Cognitive and brain development in children

Cognitive and Brain Development Before Birth

The brain of a human foetus develops rapidly and sequentially across gestation. Although cognition in the conventional sense (e.g. abstract reasoning or memory) does not emerge until after birth, foundational neurological structures and sensory processing abilities begin forming during specific intrauterine time windows. These processes can be divided into structural, functional and sensory milestones.

1. Structural Brain Development by Trimester

First trimester (0–12 weeks)

Neural development begins within days of conception. The neural tube forms by the end of week four, which gives rise to the brain and spinal cord.

Week 5: Forebrain, midbrain and hindbrain regions are visible.
Week 6–8: Neuronal proliferation begins. Primitive reflex arcs form.
Week 9–12: The cerebral cortex begins to differentiate, although it remains smooth and unconnected.

Second trimester (13–27 weeks)

Massive growth and organisation of the neural system occur. By 20 weeks, the brain has most of its future neurons.

Neuronal migration becomes dominant. Neurons travel to their final cortical positions.
Sulci and gyri begin to form on the cortex.
Glial cell production increases.
The thalamocortical connections (relay centre for sensory input) form between weeks 22–26.

Third trimester (28–40 weeks)

This stage is dominated by synapse formation, myelination and functional connectivity.

Cortical folding increases, improving surface area.
White matter tracts begin forming as axons are myelinated.
Synaptogenesis becomes dense in sensory regions.
The cerebral cortex begins regulating behavioural states like sleep and arousal.
Functional responses to sound, light and touch are detectable.

2. Functional and Sensory Milestones

Sensory System	Approximate Onset	Description of Functional Development
Touch	~8 weeks	Facial receptors develop first. By 20 weeks, the body is broadly sensitive. Reflexes like withdrawal appear.
Vestibular (balance)	~10 weeks	Inner ear structures form. The foetus can respond to changes in position.
Taste and smell	~12–14 weeks	Taste buds form by 12 weeks. By 20 weeks, the foetus can detect sweet or bitter amniotic fluid.
Hearing	~18–20 weeks	The foetus begins to respond to external sounds. By 25 weeks, the auditory cortex shows consistent activation.
Vision	~24–26 weeks	Eyelids open. Light penetration into the womb triggers retinal activity. Visual cortical responses are weak but present.

3. EEG and Brainwave Activity

18–22 weeks: Basic EEG activity begins. It is diffuse and low in amplitude.
24–28 weeks: Sleep-like brain states become distinguishable. Bursts of synchronous activity (spontaneous activity transients) occur.
32–36 weeks: More organised EEG patterns emerge, suggesting early cortical integration.
After 36 weeks: Sleep cycles with REM and non-REM phases develop. Responsiveness to familiar sounds like the maternal voice becomes consistent.

4. Foundations of Later Cognition

Although complex cognition does not occur before birth, several precursors form:

a. Neural circuits for sensory input are functional by the third trimester.

b. Thalamocortical connections enable the foetus to process external stimuli.

c. Foetal learning is demonstrable—e.g. changes in heart rate in response to repeated sounds suggest habituation by 32 weeks.

d. Recognition memory is suggested by differential responses to familiar versus novel stimuli.

5. Influences on Prenatal Brain Development

Several factors can enhance or disrupt foetal brain development:

a. Nutrition: Adequate maternal intake of folate, DHA and iron is critical for myelination and synaptogenesis.

b. Hypoxia: Reduced oxygen delivery (e.g. from placental insufficiency) impairs cortical development and increases risk of periventricular leukomalacia.

c. Infections: TORCH infections (e.g. cytomegalovirus, rubella) can cause structural abnormalities.

d. Drugs and toxins: Alcohol, nicotine, heavy metals and recreational drugs disrupt neuronal migration and synapse formation.

e. Maternal stress: Elevated cortisol crosses the placenta and alters hippocampal development.

