Applications of Plasticity :
Sensitive Periods for Learning
Developmental Plasticity
Adaptive Plasticity
Sensitive & Critical Periods for
Learning
•
Definition: refers to a very narrow period of time in
an animal’s development in which the animal is preprogrammed for learning to occur.
•
For example, ethnologist Konrad Lorenz studied how
young birds imprint (form an immediate attachment)
to the first moving object they see after they hatch
from the egg.
•
Lorenz found that greylag geese hatchlings imprinted
on him and followed him wherever he went.
•
For these geese, the critical period was the first few
moments of their life (Lorenz 1937).
•
In humans these critical periods are often referred to
as sensitive periods because the time in which they
occur is more flexible and broad than critical periods
for non-human animals.
Sensitive Periods
• Definition: Time an organism is more responsive
to certain stimulation
• Lack of stimulation can lead to long term deficit
• E.g. closed eye from birth leads to later blindness
even when eye eventually opened
• Language acquisition has a sensitive period (0 –
12 years)
• Learning a new language in teen years can lead to
the development of a second Broca’s area!
Review: Developmental Plasticity
• Changes as a result of experience and maturation
• Synaptogenesis – new neural connections
• Synaptic pruning – removal of synaptic
connections that are no longer needed
• Adults have less neural connections than a 3 year
old!
Review: Adaptive Plasticity
• The brain reorganises the way neurons in
different regions operate in response to a
deficit
• Deficits can occur from birth or as a result of
brain damage
Brain plasticity
http://www.youtube.com/watch?v=TSu9HGnlMV0
Neuroplasticity
http://www.youtube.com/watch?v=f0G8Lz5vFds&feature=related
Damage from Birth - Congenital
• Congenital – E.g. People who are blind from
birth may have occipital lobes that are used
for senses other than vision
• This may explain why people who are blind
from birth have very good hearing or tactile
sensitivity
Damage from Injury
• When a particular brain area is
damaged e.g. stroke other
brain areas can ‘take up the
slack’
• This is what happens when
people ‘recover’ from brain
damage
• Nerve cells do not regrow,
rather other neurons take over
the functions of the damaged
cell
• Rerouting – neurons near
damaged area seek new
active connections with
healthy neurons
• Sprouting – new dendrites
grow
• May occur near damaged area
of in other parts of brain
• Allows shifting of function
from damaged area to healthy
area
• ‘Relearning’ tasks like walking,
eating etc. helps these new
connections form
Adaptive Plasticity and Experience
Why is it so?
– Musicians have enhanced motor and sensory
areas
– Taxi drivers have enhanced functioning of their
parietal lobes
– Dancers motor areas are enhanced