III. Answer following questions
Define neural plasticity
It is the brain's ability to reorganize itself by forming new neural connections
throughout life. Neuroplasticity allows the neurons (nerve cells) in the brain to
compensate for injury and disease and to adjust their activities in response to new
situations or to changes in their environment.
Brain reorganization takes place by mechanisms such as "axonal sprouting" in which
undamaged axons grow new nerve endings to reconnect neurons whose links were
injured or severed.
The brain compensates for damage in effect by reorganizing and forming new
connections between intact neurons. In order to reconnect, the neurons need to be
stimulated through activity.
Neuroplasticity sometimes may also contribute to impairment.
Functional improvement after central nervous system (CNS) injury is a relearning
process. What does it mean?
After injury to the brain, there are two mechanisms whereby functional improvement
may occur. These are recovery and compensation (Kleim, 2007).
Recovery relates to:
1. Restoration of neural tissue initially perturbed after the injury (neural level)
2. Restoration of movement exactly as it was performed prior (behavioural
level)
3. Restoration of activity exactly as it was performed prior (activity level)
Compensation refers to:
1. Recruitment of new neural circuits (neural level)
2. Training of new movement sequences (behavioural level)
3. Training of activity in a new way after injury (activity level)
Recovery relates to lost functions being restored, and compensation relates to the
acquisition of new functions or behaviours to replace those lost after injury (Kleim,
2011).
What does experience- and learning- dependent neural plasticity mean?
experience dependent neural plasticity:
For neurons or networks of neurons to communicate they need to have extensive
connections with one another (or, quite literally hundreds to thousands of connections
for each neuron.) These extraordinarily complex connections require junctions or
connections termed synapses.
For example, neuron A connects via its axon terminal to neuron B at its dendrite. The
space between the axon and dendrite is the synapse. In a basic sense, the greater the
number of synapses, the greater and stronger the connections between neurons.
Likewise, the more synapses, dendrites and axons that develop, the greater the
opportunity to connect more neurons together and strengthen the existing connections.
As our experiences change, at a neurobiological level, we either increase or decrease the
numbers of synapses, dendrites and axons. If we stop a function, we lose synapses, etc.,
and if we increase an activity we proliferate synapses, etc., resulting in experiencedependent learning.
learning dependent neural plasticity:
When we learn new things the brain is able to carve new “roads” and to connect new
synapses to each other. If we keep travelling these new roads the brain begins to use
them more often and they get stronger and faster.
The learning dependent neural plasticity is not about accessing our “old” and already
well-travelled paths (for example our habits) it is about starting new ones. Of course
learning something new is more difficult than using the paths that already became
second nature.
What does "learned non-use" mean?
This occurs when, post-stroke, a paretic limb is not used due to the infarct affecting the
area of the primary motor area controlling that limb. Consequently, the individual relies
heavily on the unaffected limb and will not use the affected leg. With this behaviour the
primary motor area of the affected side will decrease his size and it will be even more
difficult to relearn movements after some time.
At the same time, the unaffected limb is substantially utilized, and the motor map for
that area increases in size. Learned non-use develops during the early stages following a
stroke as the patient begins to compensate for difficulty using the impaired limb by
increased reliance on the intact limb. This compensation has been shown to hinder
recovery of function in the impaired limb.
The CIMT (Constraint Induced Movement Therapy) is based on this theoretical
background. The quote “use it or lose it” plays an important role in this treatment.
The unaffected side is allowed to do just some little movements, the patient should try to
do as much as possible with the affected side to maintain the size of the affected primary
motor area in the brain and to maintain the axonal routes for the affected areas.