To conclude, the human brain has the ability to developand change (functionally) throughout the lifespan, while adjusting to theinternal and external environment, also known as plasticity. In infancy andchildhood, the brain’s structural plasticity is supreme while in adulthood thebrain’s functional plasticity is dominant that constantly allows the brain toadopt to changes (Demarin et al. 2014). Brain tissue holds the ‘use it or loseit’ principle. Hence, if the neural pathway is not used, gradually it loses itsstrength and it gets potholed. The surrounding brain tissues then compensateand take over the function of damaged tissues (Fernandez and Goldberg, 2013).
Due to the compensating function of the brain tissue, some patients withamputed body parts continue to experience the presence of lost part. In worsescenario 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 fewseconds to many days, months or even years (Kalat, 2016). Due to the provenbrain plasticity theories, strong hope has emerged for the recovery of braindamaged patients, especially for stroke survivors, as 50% of stroke survivorsface disability in their after-stroke life (Smith and Stinear, 2017). Althoughthere are different positive aspects of brain plasticity in human health and wellbeingof humans, it is thought that increased cellular plasticity may have functionalsigni?cance in some specific disease condition. It has been a concern thatduring plasticity if the cell goes through tumorigenic transformation, a cancerinitiating cell develops which also holds plasticity feature and the two maincharacteristics of these new cancer stem cells are plasticity and chemoresistance (Yin et al.
2015). Stem cells are the endogenous single robust cell of thehuman body which are capable of self-renewal and hold the ability to replaceany other type of injured or pruned cells whilst maintaining and fixing ourbody as needed. Due to maturation, diseased condition, or severe tissue damage,an organism might face stem cell deficiency (Paul, 2013). During plasticity, ifthe cell endures tumorigenic transformation (as a result of genetic mutations),a tumour cell emerges which is known as cell-of-origin or cancer initiatingcell. Cancer stem cells are comparatively small subset of cancer cells that areresistant to cancer treatments such as; chemotherapy and radiotherapy. This newlyformed 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 youngtumorigenic cells (Rycaj & Tang, 2015). After conducting laboratory based research in differentsettings, Yin et al.
(2015) explain that the two main characteristics of cancerstem cells are self-renewal (plasticity) and resistance to chemo therapy, and therecurrence of tumor cells and failure to eradicate the cancer cells even afterchemo radiation therapy is due to the activation of stem cell genes whichpromote cancer stem cell plasticity. Yin et al. (2015) further explain, somegenes such as Nanog, Oct4 and Notch are expressed by both normal stem cells andcancer stem cells. Hence, it is crucial to identify whether the subset ofcancer cell is a real cancer stem cell.
Stroke is one of the leading cause of death anddisability in this century. Stroke occurs due to the interruption of bloodcirculation to brain tissues, either due to a blockage in the blood vessels orwith the haemorrhage, both leads to oxygen and nutrition deprivation to theaffected brain cells leading to death in severe cases and disability in lesssevere cases. Frontal and temporal area of the brain are vulnerable to stroke.Speech and swallowing problems, muscle weakness and paralysis are commonly seendisabilities in stroke. The severity of weakness depends on the level ofdamage.
Due to the anatomy of brain function, the side opposite to the damageis affected. Similar to other brain injuries, after a stroke, corticalreorganisation happens to compensate the damage or injured cell functions(Costandi, 2016). According to Smith and Stinear (2017), 50% of strokesurvivors experience ongoing disability. After stroke, during the first threemonths, the neuroplasticity in the brain remains at its peak due to the spontaneousbiological recovery, and most recovery occurs at this stage. There will not bespontaneous recovery at the chronic stage but post stroke therapies such asmotor trainings promote use-dependent plasticity. Li (2017) also highlights thefact that neural reorganisation happens soon after the stroke which providesthe base of motor function recovery after stroke. This recovery relies onspontaneous compensation recovery and motor learning during rehabilitation.
