1. BRAIN: STRUCTURE AND FUNCTION
2. HEMISPHERIC DOMINANCE AND LATERALIZATION
3. LANGUAGE AREAS AND  FUNCTIONING
4. BRAIN MATURATION AND CRITICAL AGE FOR LEARNING LANGUAGE
5. LANGUAGE DISORDERS
6. METHODS OF INVESTIGATING BRAIN AND LANGUAGE FUNCTIONS
 

1. BRAIN: STRUCTURE AND FUNCTION 
If you are left-handed, you have probably felt discriminated against at one time or another: most school desks are built to be written on by right-handers,   scissors work much better if you are right-handed, and in some cultures you are not permitted to eat or even touch food with your left hand. The Devil, too, is said to be left-handed, and many words such as 'sinister' and 'gauche' come from words meaning 'left'. 'Dexterity'  comes from the Latin word for 'right'. Being 'right' in the moral sense of the word also derives from the  use of  the right hand.

As if all this were not enough, it seems that Nature, too,  discriminates against left-handers, for they  are more likely to suffer from a variety of language disorders and learning disabilities, ranging from higher incidences of  stammering to a complete loss of  language. They  seem to die younger, too. (Perhaps they get more involved in automobile or industrial accidents due to errors in the operation of equipment, equipment which is designed for right-handers.) Consequently, while almost 13% of the population worldwide is naturally left-handed, with a higher percentage among males (about 10% male and about 4% female), by age 80,  only 1% of left-handers in the total population are still alive. Why the rate of left-handedness should be so much higher for males is not known although one factor might be related to the effect of sexual hormones in the brain development of the fetus.

Left-handers need not throw up their hands in despair, however,  because among them  there is  a greater  proportion of  artists, musicians and writers than is found among right-handers.  And if you use both hands equally well,i.e., are ambidextrous,  you can take heart,  for you are in the company of the likes of Leonardo da Vinci. You might not like the word 'ambidextrous', though, since it means, from Latin, 'to have two right hands'!

Handedness is directly related to the structure and development of the brain. The brain and the spinal cord, together, make up  the central nervous system.  From the top of the spine upwards are the  medulla oblongata, the pons Varolii, the cerebellum and the cerebral cortex  (cerebrum) in that order. These  four major parts of the brain form an integrated whole by means of connective tissue. The first three are concerned with essentially physical functions, including breathing, heartbeat, transmission and  coordination of movement, involuntary reflexes, digestion, emotional arousal, etc. In comparing the brains of lower vertebrates with those of higher vertebrates and primates, such as man and the apes, the most noticeable difference is in the part of the brain which developed last in the course of evolution, the cerebral cortex.   While in fish, for example, the cerebral cortex  is barely visible and is one of the smallest parts of the brain, in humans it has increased in size and complexity to become the largest part of the brain. The cerebral cortex, itself, is a  layer of grooved, wrinkled and winding  tissue. In time, due to growth in the number and complexity of brain cells, the cerebral cortex takes on a pink-gray appearance, giving us the common term "gray matter" for referring to this part of the brain or our intelligence.

The cerebral cortex is  characterized by its division  into two halves, termed hemispheres  which are connected by tissue called the corpus callosum. The corpus callosum, it should be noted, is not only a connector for the hemispheres, but it is the principle integrator of the mental processes which are carried out in the two hemispheres.  The general appearance of the cerebral hemispheres as a whole is that of a walnut with the two adjoined parts mirror images of one another. Each cerebral hemisphere is divided into four sections: the frontal, parietal, temporal and occipital lobes. They are a convenient dividing of the brain into parts, loosely based on physical features. Functions such as cognition (to some degree) occur in the frontal lobe, general sensing (in the arms, legs, face, etc.) in the parietal lobe, hearing in the temporal lobe and vision in the occipital lobe. As we shall see later, some of these areas are also involved in the structure and function of language.

