The importance of the environment in brain development

If we stops the study of learning stops only on genetic researches, thinking that we born born with immutable physical and cognitive structures, given from the moment of conception, we can believe environment is not so important, however, contemporary genetics and studies on the human genome, provide novel approaches to the source, and explain many pathologies, giving  more and more place to the experience of the individual and corners to a very precise place to initial genetic determinism that held  few years ago.

 

This suggests the possibility that brain superior functions are based on a biological substrate clearly designed by the genome, but the deployment and development of such capabilities of cognitive abilities need essentially the influence of the environment so much so that, without it, these functions may be severely truncated.

In this sense, it is known some regulatory genes susceptible to light only if they receive certain environmental signals, thereby greatly the generation of synaptic connections and neural routes are not provided in the basic design that are unique to each individual in relation to the experience.

But how does this relate with our brain?, well, as already mentioned, the human nervous system perceives, processes, stores and create behavior in response to information received from the environment, internal and external with the ultimate aim of ensuring the conservation of the species, that learning is as important as a means of stability, since the key brain capabilities level to develop skills for individual survival (Avaria, 2005).

At the end, our nervous system is the supporting material for knowledge, affection and behavior, along with genetics, and skills will be developed for adaptation in the middle which will make us more or less able to respond to the needs of the environment.

Of course is not possible to forget the role of our genetics heritage from parents, so there is something called genetic imprinting which is a phenomenon where certain genes are expressed in a way specific, for example, if a parent inherits more genes with certain features that the other is put in risk the brain and behavior of children, resulting in several possible syndromes.

 

Some research found out that gene expression plays an important role in brain development, in a way such that certain regions of the brain are almost entirely controlled by the genes of the mother and other regions, by the father (Wenner, 2009).

But once the environment comes in the sequential and orderly development of the nervous system gives rise to a fundamental concept, known as either critical periods and sensitive periods . 

This concept refers to the existence of determined moments in the maturation of the nervous system that establishes the conditions to achieve a particular function, what is really important in this aspect is that if the structures related to a function remain deprived of the necessary environmental influences for its development, this not will develop properly, even if these influences can exert their action at a later period. 

This knowledge came thanks to classical studies which showed that if it was blocking an eye of a kitten during their first weeks of life, this caused irreversible loss of vision in that eye due to the decrease in synaptic inputs to cortical neurons from thalamus (Hubel & Wiesel, 1970). 

These studies led to think that childhood was the only time critical development, but further investigations, particularly those carried out through neuroimaging, for example some at the University of California in los Angeles and at the National Institute of Mental Health in Maryland, allowed to observe a second stage of growth of gray matter just before puberty during which, our brain develops different to early adulthood. Analyses show that the maturity of the grey matter, is not signal the end of mental changes, but the ability to re settle and rearrange if same and that this occurs during adulthood as a signal of the continuing brain development for several years, being a reflection of the environmental interactions (Shreeve, 2005).  

This topic has received great attention, not only from the scientific community, but also on the part of the media and the community in general, developing related term of windows of opportunity, with important implications from the point of view of education, especially preschool. 

A well-studied aspect in this regard relates to the acquisition of language, since it is thought that learning a foreign language is only possible prior to puberty. However, studies with bilingual populations have shown that learning is possible, but it is  acquired with some grammatical errors and a notorious difficulty in the structuring of phrases, as well as an accent.

Positron Emission Tomography (PET) have shown that if a baby learns a second language, all linguistic activity is located in the same area of the brain, while those children who learn a second language later show two focuses of activity. Some studies in this respect have found in English speakers a curious decodification if the sounds R and L in separate parts of the brain, but these sounds are processed in the same part of the brain in those whose mother tongue is Asian because these languages do not distinguish between these phonemes (Kim, Relkin, Lee. Et all., 1997; Chugani, Phelp & Mazziotta, 1987).

 

In this sense, the possibility of inducing a greater number of connections and synapses through stimulation techniques has been subject of much debate.

One of the attempts that has received a lot of attention  called Mozart effect,  citing positive effects on cognitive abilities and therefore a better overall performance of the individual against multiple tasks. 

However, a recent review concluded that there is a specific improvement in the performance of visuospatial abilities after hearing some pieces by Mozart, but this effect has a short duration, no more than 10 to 15 minutes, which minimizes management commercial that promotes the rapid achievement of higher child intelligence (Avaria, 2005;  Rauscher & Shaw, 1995; Chanda, Levitin, 2013).

 

Other studies analyze the influence of the environment  and have focused on the development of gross motor skills, and what has been found is that this does not require so much stimulation from the environment, so the delay is usually due to biological causes, making it the exception to the idea of the environmental stimulation. 

While there is a normal variation in the acquisition of the development in gross motor development milestones, and the acquisition of the walking skills, this variation is lower than in other areas. This was demonstrated in a study in 404 children with retardation motor, at 18 months, a third of them children had failed to take 5 steps independently, and eventually presented a pathology (Avaria, 2005)

Studies of children with cerebral palsy, have allowed to observe the delay engine in any of its forms, while infants show cognitive delay, thus found with gross motor development within expected is not guarantee of normal cognitive development in the future.

