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How plastic is the adult brain?

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HOW PLASTIC IS THE ADULT BRAIN? For centuries, neuroscientist believed that neurogenesis within the adult brain remained fixed. Another assumption was that the higher vertebrates and humans are born with their full complement of neurons, with the restriction of postnatal neurogenesis taking place. The aim of this essay will target the new findings that will review the dogma that neurogenesis does occur and will be able to give a broader understanding of the complexity of the adult brain and its function. Previous research into neurogenesis assumed there was no logic that the adult circuitry had the capability of being able to add new components after development. Nevertheless, recent research has provided the key evidence that the adult brain does have the capability for neurogenesis to occur, which will bring this long held dogma down. Since the late twentieth century, new research into this dogma has proved to be wrong. It has now been established that there are findings in the brain that suggest that the stem cell do divide, however this occurs in two parts of the brain, the dentate gyrus (Gage et al., 1995) [2] and the subreventicula zone of the adult brain (Reynolds and Weiss, 1992; Richards et al., 1992). [2]They showed that we no longer^ had to consider that a complex neuron was required to divide for^ adult neurogenesis to occur. Now we know that these neurons can^ be generated from primitive cells, similar to what happens in^ development. Firstly, the dentate gyrus of the hippocampus, which is the part of the brain associated with our learning and memory. The second part of the brain is the subreventicular zone of the anterior lateral ventricles and its projection through the rostral migratory stream to the olfactory bulb that allows the new neuron to generate within the brain. The discovery of neural stem cells (NSC) and adult neurogenesis provides a new theoretical framework for understanding processes regulating brain plasticity (Gage 2000)[3] which are clearly present but they are suppressed from dividing. ...read more.


Eighteen patients had participated in the study either in which each subject had a case of a limb amputated or that they had brachial vision. Result showed that sensation could be felt in the phantom limb from the face on eight of the patient's. Also one amputee felt that his phantom arm extended straight out from the shoulder, as a result of this her always turned sideways whenever he passes through doorways. (Melzack 1992 [1]) Ramachandran went on to produce the `'remapping hypotheses'' Ramachandran p. which states that because there was a direct change in topography following differentiation. The remapping hypothesis also predicts that after trigeminal nerve section, one should observe a map of the face on one hand and shown in the remarkable study by Clarke et al 1996.The study conducted on a patient whose mandibular and maxillary parts of right trigeminal ganglion removed experienced referred sensations after stimulation of the right hand and right forehead. She described them either as parallel to the perception at the actual stimulation site or as coming uniquely from a (non-existent) stimulation of denervated territory. Thumb stimulations localized on the right side of the face, stimulations of right forehead, middle and ring fingers more precisely on right cheek. Referred sensations were present on postoperative day 7 and had a more real-like quality than 5 days later. After amputation of the index finger in one of the patient, a map of the index finger found neatly draped across the ispuateral cheek. (Aglioti et al 1994) Barsook et al 1994 found that even a few hours after amputation the pre-existing connection other than the sprouting receives support that there is sensation from the face to the phantom limb. Using his ingenuity and previous knowledge from the finding from his previous research, he invented a special tool to help his patients who suffer from mobility whether due to stroke or disease. ...read more.


A fundamental aspect of this stability was that no new neurons were added to the brain in adulthood (Gross, 2000).(8) In conclusion as to whether or not the adult brain is plastic still remains a controversial debate, however the findings to suggest that there is some activity of neurogenesis within the adult brain is outstanding. The dogma of neuroscience has always been that new neurons were not capable to reproduce in the adult mammalian brain. However, the acceptance of adult neurogenesis has shifted our view of the plasticity and stability of the adult brain. Due to the complexity of the brain and its complex function, it did not occur to researchers that the brain was in fact able to regenerate its damaged cells in certain conditions. This is a remarkable finding in the world of neuroscience because it means that we are able to get, yet better understanding of the human brain and its function. It has always been thought that the brain would stop producing until maturity and it would remain fixed in this critical stage. Because of this, it was thought that nerve cells could not regenerate, and that the functions controlled by the specific area of the brain would be lost forever. However, studies have shown remarkable evidence, which has proved this long held dogma down. Study by Ramachandran and colleagues result clearly showed that the brain was capable of reproducing new neurons, which is remarkable finding in terms of the complexity of the brain. This means that the brain has the ability to repair any damaged cells that may occur, which was always thought impossible because of the complexity of the central nervous system. However although we cannot say that the brain is fully plastic because there are some restriction for instance those whose suffer from disease such as Parkinson disease. Nevertheless, it should be taken into consideration that new research in the future could provide a better explanation required to help give a clearer understanding of adult neurogenesis and their potential to regenerate in the adult brain. ...read more.

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