Neural Plasticity
The way the brain changes in response to stimulation from the environment.
Developmental Plasticity
The ability of synapses to be modified.
Developmental plasticity occurs before birth and through the early period of life and involves the development of
the nervous system.
Development of the nervous system goes through five stages:
1.
2.
3.
4.
5.
Proliferation
Migration
Circuit formation
Circuit pruning
Myelination
Proliferation: unborn baby’s cells that will be neurons divide and multiply. Up to 250,000 cells per minute.
Migration: newly formed neurons move to their destined location. The role of a neuron is determined by where it is
located when it is formed.
Circuit forming: axons of new neurons grow out to target cells and form synapses with them.
Circuit pruning: elimination of excess neurons and synapses. Pruning occurs during infancy and childhood, but there
is a second wave of pruning in early adolescence. Neurons that don’t ‘fire’ together get pruned.
Myelination: axons in the child’s brain become covered in myelin. This coating insulates the axon and prevents
electrical interference from other neurons. It also speeds up the rate of transmission of signals within the neuron
and prevents the neural impulse from leaving the axon before it reaches the axon terminals.
Myelination starts at the lower structures of the brain, before progressing to the cerebral hemispheres from the
occipital lobe to the temporal and parietal lobe and then finally the frontal lobe. The left frontal lobe is the last area
of the brain to undergo this process.
Adaptive Plasticity
The cerebral cortex retains plasticity throughout life. These parts of the brain can be shaped by learning and
experience.
Features of adaptive plasticity include:
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New connections between neurons (synapses) are formed or connections are altered (as a consequence of
change to environmental conditions when learning something new or when re-learning something after
brain injury)
Bushing/sprouting of dendrites and axons
Other areas compensating for areas of damage
Occurs throughout life
Rerouting/reorganisation of neural pathways
Timing of Experiences
Sensitive Periods
A sensitive period is a specific period of time in development when an organism is more responsive to certain
environmental stimuli or experiences.
Sensitive periods have set ‘start’ and ‘end’ times.
There are two types of learning during sensitive periods: experience-expectant and experience-dependent.
Experience-expectant learning: learning which occurs at any time during an individual’s life as a result of experience.
An example of experience-expectant learning is a young child’s learning of spoken (not written) language in the
native tongue of its family. This type of learning mostly occurs during childhood and adolescence.
Experience-dependent learning: occurs during sensitive periods and refers to experiences necessary for learning to
occur.
An example of experience-dependent learning is learning to read and write in one’s native tongue.
If an experience is missed out during a sensitive period, it does not mean that learning will never occur, but it will
take more time and cognitive energy for learning to take place. The learning might also, not be as efficient or strong.
Critical Periods
Critical periods are very narrow periods in time in an animal’s development in which the animal is pre-programmed
for learning to occur.
Imprinting is an example of a critical period. Konrad Lorenz studied birds and found that the first few moments after
birth are critical to imprinting (when the baby sees it’s mother and forms an attachment).
Critical periods are more common in animals. In humans we refer to them as sensitive periods, as they are more
flexible and cover broader time periods.