Li(2017) adds the importance of the therapist’s knowledge to differentiate thespasticity and motor recovery, as they hold different mechanisms, and bypreventing the role of spasticity in impaired motor control also prevents maladaptationin 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 bodypart 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 sensationto intense and unbearable pain which can last from few seconds to hours, daysand weeks or even for a lifetime. The cause of phantom pain was unknown untilthe 1990’s. Kalat (2016) further explains that when the central nervous systemloses 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 partactivates the synapses associated with the amputated area which now produces sensationand 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. Manytreatments 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 powerfulone, 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 interrupteddue to a certain condition (such as – hormonal changes, an injury, diseasecondition or congenital anomaly) it directly affects the physical andpsychological (or both) health of a person depending upon the severity of thedisruption. Doidge (2016) claims that the human brain holds its own uniquepower of healing as the brain cells constantly communicate with each other, andform and reform new connections every moment. A longitudinal study done byDall’Acqua et al. (2017) also provides the evidence that connectivity changesover time. When the brain faces functional hypo-connectivity due to a certainreason, as compensation, the structural connectivity increases. In their humanbased research, a mild traumatic brain injury, a partial recovery of theinjured brain was noted, however, they couldn’t conclude whether the fullrecovery of the damaged functional and structural connectivity (up to premorbidlevel) is possible. In a normal brain, neuroplasticity betides under twodifferent conditions, external or internal.
External change is due to thechanges in the external environment such as, input from the sensory system(visual, auditory, olfactory, autonomic and somatosensory) on the developingnervous system. While internal is attributable to changes in the internalenvironment after a focal injury, hormonal reason or a disease condition. Dueto lost or altered input, secondary reaction happens to the remaining normaltissue to compensate for the injury and to adjust in the new environment. Thisaids in neural plasticity and is known as “lesion-induced plasticity” (Huttenlocher, 2002). Hormone plays an importantrole in neuroplasticity.
According to Kim and Strathearn (2016), hormonalchanges during pregnancy and postpartum period in a maternal body influencesthe functional and structural plasticity of the mother’s brain. Oxytocin helps amother to maintain a special bonding and attachment with her baby. Oxytocinlevel in a maternal body can fluctuate due to several reasons (such as;troubled childhood, emotional or physical abuse, or trauma) which may affectthe maternal role. Chronicstress can also cause atrophy to the prefrontal cortex and hippocampus whichcauses negative impact on brain, and also can modify the structure of thecentral nervous system. Impaired brain plasticity due to ischaemic disruptionis believed to be one of the main factor of cognitive impairment and moredisabling condition such as mood disorders, depression, vascular dementia andatypical Parkinsonism (Cantone et al., 2017). Phillips (2017) hasexplicated that a modifiable lifestyle is the key factor to maintain brainhealth during ageing. A balanced diet and adequate levels of physical activityinfluence common neuroplasticity substrates in the brain whereas cognitiveengagement enhances brain and cognitive reserve.
. Whereas, the volumetric changes in separate brainregions due to different condition such as; change in white and grey matterdensity, neuronal death due to injury or programmed cell death etc. is known asstructural plasticity (Demarin et al. 2014).As stated by Davey et al. (2008), the brain plasticityand self-organisation starts from the womb in response to the experience andlearning.
Davey et al. (2014) further explains that the brain also prunesitself as required throughout the developmental phase of human life. There aretwo main types of neuroplasticity, namely functional plasticity and structural plasticity.The permanent physiological changes in synaptic relationship between neuronesdue to intracellular biochemical changes or structural adjustments, whichoccurs during learning and memory is known as functional plasticity(Demarin etal. 2014). This essay provides an information on the structure andfunction of the brain. It will then focus on brain plasticity and the evidencesthat support the same. This essay will also include some information on phantomlimb, stroke recovery and stem cell plasticity.
As explained by Carter (2014), human brainconsists of neurons (which forms nuclei which in turn forms cortex), and iswell 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 enablesindividuals to do the task they wish to by sending messages via its neuralpathways (Fernandez & Goldberg, 2013). According to Eriksson et al. (1998),in the past, the human brain was considered as a soft static organ with nosigns of neurogenesis. However with the evidence based research in 1998, he claimedthat cell genesis occurs in the human brain. The human hippocampus holds theability to reproduce new neurons throughout the human lifespan reciprocating toeverything we do and to what we have experienced.
This is known asNeuroplasticity. As per Demarin et al. (2014), William James was the pioneer tosuggest the theory of neuroplasticity, who claimed that the human brainacquires the capacity to change functionally, while Paul Bach-y-Rita was thefirst to explain that the healthy part of the brain takes over the function ofinjured or dead (neighbouring) brain tissue. As stated by Costandi (2016),while explaining plasticity, Cajal in 1894 compared cerebral cortex as a gardenplanted with numerous trees and clarified that the intelligent cultivation toit produces flowers and fruits of greater variety and quality. Costandi (2016)further adds that neuroplasticity is an essential and important property ofnervous 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 highlightedthe fact that if we receive pleasurable sensory input, which gives pleasantsensation, plasticity can be perceived as a blessing. But this is not alwaysthe case, in some cases the pain system can receive the sensory input, whichleads the presence of pain even after the original stimulus has stopped.