As far as our  linguistic abilities are concerned, however, it is not evident exactly how important the actual size and weight of the brain are.  Whales and elephants have bigger brains, but they also have bigger bodies, so it might be the ratio of brain to body size and weight which is important. However, the brain of the average 13 year old human weighs 1.35 kg and the proportion to body weight (45 kg) is 1:34. This is the same ratio as in a 3-year old chimp. Thus, while brain size is almost certainly related to general intelligence in a very broad sense as one moves up the evolutionary ladder from species to species, there is no indication that size and size alone is the crucial factor which would explain human language  and non-human lack of language. Structural differences must exist which account for intelligence, language and other highly cognitive functioning.
back to top

2. HEMISPHERIC DOMINANCE AND LATERALIZATION 

The brain controls the body by a division of labor, so to speak. The left hemisphere controls the right side of the body, including the right hand, the right arm and the right side of the face, while the right hemisphere controls the opposite side of the body. Those who have suffered a stroke  (cerebral hemorrhage) provide clear examples of how this kind of cross-over control operates. A stroke in the right hemisphere of the brain will  leave victims affected on the left side of the body. Thus, they can lose control over the muscles in the left hand, left leg and the left right side of the face (including that side of the tongue and mouth),  with the result that their ability to move the left arm and leg and to speak clearly will be affected.

However, a stroke would not affect vision and hearing in exactly the same way. A stroke in the relevant areas in one side of the brain would not automatically render useless the eye and ear on the opposite side of the body, since there is a crisscross control when it comes to our organs of sight and hearing. For sight, there is what is termed ‘fields of vision,’ in which connections from each eye is separated in two, sending the left half (left field) of what it sees to one hemisphere and the right half (right field) to the other. The two left and right fields are then integrated as a whole in the brain. Hearing  works in a somewhat similar fashion with fibers of the acoustic nerve in each ear distributing the incoming signal to both hemispheres. However,  more fibers from the left ear crossover and  connect directly to the right hemisphere than the number of fibers connected directly to the left hemisphere.  Conversely, more fibers from the right ear cross to the left hemisphere than the number of fibers connected to the right hemisphere.

Now, even though the hemispheres of the brain divide the labors of the body, they do not do so evenly. In a sense, we might say that the body cannot serve two masters; one side must take charge. To have the two hemispheres  competing over  which hand should be used first to fight off an attacker or to hunt with would not be advantageous to the survival of the species. This phenomenon where one hemisphere  is the major or controlling  one is called dominance.

For right-handed persons, the left hemisphere generally dominates the right, with the result that they tend to prefer their right hand.  Counter to expectations, only about 40% of left-handers  have right-brain dominance. The majority has left-brain dominance but their  dominance is much less marked than in naturally right handed persons. This  lack of strong dominance for left-handers  is believed to be a factor   contributing  to speaking problems and to various forms of reading and writing dysfunctions, such as  reversals of letters and words when reading and writing. However, forcing naturally left-handers to be right-handers will not remedy such problems but only serve to worsen them and create others.

Also, some studies suggest that there are differences between the brains of males and females.  In one experiment, Marion Diamond at the University of California at Berkeley, has shown that injecting sex hormones into young rats can affect the development of the thickness and size of the hemispheres of their brains. While females normally have thicker left hemispheres (one specialization of which is general sensory functions) and males have a thicker right hemisphere (one specialization of which is visual-spacial functions), her injection of hormones had brought about a reversal of hemisphere thickness in the sexes by the time the rats became young adults. Diamond believes that the same hormone-affecting-brain situation could occur in humans, too.

 The brain assigns, as it were, certain structures and functions to certain hemispheres of the brain. Language, logical and analytical operations, and higher mathematics, for example,   generally occur in the left hemisphere of the brain, while the right  hemisphere is superior at recognizing emotions, recognizing faces and taking in the structures of things globally without analysis. This separation of structure and function in the hemispheres is technically referred to as 'lateralization'. Incoming experiences are received by the left or right hemisphere depending on the nature of those experiences, be they speech, faces or  sensations of touch.

