Why is brain plasticity necessary ?

Brain development is based on genetic information and from a mechanism of adaptation to the environment. However, during the gestation period, since the uterine environment is very similar in the majority of individuals, the brain seems to grow based on genetic information, so it will be developing bases of the mechanisms that will be run later, that allow interaction with the external world. The genes that determine this polarity, are called organizers genes and they are not only expressed in the nervous system, but in other tissues and organs. While the genes that direct the differentiation-specific structures known as regulatory genes because they govern not only the anatomical structure but the function of the cells (Poch, 2001).

The reasons why the distribution of structures and the development agenda are preset are not very clear, but one theory is that the nature or complexity of the functions and the genetic programming can perhaps obey physical laws that govern other natural processes. In this sense Walsh and Diller (1981) explain that the brain maturity is a progression of neural development, which is determined by two types of neurons that built the kind of connections that are established between structures. On the one hand, pyramidal neurons (called macro neurons) differ from the neurons of local type, by which the first develop much earlier, establishing early connections then it will be difficult to restore after a brain injury, apparently these neurons are genetically clip-art and are running during birth, and they are responsible for establishing the functions of lower order, for example in the case of language, sound analysis and its phonological representation; while local neurons, will enjoy a longer liberty or plasticity and will be responsible to establish new connections in more advanced developmental periods. This type of neurons will be involved in the processes of higher order, is consolidating in a more progressive way and involved in functions such as semantic processing (Tubino, 2004).

In this way, brain plasticity mechanisms may include neurochemical changes, on cortex, receivers or structures, so it’s possible to say that functional plasticity is accompanied by structural plasticity, most important among the mechanisms of functional reorganization are the unmasking, the synaptic bud, the dendritic arborization, inhibition and facilitation and modification of neurotransmitters, among others, so it admits the possibility that there are several types of neuronal plasticity, which are considered to a) the developing brain plasticity; b) plasticity of the brain in learning period and c) plasticity in the adult brain (Aguilar, 2003).

Plasticity of the brain in development

Deacon (2002) explains about the plasticity of the brain in development, that during the period of embryogenesis genes are those who will determine the distribution of the different brain tissues and will also be responsible for the coordination of the processes that later will take place in the formation of the embryo, including the basic structures of the brain; but after the birth the genetic will run other mechanisms of brain structure that will largely depend on the environment both internal and external.

 

So at the beginning of the development of the nervous system, there is an excess of neural fibers, and an important part of the development process includes the neuronal trimming of excessive connections that are not necessary and may in fact be can be harmful to normal operation. 

In fact, thought this explosion of connections as early is part of the process of plasticity during development, and this has advantages of adaptation. However if any damage occurs during the period in which there are excessive and available connections, there are more possibilities of the system to survive despite the damage that you can design a route of alternate connections that may be suitable for the repair of the damage (Avaria, 2005).

It is so accepted that there are moments or critical periods in which each of the different areas of the central nervous system has special sensitivity and responsiveness to the changes induced by the different influences, and there is enough evidence about the influence of the experience affects most the final organization of the local circuits which to the main roads, because time has already completed the topographic organization of large circuits. 

But even if there is a period of particular sensitivity to receive sensory information that ultimately is going to influence and direct the learning, so although there is a certain structural predisposition that is set from the beginning and favors a previously established connection ans its maintain, this connection depends on the strength of the neuronal signals, as no matter where come from those signals but are retained and are finally established. However, is known that the age in which the injury occurred is one of the crucial factors to take into account to predict the course of brain injuries, as it has been found in research that focal lesions before one year of age will have a worse prognosis of intellectual function that injuries of the same type after that age (Riva & Cazzaniga 1986; Woods, 1980;  Tubino, 2004).

In this sense, since plasticity is greater in the first years of life, for most of the lesions and gradually decreases with age, the learning and the recovery will be enhanced if experiences are provided or stimuli early to the individual, especially in children, since the structures nerve in the first years of life are a maturation process that continuously new synaptic connections are established and growing myelination occurs their structures, so that in response to the stimuli coming from the experience, and by means of internal biochemical processes, the infant brain is forming. 

During this critical period, the circuits of the cerebral cortex have, as already mentioned, large capacity of plasticity, for which the absence of an adequate intake of stimuli, experiences or nutrients has important future functional consequences (Wash and Diller, 1981; Deacon, 2000; Hernandez-Muela, Mules, Mattos, 2004; Avaria, 2005).

 

Even when you know some of the factors that control the duration and the time that establishes these periods of special sensitivity, described that they relate to particular synaptogenesis, i.e., the phase in which there is hiperproducción of synapses in the cerebral cortex, but, as already explained, of these synapses will lose those neurons that do not establish any relevant connection finally will be eliminated by the system, giving rise to a phenomenon of remodeling of the brain network, so it is said that genetically predetermined development configures phases of production or synaptic outbreak (Wash and Diller, 1981).