Against, children with mental retardation, in general acquire progress independently at later ages that children with normal intelligence, but within each level of mental retardation, there are children walking to comparable to normal ages. In this sense, a study reported that only 62.2% of children with severe mental retardation and 38% of those who have moderate deficiency, walking after 12 months, showing that motor development may be apparently normal the first year of life, but cognitive retardation will be significant later in this population (Avaria, 2005).  

So we can say, different motor behaviors allow to relate the maturation of cognitive process and the brain connections product of environmental interaction, for example the use which makes the child's hands in relation to the exploration of the environment. 

The analyses that are made about the disappearance of primitive reflexes and maturation of visual function, when the nearby can be focused and achieved simultaneous information on the sight and touch, which establishes the basis of future skills visomotoras which gives opportunity that infant use your hands around three months together. It is so from the 3 to the 6 months baby gradually accomplished prehension voluntary and visually guided, first on the flat side and then in the middle line.

The acquisition of this skill, allows the study of the inter hemisferic-dominance (being right-handed or left-handed) which is not developed until after the first year, and is defined until after 2 years.

Therefore, the handling of objects reflects a progressive understanding of the world that surrounds the infant. At 9 months the child examines the objects in a systematic way, thanks to the ability to process non-sequential and simultaneous information how did before developing this skill.

 Of course this is very important as cognitive development, since around 9 months  will be handling the sense of permanence of objects that demonstrates the symbolic objects representation and causation from the Piagetian point of view, but confirm the consolidation of brain connections that allow such processing (Avaria, 2005;  Bloom, Beal & Kupfer, 2006).  

In regards to the development of the communication and language, this area is where the debate on the relative importance of biological and environmental mechanisms in its development has received greater attention. The question if cognitive abilities such as language are the result of structures and genetically coded and specific predispositions?. 

It is thus that the abilities that children acquire during the development are not only of maturation at the neurological level, but are largely the result of the interaction with the environment. The greater the stimulation that receives, more complete is the neurological organization and better expectations for cognitive skills. In that sense, importance early stimulation in early childhood (Ginarte, 2007).

But those who defend the genetic position can add one more aspect to the discussion,  and it is the role of the genetic influence, particularly the studies on the genetic imprint, since these studies are that the influence of paternal genetics plays a greater role in instinctive as feeding behaviors or look for couple, while the maternal genes are concentrated in the development of cognitive processes such as language and social behaviours (Wenner, 2009). 

The main response in this regard says: if the brains of children are innately predisposed to learn the language, with the proper exposure all children with normal brains must, without instruction, learning the language in a relatively uniform manner. 

If this hypothesis is correct, the capacity to acquire language should be both anatomically and functionally autonomous of other capabilities, and developing lesions or acquired can deteriorate, but does not stop the process of acquisition, on the other hand specifically preserve the ability to learn language. 

If we accept the position that learning of language ability is not innate, instruction should be required to learn it, the course of the acquisition should vary considerably in each person (perhaps depending on the quality of the instruction), and therefore there should be no critical period for the acquisition, or the functional or anatomical specificity of the language (Stromswold, 1995).

At this point, I can't avoid mention a classic study in  conducted around 1960 by Diamond, this experiment analyzed the changes in the structure of the nerve cells in the cerebral cortex of rats when they are exposed to what she calls an enriched environment or an environment depleted . 

 Rosenzweig (cited in Aguilar, 2003) conducted experimental studies in animals, with an idea of possible applications in human rehabilitation field. He proposed enriched environments in a model with rats, living in cages with a number of toys and other stimuli induce changes morphological, physiological, neurochemical and behavioral.

 This  was named as enriched environment if the rat had a large cage and access to objects with that play and explore and also socialize with other 12 rats. The objects had to be changed periodically so that the challenge was greater. The impoverished environment was a small cage with a single rat, without friends or toys (Diamond, 2001).

This experiment found out that animals exposed to the enriched environment had developed cerebral cortex thicker than rats that were in the impoverished environment. The dendritic branches in cerebral cortex had grown as a result of interacting with other rats and explore and play with objects, changes were observed primarily in visual, motor and the frontal area, associated with socializing. They also found low levels of neurochemicals associated with stress.

This study concludes that when nerve cells are stimulated by new experiences and exposure to the incoming information from the senses, it’s possible to grow dendritic branches. If rats continue in a rich in the right environment, the branches grow and this creates greater learning, while in an impoverished environment, these ramifications are pruning  to be lost. 

Diamond (2001) also found something that was not part of the original study, these same rats if were caressed, showed even larger number of neural connections in the area of the limbic system, which is associated with emotions, but also memory. 

