UCSF--Brain-Plasticity.jpg

Annabelle Jurd, z3254696; Pnina Kraus, z3292397; Jenny Tsui, z3283829; Celeste Chen, z3283463.




Media item






Introduction


The brain is constructed for change; it allows us to do things tomorrow that we could not do today. “Plasticity is defined as the brain's capacity to be shaped by experience, its capacity to learn and remember and ability to reorganise and recover after injury.” (Gleissner, Sassen, Schramm, Elger, & Helmstaedter 2005).

Brain plasticity occurs throughout life but is particularly evident at the beginning of life when the brain is forming its structures or at a time when brain injury occurs. The YouTube clip chosen is a documentary excerpt taken from Discovery channel. This excerpt exemplifies the phenomenon whereby the brain adapts and creates new connections between neurons to compensate for brain damage caused by a hemispherectomy. In this documentary, the resilience of the brain is demonstrated through a case study of a girl named Jodi. For the first three years of her life Jodi was a healthy child. However, soon after her third birthday epileptic seizures began to overcome the right hemisphere of her brain, resulting in loss of control of the left side of her body. When it was apparent that medication could not control the seizures, Jodi underwent a surgical procedure known as hemispherectomy, defined as the removal of a cerebral hemisphere. In Jodi's case, the entire right hemisphere of her brain was removed, and the cavity then filled with cerebral fluid. What was most extraordinary however, was not only that this surgery could be performed but within ten days little Jodi was up and walking with only slight paralysis on her left side. Her brain had begun creating new neural pathways almost immediately.

We chose this topic because Jodi's story is not only heart warming but is a testimony to the incredible adaptability of the brain. The brain is a fascinating and precious organ. It allows us to learn and grasp new concepts as well as interact with our environment. Our group was interested to investigate how, what and why this could all be possible. The media clip and the research allowed us to have a better understanding of the inner workings of our brain.

What follows is the neuroscientific context and analysis of brain plasticity in relation to Jodi’s case and particularly the ability of the brain to adapt and reconnect neurons at such a young age, when plasticity is at its greatest.




Neuroscientific Context


In most neuroscience literature, the term brain plasticity refers to the brain’s ability to learn, as well as recover from brain injury (Johnston, 2004). Over time, various definitions of brain plasticity have been derived, but Stiles (2000) suggests that there are 3 common features of plasticity that these definitions share:

1. Reference to process: plasticity refers to the dynamic process of the neural system, which brings change on a structural or functional level
2. Adaptation: plasticity results in the usage of new or different resources to deal with change
3. Organisation: plasticity is not haphazard and reflects a systematic interaction of structural features and environment.

The underlying mechanism of brain plasticity is simple: neurons communicate with each other through a cascade of electrical activity. These electric signals travel along the axon of the neuron to the dendrites of the post-synaptic neuron. Connections strengthen between neurons that constantly communicate with each other, forming neural networks. Communication between the neurons allow people to think, make decisions, perceive and interact with the world. When a person comes across an experience repeatedly, stronger connections are formed. Similarly, connections become weaker when one does not encounter an experience frequently. In principle, plastic changes in neuronal circuits are likely to reflect either modifications of existing circuits or the generation of new circuits (Kolb, Gibb & Robinson, 2003). This explains how people are able to learn abilities such as playing soccer or new information such as facts. Though the brain has a genetic blueprint of development, it is also shaped by the environment, and this can be interpreted as adaptive plasticity.

It has been argued that the brain's plasticity throughout a person's life undergoes two developmental stages (Merzenich, TED2004). The first epoch is a critical period, during which the brain is continuously 'plastic' and can be modified by any input. There are competitive plastic processes that help the brain to become a processing machine. For example; babies do not understand the meaning of words they hear for several months. The brain has to evolve in order to process the words. This occurs through natural competitive plasticity processes. In this period the child is constantly exposed to words, allowing the brain to set up a structure that will enable the child in later life to understand the meaning behind the words. It is important in the first epoch to make sure it is set up for such processes through exposure (Merzenich, TED2004). The brain is born without being able to control its plasticity. In the second epoch the brain takes control of plasticity. The brain learns to evaluate the consequences of actions and refines its abilities through selective attention. A person learns to focus on stimuli in the environment that are signficant to them, taking control of self- development. An example would be a soccer player who devotes attention to refining important skills for the game. As the person develops these skills the neural connections strengthen and change, due to brain plasticity.


