Critical Periods of Human Development

Raising Capable ChildrenSymposium on Early Childhood Development

Gilgit May 22-24, 2006

Camer Vellani AKU Human Development Programme

Introduction

• “Education is a great equaliser if all children have an equal opportunity to take advantage of it” -- Ramphela Ramphele, Managing Director, World Bank

• “As economic historians have pointed out, improved health, competence, and coping skills were a significant factor in the economic growth of Western countries after the industrial revolution” -- Fraser Mustard

“From Early child Development ot Human Development”Editor: Mary Young; World Bank, 2000

Adaptive property of the brain

Functions required for long term survival

Ability to learn

Responsible social behaviour

Maintenance of health

Functions of the brain influencing the ability to learn

• Memory

• Sensory perception – all modalities – stimulated by curiosity, motivation, interest

• Association

• Thought and concept formation

• Revision of concept

• Emotion

Concept

A concept is an abstract idea that is synthesised from several elements of knowledge

The synthesis has broader meaning and application than its elements considered separately

Functions of the brain influencing behaviour

• Memory of experience

• Concepts

• Self esteem

• Emotion

• Sex

• Application of thought

• Impulse

Functions of the brain influencing health

• Psychological determinants of behaviour

• Competence of the immune system

• Central control of voluntary and involuntary activities of all organ systems

Burden of mental and behavioural disorders

• Present at any one point in time in about 10% of the adult population

• Around 20% of all patients seen by primary health care professionals have one or more mental disorders

• One in four families is likely to have at least one member with a behavioural or mental disorder

The World Health Report 2001

Unique property of the human brain

Man’s ability to process, apply, innovate and express abstract thought distinguishes him from other primates and all other animals

Abstract thought is a complex versatile function of the cerebral cortex

Language

Words (symbols) and gestures are used to express thought

The sound and use of words is memorised accurately

The meanings of words and gestures are learnt by correspondence with action, through

processing of complex sensory perception

Organism Foetus Neonate Infant Child Puberty – Adolescence

Adult

Stages of

development

Formation and

Delivery

Physical growth and mental

development

Hormone mediated sexual differentiation and

mental development

Economic growth and reproduction

Spectrum of human development

D.

C.

B.

A.

OTICPLACODE

SOMITE 1

SOMITE 7

OPTICSULCUS

NEURALGROOVE

YOLK SAC

AMINON(CUT EDGE)

NEURALGROOVE

The dorsal aspect of a reconstruction of a 7-somitehuman embryo of about the 22nd day. The early optic sulcus is seen in the prosenephalic region. A — partially segmented paraxial mesoderm; B — roof of neural tube; C — pericardial area; D — branchial arch region. X c.47. Modified from Payne (1925).

A photograph of the left side of a 13.4 mm. C.R. length humanembroyo (estimated age, 40 days). The supra-umbilical swelling of the ventral body wall is produced by the liver and the pericardium. The heart can be seen within the latter. X c. 6.5.

HAND

EXTERNALAUDITORYMEATUS

OTICVESICLE

ROOF OF IVTH VENTRICLE

MIDBRAIN

OPTIC CUP

FOREBRAINVESICLE

UMBILICAL CORD

POSTERIOR VENOUS PLEXUS

MIDDLE VENOUS PLEXUS

ANTERIORVENOUS PLEXUS

CERVICALFLEXURE

Schemes to show successive stages in the differentiation of the cerebellar cortex. The superficial cortex and its derivatives are shown in red. The arrows in B indicate the probable migration of the cells. [Note synapses in the Dentate Nucleus in C]

Development of the cerebral cortex

• Begins when the embryo is 15 mm long• The germinal matrix lining the cortical lumen

releases 100 K neurones per day from weeks 8-24 then at a slower rate to a total of 100 billion at birth

• Neurones migrate under the influence of regional genetic control to their locations in the mantle of grey matter beneath the surface and aggregates deep within the substance of the cerebrum (parietal first)

Development of the cerebral cortex

• Neuronal migration results in layers of cells which connect later with the axons of cells located elsewhere but targeting cells in the cortex

• Differential cell death begins around 24 weeks with the reduction of cell release from the germinal matrix

