To face disability in their after-stroke life (Smith and

 

To conclude, the human brain has the ability to develop
and change (functionally) throughout the lifespan, while adjusting to the
internal and external environment, also known as plasticity. In infancy and
childhood, the brain’s structural plasticity is supreme while in adulthood the
brain’s functional plasticity is dominant that constantly allows the brain to
adopt to changes (Demarin et al. 2014). Brain tissue holds the ‘use it or lose
it’ principle. Hence, if the neural pathway is not used, gradually it loses its
strength and it gets potholed. The surrounding brain tissues then compensate
and take over the function of damaged tissues (Fernandez and Goldberg, 2013).
Due to the compensating function of the brain tissue, some patients with
amputed body parts continue to experience the presence of lost part. In worse
scenario they feel the pain known as phantom limb pain in non-existing
(amputated) body part, which can be mild to severe and can lasts from few
seconds to many days, months or even years (Kalat, 2016). Due to the proven
brain plasticity theories, strong hope has emerged for the recovery of brain
damaged patients, especially for stroke survivors, as 50% of stroke survivors
face disability in their after-stroke life (Smith and Stinear, 2017). Although
there are different positive aspects of brain plasticity in human health and wellbeing
of humans, it is thought that increased cellular plasticity may have functional
signi?cance in some specific disease condition. It has been a concern that
during plasticity if the cell goes through tumorigenic transformation, a cancer
initiating cell develops which also holds plasticity feature and the two main
characteristics of these new cancer stem cells are plasticity and chemo
resistance (Yin et al. 2015).

 

Stem cells are the endogenous single robust cell of the
human body which are capable of self-renewal and hold the ability to replace
any other type of injured or pruned cells whilst maintaining and fixing our
body as needed. Due to maturation, diseased condition, or severe tissue damage,
an organism might face stem cell deficiency (Paul, 2013). During plasticity, if
the cell endures tumorigenic transformation (as a result of genetic mutations),
a tumour cell emerges which is known as cell-of-origin or cancer initiating
cell. Cancer stem cells are comparatively small subset of cancer cells that are
resistant to cancer treatments such as; chemotherapy and radiotherapy. This newly
formed cell also holds the characteristics of plasticity which develops tumour.
For the satisfying result to abolish cancer and to prevent deterioration,
treatment should be targeted to both cancer stem cells as well as young
tumorigenic cells (Rycaj & Tang, 2015). After conducting laboratory based research in different
settings, Yin et al. (2015) explain that the two main characteristics of cancer
stem cells are self-renewal (plasticity) and resistance to chemo therapy, and the
recurrence of tumor cells and failure to eradicate the cancer cells even after
chemo radiation therapy is due to the activation of stem cell genes which
promote cancer stem cell plasticity. Yin et al. (2015) further explain, some
genes such as Nanog, Oct4 and Notch are expressed by both normal stem cells and
cancer stem cells. Hence, it is crucial to identify whether the subset of
cancer cell is a real cancer stem cell.

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Stroke is one of the leading cause of death and
disability in this century. Stroke occurs due to the interruption of blood
circulation to brain tissues, either due to a blockage in the blood vessels or
with the haemorrhage, both leads to oxygen and nutrition deprivation to the
affected brain cells leading to death in severe cases and disability in less
severe cases. Frontal and temporal area of the brain are vulnerable to stroke.
Speech and swallowing problems, muscle weakness and paralysis are commonly seen
disabilities in stroke. The severity of weakness depends on the level of
damage. Due to the anatomy of brain function, the side opposite to the damage
is affected. Similar to other brain injuries, after a stroke, cortical
reorganisation happens to compensate the damage or injured cell functions
(Costandi, 2016). According to Smith and Stinear (2017), 50% of stroke
survivors experience ongoing disability. After stroke, during the first three
months, the neuroplasticity in the brain remains at its peak due to the spontaneous
biological recovery, and most recovery occurs at this stage. There will not be
spontaneous recovery at the chronic stage but post stroke therapies such as
motor trainings promote use-dependent plasticity. Li (2017) also highlights the
fact that neural reorganisation happens soon after the stroke which provides
the base of motor function recovery after stroke. This recovery relies on
spontaneous compensation recovery and motor learning during rehabilitation. Li
(2017) adds the importance of the therapist’s knowledge to differentiate the
spasticity and motor recovery, as they hold different mechanisms, and by
preventing the role of spasticity in impaired motor control also prevents maladaptation
in the recovery process and enhances successful management.

 

Kalat (2016) explains that most people with an amputation
(hand, leg or any other body part), experience a sensation of the amputed body
part even though it does not exist. This experience is known as phantom limb.
This sensation may be occasional to constant. It can be mild tingling sensation
to intense and unbearable pain which can last from few seconds to hours, days
and weeks or even for a lifetime. The cause of phantom pain was unknown until
the 1990’s. Kalat (2016) further explains that when the central nervous system
loses its usual input (after amputation), cortical reorganisation happens.
Hence, axons form another body parts take over the function of lost body part
(or the deprived neighbouring part). The stimulation of other body part
activates the synapses associated with the amputated area which now produces sensation
and it feels like it came from the amputed part. Richardson and Kulkarni (2017)
says, 50–80% of amputee experience the sensation of phantom limb pain. Many
treatments have been used to treat phantom limb pain including multiple drugs
(gabapentin, carbemazepam, propranolol, morphine, fluoxetine etc.), surgery (neurectomy,
rhizotomy, sympathectomy etc.), and complementary therapies (reflexology,
spinal cord stimulation, deep brain stimulation including the recent powerful
one, mirror therapy combined with movement representation technique etc.). However,
there is no first-line treatment for this category of pain as yet.