Brain Plasticity After Brain Insult

Brain plasticity has been studied in many different clinical cases such as stroke, traumatic brain injury (TBI) and hemispherectomy. Hemispherectomy can be classified under two categories: anatomical and functional. Anatomical hemispherectomy refers to the disconnection and removal of the cerebral hemisphere from the cranial cavity, whereas in functional hemispherectomy the hemisphere is disconnected from the rest of the brain and body. Functional hemispherectomy was developed as a result of complications from the original anatomical procedure. (http://www.neurosurgery.pitt.edu/epilepsy/pediatric/surgery/hemispherectomy.html) For the purpose of our discussion, we will focus on the literature discussing brain plasticity after an anatomical hemispherectomy. Anatomical hemispherectomy, also known as cerebral hemispherectomy, was developed by Dandy in the 1930s to treat children with epilepsy and it continues to be a standard procedure in the USA after modifications to the original process. (Villablanca & Hovda, 2000)

Clinical cases have shown that recovery from brain damage in early childhood is more profound than in adulthood, as illustrated by their superior ability to learn a second language or their capacity to recover from brain injuries or radical surgery such as hemispherectomy for epilepsy (Villablanca & Hovda, 2000). Stiles (2000) believes the reason behind this increased capacity for plasticity is that the maturing brain system has not committed all its resources, hence these resources can be used to develop other functions in the case of a brain insult, showing great flexibility to minimise deficits. Mechanisms that explain great brain plasticity include persistent neurogenesis in certain parts of the brain. This overproduction can result in 2 year old toddlers having twice as many synapses in the cerebral cortex as adults, and these synapses are not pruned until adolescent period (16 years old).

Johnston (2004) suggested that there are 4 types of plasticity in children: a) adaptive plasticity which enhances skill development or recovery from brain injury; b) impaired plasticity associated with cognitive impairment; c) excessive plasticity leading to maladaptive brain circuits; and d) plasticity that becomes the brain's ‘Achilles’ Heel’ because it makes the brain vulnerable to injury. In Jodi's case, adaptive plasticity was illustrated. What happens is that changes occur in the neuronal circuitry that enhance a special skill with practice or allows the brain to adapt or compensate for injuries or changes in sensory input.

In addition to clinical cases, animal models have also contributed greatly to the development of the knowledge of what happens to the brain post-hemispherectomy, as neuroscientists are able to study systematically the neural and behavioural effects. Hence most literature on brain plasticity after a hemispherectomy are based on animal models. Margaret Kennard was one of the first to discover this difference after her work on motor cortex lesions in monkeys. She found that infant monkeys that were given lesions developed motor skills later, but adult monkeys lost all motor abilities. These experiments were influential and led to the creation of the ‘Kennard Principle’, which states that the earlier the brain damage, the better the restoration of function (Kolb and Wishaw, 1989).


Applications in Brain Plasticity

Motor effects
When people learn new motor skills, there are plastic changes in the structure of cells in the nervous system that underly motor skills. If the plastic changes are somehow prevented from occurring, the motor learning does not occur (Kolb, Gibb & Robinson 2003). Various investigators have shown that housing animals in complex versus simple environments produces widespread differences in the number of synapses in specific brain regions. Not surprisingly, post-injury experience as found by Kolb, Gibb and Robinson (2003) can modify brain plasticity and behaviour because such experiences as tactile stroking in cats are powerful modulators of brain development. It appears that regardless of inter-species discrepancies, the “Early Lesion Effect”, also known as the “Kennard Principle”, is still widely accepted. For example, Villablanca and Hovda (2000) found that adult-hemispherectomized cats showed great motor impairments such as weakness of the contralateral limbs and persistent turning to the side of removal during locomotion, while neonatal-hemispherectomized cats showed little or no deficits. In experiments with the lesioned brain, they found extensive remodelling of pathways in early lesioned cats, descending from the remaining sensorimotor cortex.

Visual effects
Although the maturation of the visual system starts before eye opening, a proper development of the visual system requires sensory experience. Adult animals reared in darkness from birth display serious physiological deficits in their visual cortex. Early experiments showing plasticity of the visual system were performed by Hubel and Weisel (1967), whereby they reduced input from one eye in kittens by lid sutre during their development so to affect the binocularity of the visual cortex. Such experiments proved the power of the plastic brain whereby the sutred eye lead to a large loss of cortical responses. However the opened eye appeared to make up for this by increasing the number of neurons, through plasticity preferentially driven by the open eye (Baroncelli, Braschi, Spolidoro, Begenisic, Sale & Maffei, 2010). Again, environmental experience appears to play an important role in brain plasticity and the brain's ability to recover from trauma, shown by Villablanca and Hovda (2000), whereby adult-hemispherectomized and neonatal-hemispherectomized cats show substantial contralateral hemi-field defect; in the adult group they have complete hemianopsia, but there was some vision for the neonatal group.

Language effects
The ability of the right hemisphere to sustain the acquisition or the recovery of language after extensive damage to the left hemisphere has been essentially related to age at the time of the injury. According to Pannier, Chiron, Jambaque, Renaux-Kieffer, Van de Moortele, Delalande, Fohlen, Brunelle and Bihan (2002) better language abilities are aquired when the insult occurs in early childhood compared with later occurence. The brain of a child has profound plasticity in that the right hemisphere has the ability to take over some expressive language functions, even at a relatively late age. In the case of Jodi her language was unaffected because it was her right hemisphere that was removed. However, it must also be noted that patients with lesions in the left hemisphere acquired in early childhood or prenatally show relatively normal language development as the right hemisphere takes over the language functions through brain plasticity.

