To What Extent Does Neuroplasticity

To what extent does neuroplasticity occur in congenitally blind people, and how can relevant advances in technology help?

INTRODUCTION

In this essay, I shall investigate the extent to which neuroplasticity occurs specifically in congenitally blind individuals. I will look at the effects neuroplasticity has on language and vision, and how new advances in technology may be able to help blind people through the premises of neuroplasticity. Research has suggested that the brains of congenitally blind individuals have different structures of those who were born with sight, due to neuroplasticity.

Neuroplasticity is a basic property of the nervous system and neurons. It produces adjustments to properties of the nervous systems affecting the structure of the brain. The phenomenon changes neural activity or behavioral responses by altering properties of neural elements. The changes can be caused during development, generated by natural or artificial changes in input, or due to neural damage. This essay will only concentrate on the changes in the brains of congenitally blind individuals. For someone to be considered to be congenitally blind, they must have been born with little to no sight. Their brains have different structures compared to those people who are born with sight, as the part responsible for vision is not used for that particular function, so another function will take place in that structure.

As there are many changes that can happen in the brain of someone who is congenitally blind, I will only be researching how language and vision can be affected through neuroplasticity. This is also based on the concept of sensory substitution, where one sense can substitute another, and that vision occurs in the brain through perception. The essay will also investigate the new technology that has been produced to help those who are visually impaired, based on the idea that neuroplasticity occurs in the brain. Normally, vision uses the optic nerve, which receives information through the eyes and then it is passed on to the occipital lobe where it processes information and the visual cortex, where perception takes place.

Research into the brain and neuroplasticity allows for the creation of new ways to help people. In this case, the advances in technology of neuroplasticity are used to be able to create different ways to help those who suffer from a vision impairment since birth. It also allows for the investigation of neuroplasticity and how certain impairments result with different brain structures being used for other functions. It could be argued that research into this area allows for a better understanding of the brain, which can lead to innovative ways of helping people who suffer from an impairment or a disease, by using as an advantage a naturally occurring phenomenon in the brain.

EVIDENCE FOR NEUROPLASTICITY

or a scientific theory to be accepted, it must be applied to certain criteria. A systematic approach through accumulated knowledge is needed to be able to understand how things work in the universe. A theory is accepted when it is based upon controlled and repeated experiments, there is consistent and sufficient evidence to support the claim, it is empirically testable, and is able to explain a certain phenomenon. In this case, neuroplasticity has been currently shown to be an accepted theory to explain the structural changes in the brain. This phenomenon is now widely accepted.

During many years there have been different theories concerning how the brain works and the occurrence of neuroplasticity. Ancient Greeks first thought that all organisms and bodily organs were perceived as anything but inanimate mechanisms, although this idea was replaced by Galileo Galilei (1564-1642). The polymath showed through his discoveries that planets could be understood as inanimate bodies moved by mechanical forces. He believed that nature worked as a large cosmic clock which is dependent on of the laws of physics. This lead to the explanation of bodily organs being compared and studied like they were machines. This concept was also supported by William Harvey (1578-1657), who studied under Galileo’s teachings. Harvey demonstrated that the heart works just as a pump and discovered how blood circulates through the body, supporting the idea that organic bodies work like machines. Furthermore, René Descartes (1596-1650), a French philosopher, also agreed that the nervous system and brain worked as a pump. This idea theorises that the brain is like a complex machine, consisting of a number of parts which perform a mental function. It was also thought that the brain is genetically hardwired, so no alterations can be made, therefore neuroplasticity could not take place. However, the French physiologist Marie-Jean-Pierre Flourens (1794 -1867) handled a series of experiments (1814-1822) with the removal of certain areas of the brain of pigeons, which aimed to investigate how it would affect its behaviour. Either the cerebellum or the medulla oblongata were removed. This resulted in the finding out more information about the functions of certain areas of the brain. For example, the removal of the cerebellum left the animal with no muscular coordination or equilibrium. It was found that the removal of large sections of the brain could also result in of any of the functions, without the result of a loss of any function, Flourens concluded that the brain works as a ‘functional entity’ which is able to organise itself. This is a piece of evidence for neuroplasticity, as it contradicted the previous beliefs of the brain is hardwired. However, it was still believed that the brain worked as a machine as there was still a large amount of evidence that supported the claim.

In 1868 the French neurologist Jules Cotard studied children who had a brain disease, in which the left hemisphere (Broca’s area- responsible for the ability to speak) was largely damaged. It was found that the children affected by the disease were able to speak normally. The findings suggested that if the Broca’s area is responsible for speech, the brain would have reorganised itself due to the brain damage, and the children were therefore able to speak. The findings showed that the brain was able to reorganise itself, as it was affected by a disease. Although this gives evidence of the occurrence of neuroplasticity, as the results could not be generalised to the rest of populations as it can be argued that those changes only happened due to the neural damage and because children’s brain has not fully developed, allowing for changes in the structure of the brain. The term neuroplasticity was first used by Ernesto Lugaro, an Italian psychiatrist, in 1906. It was believed that through a lifetime, the relations among neurons would change to adapt so psychic development, learning and brain damage recovery could occur. Many theories have suggested that neuroplasticity does occur, such as Donald Hebb, an American psychologist. The study suggested that during a learning process, neurons adapt – this is called the Hebbian theory. The theory suggests that if there’s a continuous connection between two neurons, chemical changes will alter the connection between both neurons, which leads to the process of learning. The theory proposes that the structure of neurons can be changed through behaviour. Moreover, a study by Ramón and Cajal (1984) showed the anatomy of a neuron for the first time, which later lead to the studies Tanzil and, Ramon and Cajal to separately propose that brain plasticity can occur at junctions between neurons (i.e. the synapse). Neuroplasticity was not accepted until the 1980’s by the scientific community. In past years, it was considered that it could not occur and that changes in the structure of the brain due to cortical damage were exceptions to what was believed.