 

When the communication between neurones is interrupted
due to a certain condition (such as – hormonal changes, an injury, disease
condition or congenital anomaly) it directly affects the physical and
psychological (or both) health of a person depending upon the severity of the
disruption. Doidge (2016) claims that the human brain holds its own unique
power of healing as the brain cells constantly communicate with each other, and
form and reform new connections every moment. A longitudinal study done by
Dall’Acqua et al. (2017) also provides the evidence that connectivity changes
over time. When the brain faces functional hypo-connectivity due to a certain
reason, as compensation, the structural connectivity increases. In their human
based research, a mild traumatic brain injury, a partial recovery of the
injured brain was noted, however, they couldn’t conclude whether the full
recovery of the damaged functional and structural connectivity (up to premorbid
level) is possible.

 

In a normal brain, neuroplasticity betides under two
different conditions, external or internal. External change is due to the
changes in the external environment such as, input from the sensory system
(visual, auditory, olfactory, autonomic and somatosensory) on the developing
nervous system. While internal is attributable to changes in the internal
environment after a focal injury, hormonal reason or a disease condition. Due
to lost or altered input, secondary reaction happens to the remaining normal
tissue to compensate for the injury and to adjust in the new environment. This
aids in neural plasticity and is known as “lesion-induced plasticity” (Huttenlocher, 2002). Hormone plays an important
role in neuroplasticity. According to Kim and Strathearn (2016), hormonal
changes during pregnancy and postpartum period in a maternal body influences
the functional and structural plasticity of the mother’s brain. Oxytocin helps a
mother to maintain a special bonding and attachment with her baby. Oxytocin
level in a maternal body can fluctuate due to several reasons (such as;
troubled childhood, emotional or physical abuse, or trauma) which may affect
the maternal role. Chronic
stress can also cause atrophy to the prefrontal cortex and hippocampus which
causes negative impact on brain, and also can modify the structure of the
central nervous system. Impaired brain plasticity due to ischaemic disruption
is believed to be one of the main factor of cognitive impairment and more
disabling condition such as mood disorders, depression, vascular dementia and
atypical Parkinsonism (Cantone et al., 2017). Phillips (2017) has
explicated that a modifiable lifestyle is the key factor to maintain brain
health during ageing. A balanced diet and adequate levels of physical activity
influence common neuroplasticity substrates in the brain whereas cognitive
engagement enhances brain and cognitive reserve.

 

. Whereas, the volumetric changes in separate brain
regions due to different condition such as; change in white and grey matter
density, neuronal death due to injury or programmed cell death etc. is known as
structural plasticity (Demarin et al. 2014).

As stated by Davey et al. (2008), the brain plasticity
and self-organisation starts from the womb in response to the experience and
learning. Davey et al. (2014) further explains that the brain also prunes
itself as required throughout the developmental phase of human life. There are
two main types of neuroplasticity, namely functional plasticity and structural plasticity.
The permanent physiological changes in synaptic relationship between neurones
due to intracellular biochemical changes or structural adjustments, which
occurs during learning and memory is known as functional plasticity(Demarin et
al. 2014).

 

This essay provides an information on the structure and
function of the brain. It will then focus on brain plasticity and the evidences
that support the same. This essay will also include some information on phantom
limb, stroke recovery and stem cell plasticity.  As explained by Carter (2014), human brain
consists of neurons (which forms nuclei which in turn forms cortex), and is
well protected under the skull, with tightly packed meninges and blood vessels.
He further explains that the brain is divided into left and right hemispheres,
each with five lobes, which specialises in different tasks. Human brain enables
individuals to do the task they wish to by sending messages via its neural
pathways (Fernandez & Goldberg, 2013). According to Eriksson et al. (1998),
in the past, the human brain was considered as a soft static organ with no
signs of neurogenesis. However with the evidence based research in 1998, he claimed
that cell genesis occurs in the human brain. The human hippocampus holds the
ability to reproduce new neurons throughout the human lifespan reciprocating to
everything we do and to what we have experienced. This is known as
Neuroplasticity. As per Demarin et al. (2014), William James was the pioneer to
suggest the theory of neuroplasticity, who claimed that the human brain
acquires the capacity to change functionally, while Paul Bach-y-Rita was the
first to explain that the healthy part of the brain takes over the function of
injured or dead (neighbouring) brain tissue. As stated by Costandi (2016),
while explaining plasticity, Cajal in 1894 compared cerebral cortex as a garden
planted with numerous trees and clarified that the intelligent cultivation to
it produces flowers and fruits of greater variety and quality. Costandi (2016)
further adds that neuroplasticity is an essential and important property of
nervous system and it is present in all organisms that have a nervous system.
According to Doidge (2016), plasticity holds the principle ‘use it or lose it’
and it has been proved by many experiments. Doidge (2016) has also highlighted
the fact that if we receive pleasurable sensory input, which gives pleasant
sensation, plasticity can be perceived as a blessing. But this is not always
the case, in some cases the pain system can receive the sensory input, which
leads the presence of pain even after the original stimulus has stopped.