From ancient times, the function of the brain has intrigued mankind; it was easily apparent that a blow to the head caused various disturbances, from a transitory loss of consciousness to a long lasting loss of abilities like speech or movement.

Contemporary science has, among other achievements, discovered the role the brain plays in controlling human behavior. Thanks to this new knowledge, it has been possible to treat afflictions, which for centuries had appeared incurable.

By means of slow and aciduous research, we have discovered a number of cerebral functions, and have discarded numerous old beliefs, which had previously been insurmountable obstacles for medicine. It has been well known that all the cells of our body continually undergo change, but we have recently discovered that brain cells do not reproduce. Brain damage is irreperable. Nevertheless, by analyzing how the brain works, we have discovered that a complex behavior is controlled by various parts of the brain, and that if one of them is damaged, it is possible, through adequate rehabilitation, to place the behavior under the control of other areas of the brain. In fact, just by observing the daily life of people who lose some sense, for example blind people, we conclude that another sense organ can replace a lost function. The blind quickly learn to make use of their tactile senses in place of vision. The impressive case of Helen Keller shows us how extraordinary the acheivements of this kind of procedure can be.

However, it is typical of science that it overlooks simple observations that could lead to important discoveries. For an observation to be useful, it must take place in context with other knowledge. For example, the observation about substitution of one sense for another is difficult to make use of in the rehabilitation of paralytics, since only recently has it been known that the movement of our extremities is controlled by specific sense modalities, and are susceptible to substitution by others. By means of sense substitution it is now possible to help those who have suffered paralysis to move. It is also possible to help the blind guide themselves not only by means of touch and sound, but through light stimuli which can be transformed into tactile sensation.
Currently, with new techniques, we can even see the functioning of the brain.

Since nerve cells consume energy, and this energy is carried by the blood, it is possible to register the flow of blood to those areas of the brain which are activated by particular acts, giving us a kind of window for the observation of the brain as it works controlling behavior. Functions, seemingly beyond our physical grasp, such as thinking, can be studied with these techniques.

To present a full panorama of our work on brain functions would require a great deal of time and space, so we will offer here only brief illustrations of cerebral activities with a few examples of how the nervous system participates in some human behaviors.

Dr. Jorge Juarez discusses the gendered brain. That men and women have distinct cerebral morphologies should not surprise us, not only because the female and male bodies are different in many animals as well as in human beings, but because it has been discovered that the brain is a dynamic structure which changes plastically according to the activities in which one is involved. Just as muscular mass increases with excercise, in the same way cerebral organization varies according to the type of activity one engages in.

For example, years ago a researcher discovered that the thickness of the cerebral cortex changed in laboratory rats according to the amount of stimulus in their environment. Just so, we can observe that environments poor in stimulus contribute little to the development of human beings. Activities undertaken by men and women in our society are different, just as other male and female animals undertake different activities. The brain forms itself in a distinct manner to regulate the hormonal cycles of females and child raising behavior.

All of our adaptive behavior is based on three essential capacities. The ability to focus on important stimuli, to pay attention to anything that might have a bearing on our survival, or make our lives more attractive; the ability to learn from experience and thus make changes in our environment; and the ability to remember experiences and use them in similar situations. In other words, the processes of attention, learning, and memory are fundamental to living beings.
The lack of attention, or extreme distraction can be dangerous, if we are not alert to threats or to things in the environment that might be useful. Many children have learning difficulties, which may be the result of attention deficiency. Knowledge of cerebral mechanisms in this regard may have great impact on future pedagogies. For the layman, this knowledge may impact favorably on his daily conduct. Or think of the stage magician, who depends on distraction to make things appear or disappear, "before our very eyes".

Learning and memory are connected processes. Learning difficulties can make life very limited. The lack of memory can lead one as far as identity loss, as in traumatic amnesia. Currently, a disease which impacts memory directly, Alzheimer,s, has reached alarming proportions among society,s elderly.

A brief review of our knowledge concerning cerebral contributions to attention, learning and memory is presented by Drs. Sergio Meneses, Victor Manuel Alcaraz and Emilio Bumá, for the purposes of showing part of what science has uncovered about these important mechanisms.

Besides examining these basic processes, we take a brief look at more complex behaviors. One essay is devoted to language, thanks to which human beings are able to achieve levels of cooperation which sustain the advance of civilization.