However, there is evidence that not all the brain areas show periods of synaptogenesis and synaptic loss at the same time. In the primary visual cortex, for example there is an outbreak of synaptogenesis by 3-4 months of age with a maximum density at 4 months. But in the pre front cortex takes longer and reaches the synaptic density maximum to 3-5 years. The time course of the Elimination of synapses is also more prolonged in the frontal cortex (up to 20 years) than in the visual cortex (4 years); so, it is possible to affirm that maturation times for different brain structures are different, and the primary areas senso-motor cortical unfold before large areas of association. 

In this sense, el made that are necessary stages so that neural activity to complete development, involves the brain maturation is changed through his own stimulation and experience, providing the necessary adaptability to the brain. This scheme is probably cheaper from the biological point of view, since a model whereby the genetic control for the formation of all synapses is needed would require a incredible number of specific molecular markers and their respective genes, what a system rigid and dependent would do it. This is explained because of the extreme immaturity of the brain of the newborn, whose fragility justifies the total parental dependence of the newborn human. This emphasizes the total difference of man with respect to most of the animals, which even newborns, they are already capable of running many of its basic functions (Tubino, 2004).  

Also known that the ability to analyse and synthesize multiple sources of information, and generate different responses from the brain, which illustrates the centralized organization and brain function, there is a hierarchy in the organization in such a way that the lower segments carry out specific functions subject to the control and modulation of segments above, by which the complexity of the information processing increases progressively as the level becomes to up to the crust. But, from the periphery may cause, with certain stimuli, responses in higher levels that force the organization or the acquisition of certain functions. 

However, it has been particularly studied the early lesions that occur in the linguistic areas, which generally manage a good recovery function, but currently, there is extensive evidence that the process of recovery of functions is not able to completely eliminate the effects of the early focal lesions as in the case of the language, throughout the subsequent development of the infant, you can see difficulties in reading, writing, comprehension, articulation, fluency and/or syntax (Verger and Junque, 2000)

One possible explanation of this effect, is that all the sensory and motor regions primary brain are related from a functional point of view, by association fibers. Cortical association areas, for example, are directly connected among themselves, while the primary cortical areas are connected each other indirectly through the Association areas. Homologous areas in both hemispheres are connected through fiber inter hemispheric, mainly by the Corpus Callosum. This brain interconnectivity allows a constant interaction within each hemisphere and between both hemispheres, and in this way is intended to adapt responses globally and dynamics (Hernandez-Muela, Mules and Mattos 2004; Poch, 2001).

It is thus that the brain works in a coordinated manner and analyzes the world in a global way, for this reason, when you read something is to understand the letters that make up each word, understood the meaning of each of the words of a sentence, however, these processes are not synthesized independently, but that a general sense is given to each phrase. This is possible thanks to the coordination between each of the lobes of the brain, this is the engineering of the brain, which that allows you to interpret the world and the same design a spacecraft that learn the abc. East the working tool when it comes to learning, and modify their connections, is the final triumph of the teaching. 

It has be found at the same time, another important aspect that is modifiable during critical periods: cerebral laterality, this is expressed in three aspects: anatomical symmetry, unilateral functional differences (as the location of language, speech and analytical processing in the left hemisphere, and temporo-spatial skills, as those related to music and the emotional and humorous repertoire (right) and contralateral sensorimotor control, in this way, understand the functionality of the brain in these three aspects is essential to understand the processes that take place in the reorganization of the brain during the learning process because it is a very rich source of experiences that can benefit education (Maciques, 2004).

References:

 Aguilar, F. (2003) Plasticidad cerebral: parte 1. Rev Med IMSS. 41(1) 55-64.

Avaria, M. A. (2005)  Aspectos biológicos del desarrollo psicomotor.  Rev. Ped. Elec. [en línea] Vol 2, N° 1.

Deacon, T. (2000) Evolutionary perspectivas on language and brain plasticity. Cognitive science. 28 (1) 34- 39.

Hernández-Muela, S., Mulas, F. y  Mattos, L. (2004) Plasticidad neuronal funcional Rev Neurol. 38 (Supl 1): S58-S68.

Maciques (2004)  Plasticidad Neuronal. Revista de neurología. 2 (3) 13-17.

Poch, M.L. (2001) Neurobiología del desarrollo temprano. Contextos educativos. 4. 79-94.

Tubino, M. (2004) Plasticidad y evolución: papel de la interacción cerebro – entorno. Revista de estudios neurolingüsticos. Vol. 2, número 1. 21-39

Verquer, K. & Junqué, C. (2000) Recuperación de las lesiones cerebrales en la infancia: polémica en torno a la plasticidad cerebral. Rev Logop Fon Audiol. XX(3):151-157.

Walsh, T. M. & Diller, K. C. (1981) Neurolinguistic considerations on the optimum age of second language learning. En. K.C. Diller (Ed) Universal in language learning aptitude USA. Rowley: Newbury House Publishers.

Woods, B. (1980) The restricted effects of right hemisphere lesions after age one: Wechsler test data. Neuropsychology. 18: 65-70.