Development of the cerebral cortex

• Once located each neurone synapses with 100 neurones

• Synapses progress rapidly until the age of 5 years, then more slowly to 18 years and continue through life

Development of the cerebral cortex

With increase in the size and weight of the brain at the end of the second trimester behaviour becomes complex

Sucking on hands and fingers, grasping, extending, flexing, rotating, sleeping and waking periodically and reacting to sound

Superimposed photographs of foetuses between the 3rd and 5th months of pregnancy. (Original)

Structural modulation of the cerebral cortex

• Utilisation of neural pathways modifies neuronal structures and connections over long distances

• Changes in activity of distant yet synaptically related structures alter inputs to the cortex and result in new physical and chemical relations between cells

Factors affecting growth and development in utero

Foetal nutrition and immunity which are dependent on maternal stores and nutrition, some requirements are small − Folic acid, iron, vitamin A

− Insufficiency results in failure of closure of the neural tube, anaemia and delayed development particularly of the brain

Factors affecting growth and development in utero

• Infections especially viral during organ formation e.g. Rubella− results in faulty development of the inner ear,

eye, brain and heart

• Environmental toxins absorbed by the mother e.g. lead, mercury, industrial waste and products of combustion

• Drugs and alcohol• Radiation

A measure of the rate of growth of the brain after birth is the rate of the growth of the head relative to the length of the body

Organism Foetus Neonate Infant Child Puberty – Adolescence

Adult

Stages of

development

Formation and

Delivery

Physical growth and mental

development

Hormone mediated sexual differentiation and

mental development

Economic growth and reproduction

Genes Maternal nutrition

and wellbeing

Health care

Management of disability

Parents, teachers, peers

Role models and peers

Public health system: health promotion disease prevention Social determinants of health

Education Mother, father, nutrition and

social environment Pre-primary and primary

Middle school

Secondary & high school

Technical or higher education

Work experience

Family beliefs and behaviours

Crucial determinants

of human development

Community: social, cultural, economic and environmental conditions

Conditions Influencing Human Development

Organism Foetus Neonate Infant Child Puberty – Adolescence

Adult

Stages of

development

Formation and

Delivery

Physical growth and mental

development

Hormone mediated sexual differentiation and

mental development

Economic growth and reproduction

Genes Maternal nutrition

and wellbeing

Health care

Management of disability

Parents, teachers, peers

Role models and peers

Public health system: health promotion disease prevention Social determinants of health

Education Mother, father, nutrition and

social environment Pre-primary and primary

Middle school

Secondary & high school

Technical or higher education

Work experience

Family beliefs and behaviours

Crucial determinants

of human development

Community: social, cultural, economic and environmental conditions

Critical outcomes

Activation of genetic

code

Survival

Learning ability, health (mental health and

immune competence) and behaviour

Health behaviour economic

growth

Conditions Influencing Human Development

‘Plasticity’ and critical periods of development

• Human development is shaped by interaction between biology and experience

• Structural platforms develop early through sensory perception that support learning, health and behaviour - the period for vision is critical

• Distinction between normal variations, maturational delays, transient disorders and persistent impairments is difficult

• Therefore, strive for conditions that support development for all and, for the disabled, conditions that support functional capability

Social environment in rural and urban Sindh (2002)

• Cross-sectional study of the growth and development of 1247 children aged less than 3 years and their social environment, funded by AKU at AKU

• Children with stunting (low height for age – indicator of chronic malnutrition) 39%

Bilal Iqbal, CHS: AKU National Health Sciences Research Symposium Sept 2003

Psychomotor Development Study of the social environment of children under 3 years in

urban and rural Sindh 2002 by Bilal Iqbal (AKU-CHS)

1527

41

8573

59

0

20

40

60

80

100

120

0 - 1 year 1.01 - 2 year 2.01 - 3 year

% D

istr

ibu

tio

n

Delayed Development Normal Development

Potential studies

• Effectiveness and limitations of formal education in relation to children’s learning ability

• Early nutritional determinants of proneness to chronic disease (diabetes, coronary disease, hypertension)

• Factors affecting – mental health and immune competence– resilience and gene expression for child development

and its sequelae– violence and tolerance of individuals and communities– economic growth, allocation of resources, and well-

being of individuals, families and communities