The study Maguire et al. (2000) supported the occurrence of neuroplasticity. The investigation aimed to demonstrate the changes that occur in the organisation of the brain as a result of experiences. London taxi drivers were studied as it was hypothesised that their hippocampus, which is associated with memory, had a high dependence on navigation skills. Each participant was paired up with another right-handed, male non-taxi driver with to be able to compare brain structure with an MRI scanner with minimal differences between both participants. Therefore any changes in the brain structure were due to the participant being a taxi driver or not. It was found that the posterior hippocampus had significantly increased volume than the anterior hippocampus. Its volume correlated with the amount time of experience of the taxi drivers. The study shows how an input can change brain structure, and therefore it is evidence for neuroplasticity and supports the Hebbian theory. It is difficult to form a conclusion of this quasi-experiment, as a particular arrangement of the hippocampal grey matter could predispose individuals to a certain type of jobs, such as in taxi drivers who have a high dependence on navigation skills. However, there was a correlation analysis carried out which demonstrated that there was a positive correlation between length of time the participants had been taxi drivers and the volume of the posterior hippocampus. The findings could not be generalised to other people as the study only viewed the hippocampus of right-handed males, so the results could not be applied to females or left-handed individuals.

Studies concerning neuroplasticity have also investigated the changes in the brain of blind individuals. A study by Bach-y-Rita (1969) aimed to allow congenitally blind people to see through a device applying sensory substitution. It consisted of placing a metal plate which moved against the subject’s back, which scanned an image and conveyed it to four hundred vibrating stimulators. This procedure is based on the idea that sight does not happen in the eyes, rather in the brain, where perception takes place. The study allowed blind people to read, distinguish faces, shadows, and objects through the ‘tactile-vision device’. The study concluded that the brain is able to adapt information from a tactile receptor to allow a person to distinguish objects processed by a machine. Bach-y-Rita supports neuroplasticity, as the results suggest that the brain is able to adapt to information relayed from an artificial receptor via a tactile stimulus.

LANGUAGE

Language is defined as human communication, either spoken or written, consisting of the use of words in structured and conventional way. This process takes place in various regions of the brain which have shown linguistic capabilities. There are many structures and region in the brain that are accountable for the process of language, although other processes which do not have a direct connection to the understanding of language also contribute to this process. Vision and other variables can affect the meaning of spoken language, such as the behaviour and tone of someone might indicate what the meaning of what is said. In this section of my investigation, I will not be looking at the other variables and structures in the brain that might affect the understanding of language. Therefore, I shall be only looking at the structures that are responsible for language and any changes these might have through neuroplasticity in congenitally blind individuals.

The left hemisphere of the brain is considered to be responsible for speech and language, controlling the phonological, syntactic and lexical aspects of language, and only takes into account for communication. However, the connection between the left and the right hemispheres through the corpus callosum allows for the total understanding of language. It provides the ability to go outside of the limits of the literal meaning of words and engages different processes to do so. The right hemispheres allow the understanding of language that is used implicitly (i.e. metaphors), this is the pragmatic function. Individuals who have suffered damage in this region, have the pragmatic function affected and therefore can’t interpret implied additional meaning of language. The inferior parietal lobule, situated in the left hemisphere where there is a connection between the visual, somatosensory and auditory cortices. The neurons found in this region have been found to have multimodal abilities, so it can process different types of stimuli simultaneously. This function allows for the understanding of multiple properties of spoken and written words (i.e sound) and lets the brain be able to classify things, which enables abstract thinking and the forming of concepts. Brocas area has been suggested to be a very important region that is involved in language production and comprehension. It was first discovered by Paul Broca, who noticed that some patients that had specific speech impairments. The patients lost the ability capability to speak as a result of damage in a specific part of the brain. It is thought as a vital region in the understanding of language and speech. Wernickes area is also involved in speech and the comprehension of spoken and written language. These are the areas and structures that have been suggested that are involved in all the processes in the brain, although other variables (such as congenitally blindness) may change the function of some regions through neuroplasticity.

A study conducted by Massachusetts Institute of Technology (MIT) and Harvard Medical school showed that the occipital cortex, which normally functions for vision, is used by congenitally blind individuals in language processes. The study consisted of two experiments, where the occipital activity was compared in sighted and congenitally blind adults during sentence comprehension. In the first experiment, participants were asked to perform a sentence comprehension task and a difficult auditory task.