Associated with  lateralization is what might be termed ‘earedness,’ where persons with lateralization for language in the left hemisphere will perceive more readily speech  sounds through the right ear than the left. When speech sounds are presented simultaneously to both ears  (dichotic) in  listening experiments, those to the right ear are preferred. For example, a person with normal hearing in both ears who is simultaneously presented with "ba" through an earphone on the left ear and "da" through an earphone on the right ear,  will perceive "da" more strongly or dominantly. This is probably because “da”  passes directly to the language processing centers in the left hemisphere while the “ba” speech sound coming in the left ear must  travel a longer route; the “ba” will automatically go to the right hemisphere first, but then be rerouted to the language areas in the left hemisphere through  the corpus callosum connection.  Because of the longer path the speech sound presented to the left ear must travel, that sound would arrive at the language center after that of the sound presented to the right ear. (As we noted above, incoming sound mainly crosses over to the  opposite hemisphere.) Arriving later may well be what weakens its effect. This situation does not hold for all types of sound, however. Music and non-linguistic sounds, noises and animals sounds, for example, are perceived more strongly in the left ear, since they are processed in the  right (non-language) hemisphere.

For our purposes, we are concerned with the lateralization of language, that is, the hemisphere and areas of the brain  which are involved in the use of language.   Research has clearly shown that language centers predominate in the left hemisphere in right-handed people and sometimes in the right hemisphere for left-handed people. The main language centers  in the left hemispheres are Broca's Area, in the front part of the brain, Wernicke's Area, towards the back, and  the Angular Gyrus, which is even further back.  Broca's Area and Wernicke's Area are connected by  tissue  (the Arcuate Fasciculus). It is worth noting that these areas are not  found in the right hemisphere.

While the two hemispheres superficially appear to be identical mirror images of one another, research has demonstrated that this is not the case, neither structurally nor functionally.  Wada has shown that infants at birth have a bulge in the left hemisphere, where language is typically located, but not in the corresponding area of the right hemisphere. Also, in a group of 100 normal humans, Geschwind and Levitsky have demonstrated that  Wernicke's Area is generally larger than the corresponding area in the right hemisphere. Moreover,  such asymmetry of the brain is even present in the fetus, appearing by the 31st week.

Certain aspects of lateralization have  been dramatically confirmed by the work of Sperry, who   separated the hemispheres of the brain by severing  the connecting tissue, the corpus callosum, of a number of patients. (The purpose of the procedure was to treat  extreme cases of epilepsy.)  With the corpus callosum no longer intact,  information no longer flowed from hemisphere to hemisphere as it does in normal persons with intact brains. The functions of the complete brain were no longer integrated. By experimentally allowing information to reach only one hemisphere or the other, e.g., showing written words to the right visual field only,  researchers were thus able to test the abilities of the separate hemispheres. It was found that ‘split-brain’ persons still could use speech and writing  in the disconnected left hemisphere but that their  right hemisphere had little such capacity. In normal person, the right hemisphere has more capability.

When tactile (touch) information passed to the left  hemisphere, split-brain patients were  completely capable  of verbally describing objects and talking about things they had just touched for example. If however, patients experienced things only with the right hemisphere they could not  talk about the experience at all, since the information could not be passed through the severed corpus callosum to the left hemisphere for expression  in speech. The right hemisphere, in general, was also incapable of imagining the sound of a word, even a familiar one, and patients failed simple rhyming tests, such as determining by reading, which word, 'pie' or 'key', rhymes with 'bee', while the right hemisphere was better at spatial tasks such as matching things from their appearance, e.g. being able to correctly reassemble halves of photographs. Generally,  these tests showed  only that the left hemisphere has the capability for speaking or writing. back to top

3. LANGUAGE AREAS AND FUNCTIONING
The model most researchers  use today in describing how we understand language is still one largely based on that proposed by Wernicke over a century ago. Wernicke observed that  Broca's Area was near that part of the brain which involves  the muscles which control speech while the area which he identified, later called Wernicke's Area, was near the part of the brain which receives auditory stimuli. Based on these observations, Wernicke hypothesized that the two areas must in some way be connected.  (Later research showed that they are, indeed, connected by  the arcuate fasciculus.) Thus, according to Wernicke, in hearing a word,  the sound of the word goes from the ear  to the auditory area of the temporal lobe and then to  Wernicke's Area. If a heard word is then to be repeated aloud, the sound must  pass  to Broca's Area (by way of the arcuate fasciculus). Here, a program for the vocalization of speech is activated.