They are such situations that make me think that genetics is so important when analyzing a learning problem, what should be the position to a child with Down Syndrome or a child with autism when they have a learning disability?, should we accept the idea of a genetic destiny?, can they learn?. should we believe the theory of enriched environment and say that genetics doesn't matter?. The function of the experience would be, in short, the alter of locally and selective gene expression pattern in charge of the organization and the functioning of a given brain region (Benitez - Burraco, 2006).

Some years ago I learned how to find the right medium of this dilemma. Someone asked during a conference: what is the difference between one and another position at the social level?.

 The answer is that if we accept the genetics, and I think most that most of people accept it, since we change our faces and our voices when we see a child adding a poor boy, he has Down syndrome. Only few persons will  see what this individual is, instead of seeing how this person can be, so we accept the genetic influence as important. 

But if we accept his Down's Syndrome but also this boy has capabilities that can come to be exploited, is to accept the position of the enriched environment.

My question is: How do I know if I have the skills to be high-level pianist if I've never have had the opportunity to be near a piano?. So we should ask: what can I do for this child? Instead of asking: what can this kid do?. It is seeing infants as human beings capable to grow and create and think, and not to fall into the Protocol of applying tons of tests to verify in a scientific way that children have a language problem, or which are not suitable for math or the arts. 

Therefore the vision of the neuroscientific posture is appealing to the brain and its ability to achieve neural connections, based on the skills that you already own to this meet that cost work or is even dreaming of having. Who was found with a good math teacher who managed, that for a moment, we thought that numbers were simple, even to me?. Neuroscience appeals to the principle of flexibility which is called plasticity, to develop skills from strategies that enable each individual better understand reality. 

Each brain develops, grows, learns, observes, understands differently. Some are based on visual clues, others are excellent for understanding the logical way to world mathematics. Some are good to be located geographically, while to others, we have the broken GPS. This is what makes wonderful brain, can be molded plus enjoy this learning, and learning in many ways. The children not only learn by repeating, learn again and again playing with a Nintendo game. Even if adults like or not, children's brains generate neural networks faster than us, take advantage of this window of opportunity is the difference between suffering in school and enjoy school. 

Some lessons require repetition, others require understanding of its usefulness, while others are based on direct experimentation. Cognitive goal tasks needs to recognize and apply the necessary strategies is perhaps the differences between this child cannot learn and this child learns differently .

References:

Aguilar, F. (2003) Plasticidad cerebral: parte 2. Revista  Médica  IMSS. 41 (2) 133-142.

Avaria, M. A. (2005)  Aspectos biológicos del desarrollo psicomotor.  Revista de Pediatría. Electrónica. 2 (1). Disponible en red: http://www.revistapediatria.cl/vol2num1/pdf/6_dsm.pdf 

Benítez – Burraco, A. (2006) Genes y lenguaje. Teorema XXVI (1) 37-71.

Bloom, F: Beal, M & Kupfer, D. (2006) The Dana guide to brain health. Dana Press. Estados Unidos.

Chanda, ML., & Levitin, DJ. (2013) The neurochemistry of music. Trends in Cognitive Science. 17 (4) 179-193.

Chugani, HT., Phelps, ME, & Mazziota, JC. (1987) Positron emission tomography study of human brain functional development. Annals of Neurology. 22 (4) 487-497.

Diamond, M. (2001) Response of the Brain to Enrichment. Anais da Academia Brasileira de Ciencias. 73 (2). 39-45.

Ginarte Arias, Y. (2007) La neuroplasticidad como base biológica de la rehabilitación cognitiva. Geroinfo: Publicación de Gerontología y Geriatría 2 (1) 1-15.

Hensch, TK., and Billimoria, PM. (2012) Re-opening windows: Manipulating critical periods for brain development. The Dana Foundation. Disponible en red: http://www.dana.org/news/cerebrum/detail.aspx?id=39360

 

Hubel D., Wiesel T. (1970) The period of susceptibility to the physiological effects of unilateral eye closure in kittens. Journal of  Physiology. 30 (4) 206- 212.

Kim K., Relkin N., Lee K. et al. (1997) Distinct cortical areas associated with native and second languages. Nature. 388: 171–174.

Rauscher F., Shaw G., Ky K. (1995) Listening to Mozart enhances spatial-temporal reasoning: towards a neurophysiological basis. Neuroscience Letters. 185 (1) 44-47.

Shreeve, J. (2005) Cornina’s brain: all she is… is here. National Geographic. 207  (3)  6-12.

Silverman, C. (2008) The Search for Intelligence. Scientific American.  299  (4) 13-19.

Stromswold, K. (1995) The cognitive and neural bases of language acquisition: The cognitive neurosciences. Cambridge, MA: MIT Press.

Wenner, M. (2009) A patchwork Mind. Scientific American Mind. Vol. 20. num. 4. 52-59.

Brain development; neurogenesis, apoptosis and synaptogenesis

I do not know you but  I find incredible the way that nature uses the energy and resources to create masterpieces, as flowers, honey bees or brains.