By means of language, individuals are able to appreciate the achievements of others, to transmit the legacies of past societies, and to make plans to avoid future dangers and establish improved living conditions. Victor Manuel Alcaraz examines cerebral control of language behavior to find how words acquire their meaning, and how certain language difficulties in human communication occur as results of brain damage.

But words are volatile, they are lost in the moment they are pronounced, and even if there were means to remember what was heard, it was not until the advent of writing that we had a sure mechanism for recording and transmitting human knowledge. Learning to read and write have become the nucleus of modern education. Regina Martínez looks at the the brain,s role in this new kind of learning.

Finally, we look at aesthetic emotion, part of human experience which has enriched immeasurably our existence. Dr. Julieta Ramos touches on this theme in her contribution with an analysis of the cerebral activity that occurs when we listen to music. We should recall that rhythm has permeated human life not only as an accompaniment of human activities, but above all to enliven festivities, mark the steps of a dance or to intensify religious ceremony. For these reasons, music is a constant of human social life, so that study of cerebral reactions to music serves not only to deepen our understanding of the work of the human brain, but as well to amplify our knowledge of the diverse dimensions of human life.

We hope this "dossier" will help you to visualize some of the mechanisms that direct our activities and awake further interest on your part regarding the workings of the nervous system and its functions.

Victor Manuel Alcaraz Romero

The fact that different types of music can produce different emotional (and physical) states has had an interesting impact in the areas of psychological and physical rehabilitation. For instance, it is known that stimulating music can augment physical energy and induce action, as well as excite emotion. Relaxing, sedate music, of a sustained melody and regular rhythm, with harmonic consonance, has tranquilizing effects, both physically and emotionally.

Gaver and Mandler have proposed that music exists as an interraction between structured sound and a mind which comprehends it. Music has a structure, an objective order of sounds, of a hierarchical nature, consisting of interrelated movements, characterized by melody, harmony, time, rhythmic structure, etc. Another characteristic is the relation between continuity and change exhibited by each piece of music, which determines its complexity. A piece of music without much change is simple, while music with lots of changes is difficult and complex.

We can say with some certainty that the study of language requires a clear determination of all componenents of language. For instance, 1) the motor activities of the articulating vocal aparatus which produces vowels and consonants, 2) the series of sounds which taken together make up the sonoric structure of a word, and 3) the meaning of the word.

When we try to examine the motor of the vocal articulator, we discover that certain body movements are controledby the frontal region of the brain.We arrive at this discovery by means of observation of pathologies demonstrated by people who have suffered damage to certain parts of their brain, as well as by means of animal experimentation.

We now know that the right side of the brain controls the left side of the body, as well as the vocal articulating aparatus by means of which people are able to pronounce words.

Analysis of the divisions in the brain, and study of the specific functions attributable to different parts of the brain, leads us to conclude that the pronunciation of consonants is controlled in the left brain, while vowel production is controled by the right brain.A patient with a lesion in the left brain cannot speak, but can sing.

The construction of meaning of words is more complicated.Thanks to certain inter-cerebralcircuitry, a temporal zone of the brain processes the sounds of words, and apparently assigns meaning.If a foreign word is heard, and the patient does not recognize it, the temporal zone is not activated.If a word the patient knows is pronounced, the temporal zone processes the word, and establishes its meaningful relations . For a word to denote someting, a previously established association is necessary among articulatory acts, sounds, and the sense region in the brain. For example, if there is anassociation between the activated frontal zones (which generates the moror activity which produces the sound "grapes") and the occipital zones of sense excitation (at the sight of grapes), then the word will have meaning.In other words, meaning is the conjuntion ofactivities in the posterior region of the brain which generate auditory reception or vocal production of a word.

Living beings find themselves surrounded at all times by a large number of stimulants (visual, auditory, tactile, olfactory, and gustatory); suffice it for the reader to try to attend to all the stimuli in his environment to get some idea of just how much information we receive at each moment.

The processing of these stimuli depends on multiple factors. One is the level of alertness that an individual maintains, which can go from a coma state, to an anaesthetized state, or a dream state, or to normal vigilance. Within each of these states, there are different levels of alertness.
Looking just at the state of vigilance (normal consciousness), it is not possible to attend simultaneously to all the stimuli which we receive. In 1890, William James, one of the fathers of modern psychology, had proposed that we were only able to give attention to one element within our environment at a time, and that only those activities which we performed automatically, as a result of continual practice, could be undertaken simultaneously. But even in the best of cases, we could not attend efficiently to more than two or three elements within our environment.