 Broca's Area is adjacent to the region of the motor cortex which controls the movement of the muscles of the tongue, the lips, the jaw, the soft palate and the vocal chords. When   a word is read, according to Wernicke,  the information goes from the eyes to the visual area of the cortex, and then to the Angular Gyrus which causes the auditory form of the word to be activated in Wernicke's Area. Recent research in brain scan imaging, however, shows that the latter part of the reading process, where Wernicke's area is said to be activated, does not  occur in many instances, thereby indicating that the auditory aspect of the theory is in radical need of modification. (A more detailed discussion of this particular problem is presented later in this chapter.)

Although most language processes occur in  Broca's Area, Wernicke's Area and the Angular Gyrus,  some language functioning does occur elsewhere in the left hemisphere, and may even occur in the other, "non-language" hemisphere. The ability to attach and understand intonation, such as the rising tone of a question,  the ability to interpret emotional intentions,  such as anger or sarcasm from  inflections in the voice,  and the ability to appreciate  social meanings from something such as whispering, may very well be located outside of what have  been  traditionally regarded as the main language areas of the brain.  Such secondary components of language are  not only more spread out than previously thought, but may vary  in location from person to person. back to top

4. BRAIN MATURATION & CRITICAL AGE FOR LEARNING 
   LANGUAGE

Much speculation has been devoted to whether there is a critical age in first language learning and in second language learning. By ‘critical age’ is meant here an age beyond which language learning will be difficult or even impossible.

There is  evidence that damage to language areas in the left hemispheres of very young children are compensated for, with the right hemisphere taking over the reacquisition of language functions. Language then become located in the right hemisphere for these individuals.

Lennenberg, who based on his work with aphasiac children, set puberty as the age or time in a child's life beyond which this kind of recovery would no longer occur. Other researchers such as Krashen have since found that the age limit of recovery is much lower,  approximately at age 5 years. Some theorists   have interpreted  studies such as these as indicating that there is an age beyond which normal children would no longer be able to learn a first or second language.  According to them, a child who had been entirely deprived of language until after the ‘critical age’  had passed, would no longer be able to learn language, or only learn a little with great difficulty. However, it is our view that studying the recovery of lateralization in brain-damaged children is an insufficient basis for  concluding that there might be a critical age for first language learning in normal children.  It is not known how an undamaged  left hemisphere, normal in every other respect except for never having been exposed to language, would react when it is exposed to language for the first time. As a result, the age limit of potential language learning in an undamaged left hemispehere might well be beyond the five-year limit proposed by Krashen on the basis of damaged brains. As we saw with children raised in the wild or in deprivation, the precise condition of their brain prior to being normally exposed to language could not be determined.

With regard to a critical age for second language learning, five years could not   be a critical age because  evidence undeniably shows that children learn a second language with ease until about 10 years of age. Perhaps, all we can say for sure is that children are generally better than adults at acquiring native speaker pronunciation in a second language (see Chapter 8 for further discussion). Since pronunciation is a motor skill where speech articulators such as the vocal chords, tongue, and mouth are controlled by muscles, an adult's difficulty in acquiring native speaker pronunciation in a second language is probably part of the overall decline in motor skills which occurs around puberty. Clearly, you will make a better gymnast or pianist if you start at age 7 than if you start at 27. Undoubtedly, the  decline in motor skills is  related to the development of the brain; but just what that development might be has yet to be determined. Similarly, the decline in rote memory ability (simple  associations) which declines with age  is also somehow related to the development of the brain.  Since other aspects of second language learning do not decline with age,  it appears that only motor skills and rote memory  decline as the result of brain maturation. The learning of grammar may be unaffected.
back to top

5. LANGUAGE DISORDERS
Language disorders known as aphasias are presumed to have as their cause some form of damage to  some specific site in the hemisphere where language is located.  Such damage causes characteristic problems in spontaneous speech, as well as in  the understanding of speech and writing. A study using radioisotope scanning in 1967 by Benson served to support the traditional distinction that aphasias are generally classifiable into two groups, Broca's aphasia and Wernicke's aphasia,  in finding abnormalities in those two areas. (In most persons, Broca’s Area is located in the  frontal lobe of the left hemisphere and, in most persons, Wernicke’s Area is in the temporal lobe of the left hemisphere.) In addition to these two basic groups, other dysfunctions were also found.

