Neurobehavioural plasticity in development and ageing

Question 1

How does development occur?

Answer 1

More cells (neurones)
Bigger cells
More complex cells
More complex groupings - organisation into systems and structures will expand
Prerequisites or “building blocks”
- Biological substrate(s)
- Environmental context (external and internal)
- Capacity for plasticity of form and function
Putting the pieces together
- Stimuli and experience + brain systems = development

Question 2

What is plasticity?

Answer 2

The adaptability of an organism to changes in its environment or differences between its various habitats

Question 3

What can biological substrate(s) include?

Answer 3

Any aspect of the body
Its anatomy (form/structure)
Physiology (function/process)
Genetic material and mechanisms

Question 4

What do we focus on when we study the biological basis of behaviour/cognition?

Answer 4

Brain systems that provide the basis for all behaviour and cognition
Neurons, neurotransmitters, other cells and tissues
DNA/RNA, transcription, and regulation of neural processes

Question 5

What are the external aspects of environmental context?

Answer 5

Aspects that impinge on our senses or our minds in a psychological way or our bodies in a physical way

Question 6

What are the internal aspects of environmental context?

Answer 6

Aspects of physiology, such as the uterine environment on the foetus, or a person’s internal hormonal milieu (social environment) on brain and behaviour

Question 7

What is stimuli and experience?

Answer 7

Sound, light, tactile signals: all the waveforms, particles, objects and chemicals that contact the sensory receptors
- Spontaneous neural activity

Question 8

What is the central nervous system?

Answer 8

Spinal cord and brain

Function: integrates sensory information and responds accordingly

Question 9

What is the peripheral nervous system?

Answer 9

Nerves connecting CNS and body

Function: allows for complex movements and behaviours (heat or cold stimuli)

Question 10

What does the forebrain consist of?

Answer 10

Complex behavioural and cognitive functions
Cerebral hemispheres
Perception, coordinated action, integration of behaviour for purpose

Question 11

What does the brainstem consist of?

Answer 11

Hindbrain and midbrain
Basic functions and behaviours
Sensing, moving, survival reflexes

Question 12

What is glia/glial cells?

Answer 12

Constitute half of the brain volume

Physically and functionally support neural systems

Question 13

What are neurons/nerve cells?

Answer 13

Cell body: contains DNA and life supporting organelles
Axon: transmits input signals to the terminal fibres and is where the output signal is conveyed
Dendrites: receive neurotransmitter input signals
100-200 billion in adult brain
Many shapes and sizes depending on function
5-100 microns (1 micron = 1/1000 mm)

Question 14

What are the events as part of development?

Answer 14

Proliferation, Elimination, Organisation

Question 15

What is proliferation?

Answer 15

Characteristics that emerge and qualitatively increase in complexity and/or quantitatively increase in size or number

Question 16

What is elimination?

Answer 16

Characteristics that appear to decrease in size or number, or disappear altogether

Question 17

What is organisation?

Answer 17

Synergy of proliferative and eliminative events 
Consists of:
- Differentiation
- Migration
- Synaptic connection

Question 18

When does development begin and end?

Answer 18

Events are ongoing across the lifespan:

• Prenatal
• Postnatal (infancy)
• Childhood
• Adolescence
• Adulthood

Question 19

When change is more rapid at some points than others, what does it depend on?

Answer 19

The neurobiological system in question
Individual differences (genetics, environment)

Question 20

What occurs during the prenatal period?

Answer 20

Neural tube in the embryo (25 days) is the basis for all brain and spinal cord development
Neurons are cell bodies

Question 21

When is axon and dendrite proliferation the greatest?

Answer 21

From 7 months prenatal to 2 years postnatal (axons lengthen, dendrites arborise)

Question 22

What is the result of a genetically programmed development in conjunction with optimal environmental conditions?

Answer 22

Specialisation of cell anatomy and function

Question 23

What size is the brain at birth?

Answer 23

30% of the adult weight

Question 24

What is the state of the brain at birth?

Answer 24

Brain system development nearly complete, but higher order systems (e.g. cerebral cortex) take much longer to mature

Question 25

What occurs in the first 3 years of life?

Answer 25

A period of extensive proliferation - the maximum number of neurons and synapses is reached

Question 26

When is myelination (fatty layer accumulates around nerve cells) of axons most rapid?

Answer 26

4 months prenatal to 2 years postnatal

Question 27

What is extensive proliferation accompanied by during the postnatal period?

Answer 27

Extensive elimination as synapses form:

• some preliminary dendrites lost
• many neurons are lost (programmed cell death)
• synapses that don’t receive stimulation also die (synaptic pruning)

Question 28

What occurs in the childhood period?

Answer 28

Neuronal growth and synaptic connections continue, but at different rates in different brain systems

Question 29

When is 90% of the adult brain size reached by?

Answer 29

6 years

Question 30

When is the development of most aspects of brain anatomy and function completed?

Answer 30

Late adolescence

Question 31

What is limited in adulthood?

Answer 31

In vertebrates, the brain’s ability to repair and regenerate after damage is limited
…But, neuroscience frontiers are being “pushed back”

Question 32

What occurs in adulthood?

Answer 32

Synaptic connections continue to re-organise, largely in response to environmental conditions
Plasticity in a few areas is retained

Question 33

What is lost in the ageing process?

Answer 33

Neuronal number and size
Decreased volume of cortical grey matter (the cortex of the brain, which contains nerve cell bodies)
Reduction in efficiency of cellular functions
Cumulative damage
The frontal lobe is late to develop and also very sensitive to change in adulthood, including ageing effects

Question 34

When do the majority of neurons form?

Answer 34

Between 10-18 weeks

Question 35

When can changes in the adult brain anatomy and function be detected from?

Answer 35

20 years onwards

Acceleration of neural ageing can occur any time in adulthood - lots of variability across individuals

Question 36

What are the principles of environmental impact (continuum)?

Answer 36

Essential: nutrition, sensory input, social input
Negative: toxins, high stress, maternal malnutrition or illness
Positive: environmental enrichment, “optimal” stimulation

Question 37

What occurs during the sensitive periods (programmed plasticity)?

Answer 37

Timing differs depending on brain-behaviour system and environmental factor in question
Windows of maximum impact at a particular developmental point or phase

Question 38

What occurred in the experiments with rats that were either enriched or impoverished?

Answer 38

As adults, the EC group (compared to the IC) had greater arborisation of dendrites and more synapses per neuron

Question 39

What occurred with the handled rats compared to the rats that were not handled?

Answer 39

They were less fearful in novel environments (behaviour, physiology)
Have different brain organisation (anatomy, neurotransmitter function, behaviour)
Show less marked decline in cognitive performance with advancing age