It has further been proposed that a principal function of attention is to permits us to select and organize information for the purpose of formulating appropriate responses. Although the selection of sense information is the cognitive process that has been studied most in laboratory experiments, selective attention might imply other, and broader studies regarding, for example, thoughts, memories or motor activities. Also, selective attention takes place in close relation with other cognitive processes; it is a prerequisite for learning and memory, and at the same time is influenced by them and by aspects of motivation and emotion.

We are able to affirm that two of the most important elements in mental attention are the level of alertness and the selection of relevant stimuli. These are intimately related, in such a way that detection of a relevant stimulus increases the level of alertness, while the state of alertness affects directly the efficient selection of significant stimuli.

Direct application of attention studies have produced advances in understanding of learning and behavior problems in children, such as hyper-activity, or attention-span development.

Music is a complex stimulant, which requires sense, cognitive, emotional and motor processes. Although there exist certain cerebral structures which specialize in different levels of auditive processing, the nervous system functions as a whole. It is, clearly, a conjunct of subsystems, each one of which is made up of nerves whih process part of the information received, internally or externally. We know what the sensory auditive channels require to function, but other sense systems function in the perception of a musical stimulus. Musical perception, besides the capacity to hear notes, notes, chords, duration, timber and intensity, requires also the perception of sequential and spacial relations of notes, melody, harmony and rhythm.

Musical experience provokes the participation of numerous cerebral stuctures related with motivation and emotion. Other cognitive processes, like attention, learning and thought, are involved also. Because of this complex of interrelations, the study of musical experience is extremely difficult. We cannot isolate specific structures, but must approach the entire nervous system, and its relations to music, in all its complexity.

The initial processing of the musical experience is related to the experience of sound, which we may define as repetetive changes in the pressure of a medium, normally air or water. It is a vibration of different frequencies, received and codified by the ear and transformed into electrical signals and sent by the auditory nerves to the central nervous system. The information reaches the auditory cortex located in the lateral side of the cerebral cortex (temporal lobe.) Auditory stimuli are received and analyzed in this area. This is where we hear. These areas communicate with secondary areas which process groups of acoustic stimulants which arrive simultaneously, as well as consecutive series of different tones and rhythmic acoustic structures. Penfield and Perot, in 1963, observed that stimulation of these secondary areas could cause musical hallucinations.

Studies of normal people have demonstrated that the right brain predominates in the perception and production of timbre, tone, chords, intensity and musical melody, as well as non-verbal sounds in the environment.

The left brain appears to be related to the perception of sequential and rhythmic aspects of music. In fact, there is a successful rehabilitation program for patients who have lost the capacity for speech, due to a lesion in the anterior regions of the frontal lobe (Broca,s aphasia), involving tonal melodic therapy, and which has helped them reaquire language through song.

The Federal Primary Education System predicts that 10% of the first grade population will not learn to read or write efficiently in the course of the school year. The causes are various. A significant number of these children suffer from sense deprivation "visual or auditory " which will keep them from using the knowledge provided by the schools. Others, in the marginal regions of the country, rural as well as urban, live in conditions unfavorable for the development of adequate instruction for the young.

Malnutricion and lack of Spanish among the indigenous population are also factors which make academic acheivement difficult. In the following pages, I will focus on a group of children who, in spite of adecuate social conditions and no noticeable sense deprivation, do not learn sufficiently to read or write during their first year of primary education.

I will do this, not because the groups with social limitations are unimportant, but because it is necessary to look carefully at the problems of students who "inexplicably" fail to learn. During the 50s, 60s, and 70s, primary school teachers spoke often of "dislexia". This lable was normally used after students had failed their first years of school. At that time, there were few techniques for helping these children, and so it was parents who struggled with these difficulties until their children either recovered or were lost among the statistics of school drop-outs.

For many years, the study of the relation of gender differences and the brain focused on brain size. Claims were made that men had larger brains, or that women,s brains were larger proportionally, if we took into consideration body size. None of this means much if brain activity is understood not in terms of cuantity of neurons, but in terms of efficient use of neuronal connections.

Anatomic differences, or functional differences between men and women demonstrate nothing other than those differences; it is pointless to translate them into any sort of hierarchical superiority. In recent years, more interesting studies have been done with regard to structural and functional sexual differences in the brain.

