functional recovery Flashcards
what is Functional recovery:
refers to the recovery of abilities and mental processes that have been compromised as a result of brain injury or disease.
What are some kinds of brain trauma that can result in loss of function?
Physical trauma - e.g. blows or missile wounds to the skull and brain
Viral or bacterial infections – these can destroy brain tissue (e.g. meningitis)
Stroke – interruption to the brain’s blood supply which may be the result of:
Cerebral haemorrhage – this is when a blood vessel in the brain bursts.
Those areas of the brain supplied by the blood vessel begin to die.
Cerebral ischaemia – this is when a blood vessel in the brain is blocked, e.g. by a blood clot (thrombosis) or by arteriosclerosis (thickening of blood vessel walls through fatty deposits).
Those brain areas supplied by the blood vessel begin to die.
Traumatic brain damage as a result of a stroke
can affect virtually all areas of behaviour and cognition.
It can lead to movement paralysis, language problems (aphasia), memory problems (amnesia) or difficulties with perception.
As the blood supply is lateralized within one hemisphere, strokes are often lateralized to one hemisphere, therefore the behavioural effects are likely to be one-sided.
For example, a left hemisphere stroke could result in paralysis on the right side of the body and may affect language (aphasia) as this is usually controlled by the left hemisphere.
In the 1960s, researchers studied cases where stroke victims managed to regain functioning.
These researchers discovered that when brain cells are damaged or destroyed, the brain re-wires itself over time so that some level of function can be regained.
It would appear that when areas of the brain are damaged, other parts appear able to take over the functions that were lost and neurons next to damaged brain areas can form new circuits that resume some of the lost function.
Mechanisms for recovery:
Reduction in swelling:
Neuroregeneration:
Formation of new connections
Stem Cells & Neuronal transplantation
Reduction in swelling:
A traumatic brain injury not only destroys neurons but can also cause the swelling of brain tissue.
This swelling can have an impact on behaviour. In the first few days or weeks following the brain injury, the swelling dies down and as a result there is often some significant improvement observed.
Whilst the reduction in swelling will lead to some improvement, regenerative developments in brain function following trauma arise from the brain’s plasticity, i.e. its ability to change structurally and functionally.
Neuroregeneration:
This refers to the regrowth or repair of nervous tissues, cells or cell products. Mechanisms for neuroregeneration may include generation of new neurons (neurogenesis), glia, axons, myelin, or synapses (synaptogenesis – birth of new synapses) to compensate for damage
Neurogenesis:
This is the growth of new neurons.
Until recently, it was thought that once the brain had matured, neurons could only be lost and not replaced.
However, we know that neurogenesis occurs at least in some areas of the human brain.
For example there is evidence of neurogenesis in the olfactory bulb and the hippocampus.
Formation of new connections:
Axonal Sprouting from surviving neurons: This is where the axons of surviving neurons grow new branches that make synapses in areas of the brain formerly supplied by the damaged neurons.
Neuronal unmasking: Within the brain there are “dormant synapses”. This is where
synaptic connections exist anatomically but their function is blocked.
Under normal circumstances these synapses may be ineffective because the rate of neural input is too low for them to be activated.
However, when the surrounding brain area becomes damaged, the rate of input to these synapses would be increased, which can then open (or “unmask”) these dormant synapses.
The unmasking of dormant synapses can open connections to regions of the brain that are not normally activated, creating a lateral spread of activation which, in time, gives way to the development of new structures.
Stem Cells & Neuronal transplantation:
the discovery of stem cells has led to a renewed interest in neuronal transplantation to enable functional recovery of the brain.
Stem cells are unspecialised cells that have the potential to grow into any cell type, including taking on the characteristics of nerve cells.
In theory, stem cells implanted in a damaged area have the potential to grow into neurons and make functional synaptic connections that would help restore behavioural functions.
There are a number of views on how stem cells might work to provide treatments for brain damage caused by injury or neurodegenerative disorders.
One view is that they directly replace dead or dying cells.
A second view is that transplanted stem cells secrete growth factors that somehow “rescue” the injured cells.
A third possibility is that transplanted cells form a neural network, which links an uninjured brain site with the damaged region of the brain.
Evidence for the role of stem cells in functional recovery
Tajiri et al (2013) provided evidence for the role of stem cells in recovery from brain injury:
They randomly assigned rats with traumatic brain injury to one of two groups.
One group received transplants of stem cells into the region of the brain affected by traumatic injury.
The control group received a solution infused into the brain containing no stem cells.
Three months after the brain injury, the brains of the stem cell rats showed clear development of neuron-like cells in the area of injury.
This was accompanied by a solid stream of stem cells migrating to the brain’s site of injury.
this was not the case with the control group.
Neuronal reorganisation:
transfer of functions to undamaged areas to allow functional recovery.
This can take place as a result of “axonal sprouting” from surviving neurons - axons of surviving neurons grow new branches that make synapses.
Rehabilitation and Neuronal reorganisation (including constraint –induced therapy):
We know from studying the intact brain that practising skills alters brain organisation.
For example, violin players who use their left hand for the complex fingering of the notes, the area of the motor cortex dedicated to the left hand increases with practice.
This has led to the suggestion that practice of a skill that has been affected by brain damage may lead to significant improvement.
One example that illustrates this is constraint –induced therapy (CIT).
Initially research into the effect of constraint-induced therapy was carried out on monkeys.
The monkeys were paralysed on one side due to brain damage. The therapy involved constraining the unaffected arm by placing it in a sling, the monkey then used their affected arm as much as possible.
The findings indicated that there was significant improvement in the affected arm. It was thought that the practice led to neuronal reorganisation in the motor cortex.
Further research has examined the use of CIT with humans.
This research demonstrated that CIT could be effective with language impairments (aphasia) following strokes.
Patients were given intensive practice in the area of language difficulty (e.g. speech) and their use of alternative communication (e.g. drawing and gestures) was restricted.
These patients showed significant improvement in the affected language skills compared to those patients who did not receive CIT.
It has been suggested it’s probable that the observed improvement was due to reorganisation of cortical networks in speech areas.
Factors that can influence recovery:
Age
Cognitive reserve
Age
It is a commonly accepted view that functional plasticity reduces with age (Huttenlocher, 2001).
However, studies have suggested that abilities commonly thought to be fixed in childhood can still be modified in adults with intense retraining.
Nevertheless, despite these claims of adult plasticity, Elbert et al (2001) concluded that the capacity for neuronal reorganisation is much greater in children than in adults, as demonstrated by the extended practice adults require in order to produce changes.
study that demonstrates the impact of age on brain plasticity:
Teuber studied soldiers with brain damage and found that recovery from movement and visual problems in adulthood was age dependent.
For example, 60% of those under the age of 20 showed significant improvement, whereas only 20% of those over the age of 26 showed a similar recovery.
It has therefore been suggested that axonal sprouting and reorganisation may be more extensive in the younger brain.