An example of this is brain development, since the nervous tissue formation begins with the formation of a simple tube, called neural tube from the neuroectoderma induction (this is part of the ectoderm that is the outermost cell primary embryo that originates the central and peripheral, nervous systems including some glial cells), this process occurs as part of human neurodevelopment between the third and fourth gestational week and wrapped the most fascinating functions that it is possible to imagine.

But the road is not simple, since once formed the neural tube occurs a differentiation in three dimensions: the first leads to the spinal cord, the second will give rise to stem and brain stem and the cerebellum, while the third portion will develop the cerebral hemispheres.

This stage is called a proencephalic process that occurs between the fifth and tenth gestational week and during which an active neurogenesis (neuron development) and this develops from the neural precursor cells, which have a special feature and is not mature and do not proliferate, because it will have to wait for the next moment for such differentiation (Poch, 2001).

Between the eighth and tenth eighth gestational week, occurs an active neuronal proliferation, the precursor cells begin to differentiate to produce new precursor cells and neuronal cells different of neurons and glial cells (astrocytes and oligodendrocytes).

The speed of proliferation in this period that occurs between the 2nd and 4th month of intrauterine life is impressive since they are around 200,000 neurons per minute, as fast as any kind of thought, this cell proliferation, is known as neurogenesis, this process occurs slowly, and after going through several cycles of cell division, this is stopped, since as we know, that in excess is bad.

Even if it is unknown what starts and then stops the mechanism of proliferation in any region, it is clear that the periods are rigidly determined, although we know it depends on neural factors specific to the region of the brain where it occurs and functions to be exercised, by between what 3rd and 5th month occurs the migration of neurons guided by processes glial based on chemical signals and neural growth factors, mediated by regulatory genes that determine the activity of other genes in a defined sequence and for precise periods and in specific regions.

What has already been observed is that differentiated cells begin to emigrate from ventricular areas (Central) to the more peripheral areas of the brain (neocortex) development.

This is a specific order, which begin first occupy the deeper layers of the cortex layers, while those that start later, occupy the uppermost layers.

This radial migration of neurons to the periphery, uses glial cells as a guide since these form a scaffolding that facilitates the movement of neurons. Neuronal migration occurs mainly in two regions in the thalamus and hypothalamus, where the oldest neurons are pushed by more new neurons, by which the first will be located in the periphery. On the other hand, in regions of the brain structure of laminar, as it is the case of the cortex and the cerebellum, neurons more young people migrate to break through to the oldest, whereupon the latter will sit closer of the neuroepithelium and the more young people on the periphery.

Neuronal migration process takes place between the 10th second and the twenty fourth gestational week, but it is noteworthy that not all cells survive since during neurogenesis and neuronal migration, approximately 50% of neurons undergo apoptosis, meaning that cells die in a programmed way, probably because they do not follow the correct course of emigration or because they do not receive the stimuli of the rest of the networks that are created, but the correct answer is still a mystery.

A certain proportion of the neurons that survive (20%) Trek horizontally and one after radial migration, to allow the formation of lamination (segmentation) cortex, it is so neurons looking his way, motivated by chemical stimuli (neurotrophic factors), extending its structure in one of its ends, resulting in the so-called axonal growth cones.

Simultaneously with the neuronal migration occurs in synaptogenesis (formation of synapses), although this is much more intense between the twelfth and the twelfth fourth gestational week, but persists in a very active way until the eighth or ninth month postnatal (Avaria, 2005; Sanhueza, Nieto and Valenzuela, 2004, Sagan, 2003; Poch, 2001).

It is interesting to note that prenatal synaptogenesis is mainly determined by the genetic heritage of the individual. However, in the stage postnatal synaptogenesis is also affected by sensory experiences, particularly by the learning process and the stimulation from the environment.

Neurogenesis and the subsequent stages associated with this process morphogenic lead to the formation of approximately 100 billion neurons in the adult brain and several trillions of synapses. This implies that a significant number of the 30,000 genes that we have must be involved in this complex process, expressing together in simultaneous or sequential form.

However, she has still not been achieved understand this prodigious process, because a region possessing 20,000 genes, is only 302 neurons and nerve tissue that form is far from having the functionality of the human brain (Sanhueza, Nieto, and Valenzuela, 2004).

So as a result of the differential expression of genes in the course of time, and in different cells of the embryonic structures, given the development process, but this depends on much more than a base sequence of the genome and the history and composition of the genome of the parents.

While the genome gives specificity and individuality that new body, its expression depends not only on bases of DNA, but also the protein and environmental environment in which it is (Vasquez Laslop and Velázquez Arellano, 2004).

As son as intrauterine development finish, we see the birth of a new human being, but even it is true that the neural cells are there, ready to connect with each other, will take between 2 and 3 years until they manage to do it logically, because the relationship between them depend on the needs of the environment.

When brains of the babies are ready to see the light,  they work but they are very immature, partly because the brain needs lot of flexibility to adapt and reply to the environment. This prevents them from performing tasks that other mammals in a few days or weeks after birth, for example, human babies require much effort to set the look, or control the trunk to sit. However, are born with reflexes that will enable them to adapt to the new environment, as a reflection of suction, that will give you food that requires to help its development, although there are others like blinking and crying that will provide you the opportunity to have contact with caregivers (Quintero Gallego, Manaut, Rodríguez, Pérez - Santamaria and Gómez, 2003) .