Gender differences in mammals involve diverse anatomical, physiological, and behavioral aspects: morphological differences in primary and secondary sexual characteristics, physiological and behavioral characteristics related to sexual reproduction, as well as structural and superstructural characteristics of the central nervous system.

Gender differences between males and females make up what is called sexual dimorphism, and are evident in most mammals, as much in reproductive behavor as in primary and secondary sexual morphology. Nevertheless, there are behaviors not associated with reproduction which do not present an obvious sexual dimorphism, which have been studied experimentally. In various species of mammal, we have observed a different emotional response to stressful situations between males and females. It appears that males adapt more quickly to stress, although initially they respond with a higher emotional behavior index than females.

Games are also a dimorphic sexual behavior in primates and rodents. In both cases, males play in a rougher manner than females, (behavior which can be altered by hormone levels). Other behavior, like preference for different flavors, reaction to electrical charge, eating habits and body weight, learning and task execution, as well as response to cerebral damage, are sexually dimorphic and susceptible to hormone treatment at distinct stages of growth.

A spring under pressure will return to its original shape if the pressure is removed; on a baby,s cheek is a mole which appears identical to a mole on its grandfather,s cheek; a dog will run from anyone who bends to pick up a stone: in all cases, the specialists in the respective areas of study will probably use the term memory, in spite of the fact that these are such distinct realities.

Nevertheless, a human being from whatever culture or epoch will manage a generic vocabulary to refer in a specific manner to the process of trying (with or without success) to recall mentally a past event. That is to say, we all have an intuitive and introspective notion of what the human capacity for memory is.

We are conscious that meaning, living thought, resides stored somehow in our brain, and that we can recover and make conscious use of this accumulated knowledge.

The human brain is the most complex structure in the known universe. During millions of years of evolution, genetic inheritance and experience have joined to form different cerebral mechanisms. The great functional result of all this is the mind. It depends on forms of communication established among hundreds of thousands of millions of neurons or brain cells.

This complex aparatus permits each human being to connect with the common past of his species in a particular way, by which he aquires knowledge, retains information over the course of his life, and uses it in a way which allows him to identify himself as an individual different from others.

Learning and memory are two of the cerebral processes by which the individual human mind is created and developed.

The memory is a functional property of networks of cerebral cells based on the plasticity of their interconnections. Almost all forms of activity of these networks leave traces, or lasting "footprints". Thus, memory is something by which the brain is constructed.

Human adaption to the world we live in is the result of the plasticity of our brain. In other words, the nervous system can modify itself and in this way supply new ways of adjusting to the changing conditions around us. When we are born, the structure of our nervous system is specified by our genetic endownment. The nerve cells, called neurons, are related to each other in the following way: A group of neurons specialized in receiving stimuli from the external environment or from the interior of the body, is associated with another group of neurons which is connected to the muscles and produces in them contractions which allow us to walk, manipulate objects, or secrete sweat, tears or gastric juices. The neurons which receive stimuli, known as sense neurons, are located in the posterior of the spinal medula, in the region which faces the back, while the neurons which control the muscles (motor neurons) are located in the part of the medula which faces the stomach. These neurons control the reactions which originate with skin contact or or with visceral stimuli.

Now the group of reflex responses we are born with are not sufficient for our adaptation. If we relied only on those reflexes, it would be difficult for us to survive. Suffice it to say that reflex responses form part of a group of reactions called consumatory responses, that is, responses which help us avoid continual damage to our bodies, or to receive and assimilate stimuli which enhance our abilities of self preservation.

For the organism to survive, it learns anticipatory behaviors. Presented with hunger, the body does not wait for food to present itself; it initiates a search. Presented with a stimulus which might cause pain, the body initiates evasive behaviors.

Direct connections, well-established at birth, between sense neurons and motor neurons, allow only pre-established responses. For another kind of response to appear, the establishment of a distinct type of connection is required. Certain sense neurons must associate themselves with motor neurons with which they have had no previous contact. How does this happen ? Learning is explained precisely as a result of mediating mechanisms which establish new connections in the brain. Associative neurons are the workhorses of this process. In the rest of this article, we will try to explain how anticipatory responses, or series of responses not previously encountered in the genetic endownment, are aquired by means of the work done by associative neurons.