Brain plasticity processes are reversible. When rats get to old age the brain looks dysfunctional but the plasticity can be reversed to make the brain functional again. We can use brain plasticity for correction, meaning that at any age, accuracy, strength and reliability of cortical representations, the co-ordination of cortical representations, the complexity of natural complex signal feature representations and the speed of cortical operation can all be improved (Merzenich, TED2004).


Analysis


In this documentary excerpt, the concept of brain plasticity was largely demonstrated though a case study of a girl named Jodi. The nature of this media item (a documentary excerpt from Discovery channel) suggests that its target audience is the general public - anyone who has access to Discovery channel, internet or an avid interest in brain plasticity and recovery of children.

Originating from Discovery Channel, an American satellite channel which largely airs educational videos on science and technology and accepted to be a largely reliable source, the information in this media item seems to be credible, pitched appropriately, and in an unbiased manner. Various experts in different fields appear in the documentary at different times to further explain the concept, which reinforces its credibility. Dr. Benjamin Carson, a pediatric neurosurgeon, illustrates brain plasticity in simple terms while Dr. Eileen Vining, a pediatric neurologist, takes viewers through Jodi's medical condition. The facts presented also seem to correspond with the current body of knowledge in neuroscience. In addition, the information was mainly presented in simple, layman terms, which was important considering that its target audience is the general public, most of whom have limited knowledge in this field.

It has been demonstrated that brain plasticity occurs in a wide range of contexts, and it has to be noted then that this documentary only seemed to focus on the case study of Jodi, and did not provide much information about the other aspects of brain plasticity. Brain plasticity is a broad concept and refers to more than just the recovery of a brain after the removal of a cerebral hemisphere. It can also refer to cortical re-mapping, or the ability to change the wiring of the brain after certain experiences. Phantom limbs, reorganization of the somatosensory cortex or visual cortex are all evidence of brain plasticity as well, something which the media clip does not provide details on. It is clear that a compromise was made between delivering the whole, complicated message and keeping the message simple. The result is a simplistic message, but only for a narrow aspect of brain plasticity.

Another limitation of the media item is tied to the presentation of information in terms of a case study. A case study is highly individualized, and results cannot be generalized to the general population. For instance, it cannot be assumed that another girl who undergoes the exact same hemispherectomy procedure would experience the same speedy recovery as Jodi.




Conclusion


In summary, brain plasticity is a dynamic and adaptive process that is best viewed as part of brain development, or a process that occurs after brain damage. The brain is a dynamic, responsive, and self-organizing system that is constantly rewiring according to experiences.

To maintain brain plasticity you have to exercise your brain continually, by continually learning and going through experiences. You need to nurture your brain. It is under your control and you can constantly change.





Search Strategy


Once the group had formed we sat down and started to brain storm different neuroscientific topics. Each group member came up with a suggestion of which topic seemed interesting to research. There were several topics that caught our attention, such as the effects of strokes on the brain, inception and brain plasticity. Once the suggestions had been put forward the group decided that brain plasticity was the most interesting and practical topic to research. We immediately started searching for media items on YouTube and came across the documentary on Jodi. The group felt that this media clip was appropriate for this assignment because it was informative and targeted at the general public.



References


Baroncelli, L., Braschi, C., Spolidoro, M., Begenisic, T., Sale, A., & Maffei, L. (2010). Nurturing brain plasticity: Impact of environmental enrichment. Cell Death and Differentiation, 17, 1092-1103.

Gleissner, U., Sassen, R., Schramm, J., Elger, C.E., & Helmstaedter, C. (2005). Greater functional recovery after temporal lobe epilepsy surgery in children. Brain, 128, 2822-2829.

Hertz-Pannier, L., Chiron, C., Jambaque, I., Renaux-Kieffer, V., Van de Moortele, P., Delalande, O., Fohlen, M., Brunelle, F., and Bihan, D. (2002). Late plasticity for language in a child's non-dominant hemisphere: A pre and post surgery fMRI study. Brain, 125, 361-372.

Hubel, D. H., & Wiesel, T. N. (1967). Cortical and callosal connections concerned with the vertical meridian of visual fields in the cat. Journal of Neurophysiology, 30, 1561–1573.

Johnston, M. V. (2004). Clinical disorders of brain plasticity. Brain & Development, 26, 73-80

Kolb, B., Gibb, R., & Robinson, T. (2003). Brain plasticity and behaviour. Current Directions in Psychological Science, 12, 1-5.

Kolb, B. & Whishaw I.Q. (1989). Plasticity in the neocortex: mechanisms underlying reovery from early brain damage. Progress in Neurobiology, 32, 235-276.

Merzenich, M. (2004). Rewiring the Brain, TED 2004 http://www.ted.com/talks/lang/eng/michael_merzenich_on_the_elastic_brain.html, filmed Febuary 2004.

Stiles, J. (2000). Neural Plasticity and cognitive development. Developmental Neuropsychology, 18, 237-272.

Villablanca, J. R. and Hovda, D. A. (2000). Developmental neuroplasticity in a model of cerebral hemispherectomy and stroke. Neuroscience, 95, 625-637