The number of cells in the fetal brain is between 30 and 70% higher than the number of neurons in the adult. Surplus cells survive for a period of days to weeks, after which, on its own, starts a cascade of degenerative changes and a physiological process of programmed cell death. In the picture below, it is possible to observe the differences between birth and two years of development, although it seems that increased neuronal tangle, in reality there are what are they are less neurons with larger number of neural networks, connections between neurons, i.e. interneuronal communication, which allows a more robust network that ensure more specific skills.

In this sense, found that the selective removal of the synaptic connections, is a fundamental process in the cognitive development of the child, as has been observed relationship between changes in the gray matter of the frontal lobe and the evolution in the performance of cognitive tasks (Chapel, Romero, Maestu, field, Fernandez, Gonzalez Marquis, Fernandez and Ortiz, 2004;) Hubel and Wiesel, 1970).

At this point, important thing is to start the race to connect to neurons. Although the neuronal pruning will be inevitable, since this is a process of survival of the fittest under the Darwinian principle that everything that is not used is discarded, neurons that fail to create medium-term goals that enable adaptation, they will be destroyed, the important thing for the brain is to achieve the process critical enabling that new creature to make it into the world. The critical process will be listening, see (to later make discrimination environment and information) stand up, little by little to control their own weight (around the year of born), recognize the natural mother language  for later use it to communicate and finally walk.

Some say that the first two years are the most important for the education of children, and there are those who insist that math, music or foreign languages are important in this critical period of development, however, there is no evidence that this is vital for the process of cognitive development, because they can be perfectly learned once the most important process occur.

What is achieved with this is process of brain, organization which begins six months of gestation and lasts throughout life. Although the rhythms vary, thus, as already mentioned, during the last trimester of pregnancy and the first two years of life, the pace of organization is quickened, then becomes less rapidly to 10 years of life, to continue so slow during the rest of the life.

During the acceleration phase, occurs a large increase of dendritic extensions and small branch, which has been called dendritic arborization, that form numerous synapses, so that all cells and its extensions are arranged in layers and orient themselves, at the same time causing programmed cell death and differentiation and specialization neuronal, this depending on the interactions with the environment and genetic factors.

So crests of the neuronal branches are, density peaks occur at different ages, but also in different brain areas. Thus one fast and dense development both in the visual cortex and the hearing between the 3 and 4 postnatal months and maximum density, around the year of life can be observed. Against, the growth of the prefrontal area is presented at the same age, but the peak is reached until after the first year of life.

The only exceptions are the granulated cells of the olfactory bulb, cerebellum and hippocampus, which continue its genesis after birth and continue for life (León Carreón, 2003).

However, there is also a regressive phase, which presents a selective loss of synapses, this occurs after periods of great intensity. In the same way that the synaptic formation crests, decreases the time of reduction varies between different regions, for example, the visual cortex synaptic density, between 2 and 4 years, while the prefrontal cortex, takes place between 10 and 20 years of age approximately (Poch, 2001).

These periods coincide with the stages of cognitive development widely explained by Jean Piaget, if the stages of brain development, equate either dendritic arborization of the gray matter development, coincide with the periods marked for cognitive progress. From both positions, the environment will play a leading role, but in the case of brain development will be added, intrauterine infections, chromosome pathologies or nutritional deficits that may directly affect the development within the mother's uterus.

Myelination, (which is an overlay of the neural connections by a specialized membrane that allows a proper transmission of nerve impulses), is essentially a post natal process, occurring in cycles, with a default orderly sequence that contributes greatly to improve the functionality of the brain because it produces an increase in the speed of nerve impulse conduction.

In this sense has been found that there is an increase in white matter during childhood, which probably reflects the increase in myelination (Quintero Gallego, Manaut, Rodríguez, Pérez - Gómez and Santamaria, 2003;) Chapel, Romero, Maestu, field, Fernandez, Gonzalez Marquez, Fernandez and Ortiz, 2004; Avaria, 2005).

However, this process, as well as the maturation process, occur at different times, in particular found that the projection areas, mature before the associative, so the latest in purchasing a myelinated appearance are frontal parietal and occipital lobes (Quintero Gallego, Manaut, Rodríguez, Pérez - Gómez and Santamaria, 2003; Chapel, Romero, Maestu, Campos, Fernandez, Gonzalez Marquis, Fernandez and Ortiz, 2004; Avaria, 2005).

References:

Avaria, M. A. (2005)  Aspectos biológicos del desarrollo psicomotor.  Revista de Pediatría. Electrónica. 2 (1). Disponible en red: http://www.revistapediatria.cl/vol2num1/pdf/6_dsm.pdf

Capilla, A.,  Romero, D.,  Maestu, F., Campo, P., Fernández, S., González Márques, J., Fernández, A. y Ortiz, T. (2004) Emergencia y desarrollo cerebral de las funciones ejecutivas. Acta. Esp. Psiquiatr. 32 (2) 377 – 386.