6. Sequence of Brain Region Development

Brain Region	Function	Time of Functional Maturation
Brainstem	Reflexes, vital functions	7–10 weeks onwards
Thalamus	Sensory relay	Connects to cortex by ~24 weeks
Limbic system	Emotional reactivity and memory	Structures form by 20–24 weeks
Neocortex	Higher-order processing	Structural development from 8 weeks but functional integration occurs late (32+ weeks)

7. Summary of Developmental Milestones

Neural tube closes by week 4.
Major brain divisions and early synapses appear by week 8.
Thalamocortical connectivity forms by 24–26 weeks.
Functional sensory systems are mostly active by 28 weeks.
Sleep-wake states, EEG rhythms and learning responses emerge by 32–36 weeks.
Cortical maturity and connectivity peak close to term (38–40 weeks).

The unborn brain does not perform conscious reasoning, but it does acquire the sensory and neurological infrastructure necessary for postnatal cognition. Cortical function, sleep cycles, sensory reactivity and primitive learning are all observable before birth. These capacities establish the scaffolding on which complex cognitive development builds after delivery.

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Childhood Cognitive Development: Key Stages and Theoretical Models

Cognitive development refers to the progression of mental abilities such as perception, memory, reasoning, language and social understanding. The development of these abilities occurs in a structured and observable manner during childhood, influenced by both biological maturation and environmental input. Two dominant frameworks—those of Jean Piaget and Lev Vygotsky—offer contrasting but complementary accounts of how children's thinking evolves.

Piaget’s Theory of Cognitive Development

Jean Piaget proposed a stage-based model of universal development. According to this model, all children pass through fixed stages in the same order, although the exact age of transition may vary. Each stage reflects qualitatively different ways of thinking.

Stages of Piagetian Development

Sensorimotor stage (0–2 years)

Children experience the world through physical interaction. They develop object permanence and basic cause-effect understanding. Thought is rooted in immediate perception and action.
Preoperational stage (2–7 years)

Children begin using symbols and language. They engage in imaginative play and display animism and egocentrism. They cannot yet perform logical operations or understand conservation of quantity.
Concrete operational stage (7–11 years)

Children become capable of logical reasoning about tangible objects. They understand conservation, categorisation and reversibility. Egocentrism reduces and perspective-taking emerges.
Formal operational stage (11+ years)

Adolescents develop abstract reasoning and hypothetical thinking. They can manipulate variables mentally, form general principles and use deductive logic. Empathy becomes more sophisticated and moral reasoning matures.

Vygotsky’s Sociocultural Theory

Lev Vygotsky rejected universal stage models. Instead, he argued that cognitive development is shaped by cultural context and social interaction. He proposed that learning precedes development and is mediated by tools such as language.

Key Concepts in Vygotsky’s Theory

a. Zone of Proximal Development (ZPD)

This refers to the gap between what a child can do independently and what they can do with guidance. Learning is most effective within this zone.

b. Scaffolding

Adults and peers provide temporary support to help children perform tasks just beyond their current abilities. This support is gradually removed as competence increases.

c. Private speech

Children talk to themselves to guide their own behaviour. This eventually becomes internal thought. Language drives thought development rather than merely reflecting it.

d. Cultural tools

Cognitive skills are transmitted through cultural artefacts, symbols and practices. Learning is embedded within the norms and tools of the surrounding culture.

Comparison Between Piaget and Vygotsky

Feature	Piaget	Vygotsky
Developmental path	Fixed stages with biological triggers	Continuous change driven by interaction
Learning mechanism	Independent discovery	Guided participation and instruction
Role of language	Emerges after symbolic thought	Primary tool for developing thought
Abstract reasoning	Arises around 11 years	Emerges earlier if scaffolded effectively
Empathy and social insight	Progresses through logic and decentration	Built through social discourse and modelling
Role of adults	Minimal in early learning	Central to driving development

Emergence of Specific Cognitive Abilities

a. Hypothetical reasoning arises during the formal operational stage in Piaget’s model. In Vygotsky’s view, it may appear earlier if taught explicitly.

b. Abstract reasoning is linked to adolescent development in Piaget’s view but may develop earlier with exposure to conceptual language in Vygotsky’s model.

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