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• During the embryonic period, the embryonic disc develops into a three-layered structure.
• The three layers of the embryonic disc:
  • Ectoderm (outer layer)
  • Mesoderm (middle layer)
  • Endoderm (inner layer)
• By day 15, a group of cells grows rapidly at one end of the ectoderm, creating a basis for the head and brain.
• Between weeks 3-4 a neural plate forms following chemical signals sent to the ectoderm.
• By day 20, the neural plate folds along its midline, forming a groove.
• By week 4 (around day 22), the folds arch over the groove to form the neural tube.
• The neural tube gives rise to the brain and spinal cord.
• Folding begins in the middle of the groove and proceeds towards each end until sealed, except at the ends.
• By 3.5 weeks, a swelling appears at the top of the neural tube, showing three divisions by week 4.
• These divisions correspond to the future forebrain, midbrain, and hindbrain.
• After the closure of the neural tube in week 4, neural development involves several overlapping phases

Neurogenesis

• Involves neuron production in the embryo.
• Neurons are made from other cells in the neural tube that divide rapidly.
• Neurogenesis begins around weeks 3-4 and continues up to week 16.
• Most brain neurons are formed by week 24.
• Rapid neuron proliferation causes the infant's head to enlarge to half of its body size by week 8.
• Neuron production generally decreases at birth, but it may continue in the adult brain, possibly in the hippocampus.

Neuronal Migration

• Neurons move to appropriate locations in the brain and body.
• Neurons migrate varying distances via a pushing or pulling process under genetic and biochemical control.
• This migration establishes different neural populations that contribute to brain structures and systems.

Neuronal Differentiation

• Genes modify newly arrived cells to specialize them for their roles in brain regions and systems.
• Synaptogenesis and myelination occur during embryonic cell differentiation.
• Synaptogenesis: The development of connections or synapses among neurons.
• Dendrites: Extensions/branches at the top of the neuron.
• Terminals: Extensions/branches at the bottom of the neuron.
• Myelination: Coating axons with a fatty insulating material to improve efficiency.

Final Phase

• Prenatal brains have a surplus of synapses.
• Neural development involves pruning connections and competition among neurons.
• Basic brain structures are present by weeks 9-10 of the foetal period, and growth in brain mass occurs thereafter.
• The cerebral cortex shows increasing folding due to neuron production, synapse growth, and myelination.
• Different brain regions develop at different rates.
• Embryos display basic behaviours and responses reflecting organized neural activity.

Prenatal States

• Foetuses show daily rhythms activity, and hormone release by the end of the first trimester.
• REM sleep cycles appear around 28 weeks gestational age and decline to about 50% by birth.
• Prenatal development and infancy are critical for the early development of the brain.
• They are especially critical for the organization of the visual, auditory, touch systems, and formation of memories.

Prenatal Abilities and Behaviours

• Sensing and responding to external stimuli is a fundamental capacity.
• The five main sensory systems begin development in the embryo.
• The five senses: vision, touch, hearing, taste, and smell

Touch

• Touch is the earliest sensory channel to develop.
• By 8-9 weeks, a foetus moves its head when touched in the mouth region.
• By 12 weeks, a foetus will grasp at anything touching the fingers.

Taste and Smell

• Taste develops at around 18 weeks, and smell at around 15 weeks
• The foetus familiarizes itself with the smell and taste of the amniotic fluid.
• The foetus shows preference for its own mother's amniotic fluid at birth.

Auditory/Hearing

• This functions to some extent by about 20 weeks.
• The foetus will respond to loud sounds with movements.
• By 22 weeks, the foetus shows a more sophisticated reaction by orienting or attending to sounds.
• If a sound is repeatedly presented, the foetus habituates, showing evidence of simple learning or memory.

Vision

• This is the least developed sensory channel in prenatal life.
• By the fourth month, the main parts of the eyes develop
• The next month sees cells specialise along the visual pathways for processing colour and spatial detail.
• By the 7th month, the visual cortex develops.

Postnatal Brain Development

• Many brain systems for sensation and perception are functioning well at birth, as is the ability to learn and remember.
• The neonatal brain is developed sufficiently to allow the infant to perceive, and is adaptable to context.
• The neonatal brain is 25% of its adult weight.

Postnatal Connecting and Pruning

• Newborn brains have one-sixth of the synapses found in adult brains.
• Synaptogenesis increases in the months after birth.
• There is a rapid increase in the number/length of dendrites/terminal branches.
• The infant brain has twice as many synapses as the adult brain by 12 months of age
• Synaptogenesis and pruning do not occur uniformly across brain areas
• The brain regions for sensory processing show these processes the earliest.

Lateralization

• Left Brain Development after birth: This hemisphere shows bias for positive emotion and categorical perception.
• Right Brain Development after birth: This hemisphere show dominance in processing relational patterns, colour categorization and emotional arousal.

Developmental Neuroscience

• This involves studying brain regions/systems.

Developmental Cognitive Neuroscience

• This involves studying the brain during different states and activities related to processing.
• FMRI study found long-range connections increasing from the frontal cortex to visual and sensorimotor areas.
• EEG patterns in the resting brain develop in the first 12 months, becoming adult-like.

EEG (electroencephalogram)

• Electrodes placed around the scalp record brain activity.
• Used to map infant brain activity during different states and cognitive tasks.
• Brain activity in the form of 'waves' from the scalp detected.
• Dense-array sensor-nets make it easier to apply.
• Recent EEG approach finds bursts of activity linked to different cognitive processing types.
• EEG frequencies are grouped in bands related to how frequently the waves occur.
• Theta waves appear in the brain when holding items in working memory.
• Beta activity appears in the brain when processing environmental information
• Alpha activity appears in the brain when awake but in relaxed mode. Superfast gamma arise when the synchronisation of all activity within the brain regions.
• Similar EEG activity types are found in the infant brain.