Hubel D., Wiesel T. (1970) The period of susceptibility to the physiological effects of unilateral eye closure in kittens. J Physiol. 30 (4) 206- 212.

León Carrión, J. (2003) Células madre, genética y neuropsicología. Revista Española de Neuropsicología. 5 (1) 1-13. 

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

Quintero Gallego, E., Manaut, E. , Rodriguez, E., Pérez – Santamaría, J.,  y Gómez, C. (2003) Desarrollo diferencial del cuerpo calloso en relación con el hemisferio cerebral. Revista Española de Neuropsicología. 5 (1) 49-64.

Sanhueza, J., Nieto, S. y Valenzuela, A.  (2004)  Acido docosahexaenoico (dha), desarrollo cerebral, memoria y aprendizaje: la importancia de la suplementación perinatal. Rev Chilena Nutrición. 31 (2) Disponible en: http://dx.doi.org/10.4067/S0717-75182004000200002 

Sagan, C. (2003) Los dragones del Edén: especulaciones sobre la evolución de la inteligencia humana. Barcelona. Crítica.

Stromswold, K. (1995) The cognitive and neural bases of language acquisition: The cognitive neurosciences. Cambridge, MA: MIT Press.

Vásquez  Laslop, M. y Velázquez Arellano, A. (2004) Genómica y el desarrollo de un nuevo individuo. En A. Velazquez (2004) Lo que somos y el genoma humano: des-velando nuestra identidad. Ediciones científicas universitarias. UNAM. FCE.

Genes and genetic disorders

If we think about how amazing it has been  the Human Genome project, how much we have learned from it and everything that has been generated so far, it's impossible to ignore the value of genomics, for example,  initially was thought that our 46 chromosomes were composed of 100,000 protein-coding genes, enzymes, hormones and overall regulatory sources of all life processes that shape human characteristics but now is possible to begin to manipulate all of them  to heal syndromes and diseases.

Chromosome 22 was the first to be fully identified 545 genes having assets, followed later by genetic mapping or sequencing of chromosome 21, with only 225 active genes, which opened the possibilities for genetic treatments medical situations as Down Syndrome, a form of Alzheimer's disease and various cancers.

Thus began the race to find a specific gene for each of the major conditions that afflict humans. At the same time, it have been found the relationship between the production of proteins and some genes that create on protein production and others that inhibit the production of the same.

In this sense it was found some genes associated with autism spectrum syndromes such as 15q11-q13, 2q37.3 or UBE3A for Angelman syndrome, which has also been associated with the GABRB3 gene, whereas for the syndrome Williams is the gene 7q11.23; MeCP2 for Rett syndrome, to mention only the best known developmental syndromes.

However, it is known that there are more syndromes, such as West syndrome that is associated with the ARX gene, or even lower prevalence may be mentioned De Lange syndrome or Crohn's disease, whose genetic alteration is in 5p13.1 gene.

Talking about less common syndromes we can talk about Smith-Magenis syndrome which is associated with  17p11.2 gene, or the VCFS 22q11 gene related, with myotonic dystrophy which is a multisystem disease whose genetic alteration is associated with the repetition CTG trinucleotide on chromosome 19.

While the tuberous sclerosis complex (TSC), which is an autosomal dominant inherited disease which may be due to the mutation of two distinct genes: TSC1 (9q34) and TSC2 (16p13.3).

Timothy syndrome caused by a mutation in the gene CACNA1C located in 12p13.3, other forms of alteration as 10p terminal deletion, has been associated with a phenotype similar to DiGeorg syndrome causing hiccups hyperparathyroidism, deafness sensory abnormalities stones.

Moreover, it has been  studied the gene involved with 45X/46XY mosaicism, or we can mention Cowden syndrome is associated with PTEN gene, which is located at 10q23.3.

Another group of genetic disorders like Goldenhar syndrome are related  to deletion 5q (Artigas-Pallares, Gabau-Vila & Guitart-Feliubadaló, 2005), all associated with developmental disorders.

Whereas if you look at the studies on cancer have been found, for example for brain cancer, NFkB protein with much higher activity than in normal brains or HER2 protein in lung and breast cancer, BCR- AB1 for chronic myelogenous leukemia, RAS, for several types of cancer, B-RAF for skin cancer, BCL-3 for lymphoma; RB1 for retinoblastoma, HNPCC for colon cancer and endometrial, the p53 gene causes cell suicide and is associated with cancer of the lung, colon, breast and brain (Collins and Barker, 2008).

It's not possible to forget disorders of cognitive processes such as Alzheimer's,  so it's possible to find genetic associations with cognitive processes, although further studies are not conclusive, for instance mentioned the IGF2R gene associated with intelligence, which is a very popular topic.

