ More fit (more physically active) older adults have greater brain volumes

  than less fit counterparts

  ▪ Greater gray matter volume in PFC

  ▪ Greater hippocampal volume and benefit on memory levels
• Sensation


  the product of the interaction between information and the

  sensory receptors – the eyes, ears, tongue, nostrils, and skin
• Perception


  the interpretation of sensory information
• Example sensation vs perception

  Visual sensation lets you detect the black and blue marks on

  this page; visual perception lets you organize the marks into

  letter and words
• Smell infants

  • Newborns prefer the smell of breast milk → soothing effect (e.g., less

  crying when mother is absent)

  • Newborns recognize the smell of their mother and her breast milk
• Taste infants

  • Newborns prefer sweet and are sensitive to other basic tastes

  • For bitter, sour and salty: stop sucking and involve face

  • For sweet: suck more avidly
• Smell older adults

  • Decrease in sense of smell is small, begins as early as adulthood

  • Ability to detect unpleasant odors does not change, for pleasant odors it gets worse
• Taste older adults

  • Decrease in sensitivity of taste; greater decrease in men → BUT: large

  differences between individuals

  • Reason decrease in taste: older adults produce less saliva → saliva

  transports chemical molecules
• Smell and Taste: Consequences for older adults

  • Negative impact on quality of life and physical well-being → associated with higher mortality

  • Less pleasure in losing in eating or eating spoiled food due to less taste and smell

  • BUT:

  • Taste and smell receivers are renewed throughout life and are influenced by environmental factors

  • Under optimal conditions, many older adults do not experience any negative consequences
• Touch infants


  • Skin-to-skin contact is important for bonding between baby and caregiver (increases chance of successful breastfeeding after birth)

  • Affects brain development (synaptogenesis, hormones) → Perhaps because babies become calmer and sleep better?