That is why around 1980 Dr. Plomin, from Institute of Psychiatry, at London, England, began his research on genes and intelligence relationship, since observed that two people with the same genes correlate as much as the same person performing an intelligence test with a year of difference, so he realized that identical twins who live apart are very similar or identical in intelligence tests that identical twins who live together, which is why it is considered that the environment influences the development of children, however it has become clear that genes can shape the brain in ways that make individuals better or worse to answer an intelligence test.

Despite this, Plomin suspect that more markers are needed to find the genes for intelligence, but states that exist many difficult to replicate details to affirm conclusively that have these genes (Silverman, 2008).


More consistently it was found the  called language gene, which from the genetic standpoint is associated with the specific disorder of the cognitive process, which seems to be due to alteration of a small number of key genes and in particular FOXP2 gene mutation.


The gene in question is expressed primarily in certain areas of the central nervous system, both during embryonic development and in the adult individual, but is also expressed in other regions during embryo development, such as lung, intestine and heart, and in different tissues of the adult. However, affected individuals with language impairment, have a non-mutated copy of the gene (Burraco Benitez, 2005; 2006; Gopnik and Crago, 1991).


Although each day is more advanced in the study of genes and the proteome, considering that it is estimated that there are about 4000 genetic disorders, and so far has been identified only a little more than 60 genes involved in diseases, no doubt the work will take several years before conclusion, but in spite of all the implications of research some point that knowledge of the human genome will be the main focus in the diagnosis and treatment for a large number of diseases such as diabetes, cardiovascular disease, mental and many forms of cancer.

References: 

Artigas-Pallarés, J., E. Gabau-Vila, E., Guitart-Feliubadaló, M.  (2005) El autismo sindrómico: II. Síndromes de base genética asociados a autismo. Rev Neurol. 40 (Supl 1): S151-S162.

Benítez – Burraco, A. (2006) Genes y lenguaje. Teorema Vol. XXVI/1, 37-71.

           

Benitez-Burraco, A. (2005) FOXP2: del trastorno específico a la biología molecular del lenguaje. I. Aspectos etiológicos, neuroanatómicos, neurofisiológicos y moleculares. Rev Neurol.  40 (11): 671-682.

Collins, F. and Barker, A. (2008) Mapping the cancer genome. Scientific American Special Edition: New answers for cancer. Vol. 18. Num. 3. 22-29.

Gopnik, M. y M. B. Crago (1991) Familial aggregation of a developmental language disorder.  Cognition. 39. 1-19.

Hayden, KE., Strome, ED., Merret, SL., Lee, HR., Rudd MK., Willard, HF. (2013) Sequences Associated with centromere competence in human genome. Molecular and Cellular Biology. 33 (4) 763-772.

Weischenfeld, J., Symmons, O., Spitz, F.,&  Korbel, J. (2013) Phenotypic impact of genomic structural variation: insights from and for human disease. Nature Reviews Genetics. 14. 125-138.

 Young, E. (2013) Shutting down the extra chromosome in Down's Syndrom cells. National Geographic: Phenomena: Not exactly rocket science. Disponible en: http://phenomena.nationalgeographic.com/2013/07/17/how-to-shut-down-the-extra-chromosome-in-downs-syndrome/

The human genome

Following our little story about DNA, after the first research that explained the composition of this called molecule of life, researchers continued trying to understand the genetic makeup of human beings.

Something clear after the first findings about normal human genome, it's the fact this consists of 23 pairs of chromosomes, those inherited by mother andthose inherited by  father, but in total there are 24 pairs of chromosomes since  2 correspond to the sexual chromosomes X and the and, Y which harnessed on XX if you are female and XY if you are a male.
 

This is part of the working material of the genetic, which is responsible of researching  heritage and vulnerability of specific the genotypic traits and the genes associated with them. On the other hand, the new science called  Genomics sees genome as a whole, even their multiple interactions with environmental factors, resulting in perceptible all the individual organism. For this purpose it has methodological tools that allow you to study at a time, globally or in parallel, a single biological sample, thousands of genes or their products (Velázquez, 2004).

These gene sequences control most bodily functions and structures, such as the creation of organs, connection between  neurons in the nervous system, skin color, color of eyes, etc.,  however, in order to those genes exert their specific action is required in addition to their structural and functional integrity the presence of a suitable environment. 

Other two fundamental genetic concepts are genotype and phenotype, the first refers to an individual's genetic constitution is  genome specific to an individual, in the form of DNA, while phenotype refers to what is related with  apparent characteristics as  factions,  color of eyes,  timbre of the voice. Then we can say,  genotype can be defined as the set of genes of an organism and the phenotype as a set of traits of an organism.

So the generation of  diversity of races and physical features is  made by a genetic recombination which undergoes each generation, but each individual is genetically different from everyone else (except if you have an identical twin), since the variety of ovules  or sperm that are formed along the life is so great, for practical purposes  only can say that none of them is equal to the other. Thus, mutations are the specific material of genetic diversity, but is is even greater and less controllable in species with sexual reproduction, which constantly faces  different genomes.

Genome (is a word made up of genes and chromosome) and is the totality of genetic material of an individual that contains the information for the operation and the development of a new body, since the ovule  is fertilized by the sperm until the end of life (Kaessmann & Pääbo, 2002; Velázquez, 2004).

With all that  information emerges with its own light the Human genome project (HGP), which constitutes the greatest scientific adventure of human biology and the genetic map  known. Through this project now we know an important basis of the medicine of the future. 

The Human Genome Project is an international research  whose ultimate goal is a complete description of the human genome, through DNA sequencing. It is known that the human genome consists of 3 billion base pairs, which can be comparable to an encyclopedia composed of thousand volumes, each with a thousand pages and 3,000 letters per page. If the bases would be the letters; the genes are the words and phrases,  while the chromosomes would be different volumes of the encyclopedia. Once completed the sequencing of the human mitochondrial genome, the next step was   investigating the nuclear genome. Given the scale of the effort that goes into the project, it represents what this is the first project of great science in biology (Velázquez, 2004).

But all this sequence is not easy, since the term human genome is used to describe all of the genetic information (DNA content) of human cells. In fact, encompasses two genomes: a complex, nuclear genome, and a simple, mitochondrial genome.

Research shows that nuclear genome  contains more than 99% of cellular DNA, has a total of 3000 Megabases (Mb) which are distributed among 46 chromosomes, 22 different autosomal pairs and two sex chromosomes, which can be distinguished through the application of chromosome banding techniques.

The number of genes containing the nuclear genome is estimated in a range that ranges between 30,000 and 150,000. While the human mitochondrial genome is defined by a single type of DNA. Its nucleotide sequence has already been fully established and consists of 16,569 base pairs in length that contain 37 genes. Unlike its nuclear counterpart, the human mitochondrial genome is extremely compact, approximately 93% of their DNA sequence is coding.

 In the nuclear genome, the percentage of coding DNA is only 3%, the remaining 97%, whose importance is a cause for controversy, it has been improperly called Junk  DNA. But, he found, however, that plays a key role in the normal function of the genome, the repair and regulation, and perhaps even in the evolution of multicellular organisms. On the other hand, public and private human genome project drafts have revealed that all human are identical in 99.8% (Glusman, Sosinky, Ben-Asher, Avidan, Sonkin and Bahar, 2001). 

But the effort to decode the human genome, has been an adventure that has been possible at different stages. The first began in the 1950s, when James Watson and Francis Crick in 1953 discovered the helical structure of DNA.

 Later multiple researchers are added with discoveries key as the Paul Berg and collaborators, who in 1972 created the first recombinant DNA molecule, and scientists from Harvard University and the United Kingdom developed a technique for sequencing DNA.

 In the Decade of the 80s in a joint effort between the universities of Stanford, Utah, Japan and other countries proposes a method for mapping the entire human genome. A genetic map consists of several genetic markers located nearby, one of whose order has been able to determine along each of the chromosomes, as a physical map, which becomes an enormous collection of small chromosome fragments also sorted according to its relative position in their corresponding chromosomes. 

After that, efforts focused on which markers and in which order they are in each one of the fragments of the physical map, similar as pieces of a puzzle, if two fragments share one or more genetic markers, this indicates that the two fragments are contiguous. Thus the genetic map to know the order that saved between if the fragments of the physical map (Velázquez, 2004).

With the development in 1985 of PCR (polymerase chain reaction) by Kary Mullis and his  partners to replicate DNA,  different studies were performed to sequence models of micro-organisms. But it was until 1995 that was published genetic mapping of the first living organism: Haemophilus influenzae which consisting of 1740 genes. This technique aims to obtain a large number of copies of a particular DNA fragment, on the basis of a minimum; in theory just starting from a single copy of this original fragment,  it's possible to amplify a fragment of DNA.  Its utility is so huge because  after amplification, it is much easier to identify with a very high probability of disease-causing by bacteria or viruses, identify people (bodies), or do scientific research on the amplified DNA (Bartlett & Stirling, 2003).

References: 

Bartlett, D. & Stirling, H.  (2003) A Short History of the Polymerase Chain Reaction. Methods Mol Biol. 226:3-6.

Glusman, G. Sosinky, E., Ben-Asher, N. Avidan, D. Sonkin, A Bahar, D. (2001) Sequence, structure and evolution of a complete human olfatory receptor gene cluster. Genomics. 63: 227-245.

Kaessmann, H. & Pääbo, S. (2002) The genetical history of humans and the great apes. Journal of Internal Medicine. 251. 1-18.

National Human Genome Research Institute (SF) A brief history of the Human Genome Project. Available at: http://www.genome.gov/12011239

Velázquez, A. (2004) Lo que somos y el genoma humano: des-velando nuestra identidad. Ediciones científicas universitarias. UNAM. FCE.

Strathern, P. (1999) Crick, Watson y el ADN. Siglo Veintiuno Editores. España.

Watson, J. (2000) La doble hélice. Alianza Editorial. Madrid.