Broca's Aphasia

 The traditional view of Broca's Area is that it coordinates speech movements. It was in 1861 that the Frenchman, Paul Broca, published the first in a series of studies on language and brain. This was the beginning of the true scientific study of cases of aphasia, a  term which describes a very broad range of language disorders which is commonly caused by tissue damage or destruction in the brain. Car accidents, war injuries and strokes are  frequent causes of such injuries. Broca  was one of the first researchers discover that damage to certain portions of the brain but not to others will result in speech disorders. The portion of the brain which he identified as involving the coordination of speech movements continues to bear his name.

One particular condition, now called ‘Broca's Aphasia,’ is characterized by meaningful but shortened speech and also occurs in writing. Grammatical inflections are often lacking, such as the third person present tense "-s" ('Mary want candy' for 'Mary wants candy')  and the auxiliary 'be' ('Joe coming ' for 'Joe is coming')  are often lacking, as are articles, prepositions and other so-called function words. In a way, the speech is similar to that of children at the "telegraphic" stage of speech production. (see Chapter 2)
Although the feature of Broca's Aphasia most noted is the fragmentary nature of  speech production,  it has only been recently discovered that speech comprehension  is affected, as well. In one experiment, a patient with Broca's  Aphasia, when presented with the sentence,  "The apple that the boy is eating is red,"  could understand the sentence, particularly with regard to who is doing the eating (the boy is doing the eating). However, when presented with the sentence,  "The girl that the boy is looking at is tall," the same patient could not figure out who was doing the looking (the boy is looking at the girl).  In the first sentence, one can guess the meaning from knowing the vocabulary items 'apple,'  'boy'  and 'eat,'  and from knowing what usually happens in the world (boys eat apples and not vice versa).  But you cannot guess the meaning of the second sentence simply from the vocabulary, because boys look at girls and girls look at boys.  To understand such a sentence, one must be able to analyze its syntactic relations. Thus, there is a loss of syntactic knowledge in both speech production and understanding for those with Broca's Aphasia.  Interestingly, people with Broca's Aphasia can often sing very well,  even using  the same words and structures which they are unable to utter in  conversation. This shows that Broca's Aphasia is not simply a breakdown in the muscular control of speech movements, since those with this  disorder can  pronounce words to some extent  The loss, therefore, must extend to  something  of a deeper  nature, probably involving intention and control.
 

Wernicke's Aphasia

 This condition is characterized by speech which often resembles what is called nonsense speech or double-talk.It sounds right and is grammatical, but it is meaningless. It can seem so normal that the listener  thinks that he or she has, as is often the case in ordinary conversation, somehow misheard what was said  and therefore did not understand it. A patient with Wernicke's Aphasia may say, "Before I was in the one here, I was over in the other one. My sister had the department in the other one,"   "My wires don't hire right." or "I'm supposed to take everything from the top so that we do four flashes of four volumes before we get down low."

 Patients with Wernicke's Aphasia also commonly provide substitute words for the proper ones on the basis of similar sounds, associations or other features. The  word 'chair,'  for example,  elicited the following in some patients: "shair"  (similar sound),  "table" (association),  "throne" (related meaning),  "wheelbase" (uncategorizable)  and "You sit on it. It's a…" (word loss).  As with Broca's Aphasia, Wernicke's Aphasia can also cause a severe loss of speech  understanding, although the hearing of nonverbal sounds and music may be unimpaired. For example, a person might be able to hear songs quite clearly and even sing one which he or she has just heard but yet be unable to recognize the lyrics of the song as words.

Other Aphasias

In addition to the kinds of aphasias which can occur from damage to the two main language centers of the brain, Broca's area and Wernicke's area, there are other aphasias which occur from damage at sites near or  between those areas, and at other sites in the brain yet to be determined.   Damage to the area which leads into  Wernicke's area from the auditory cortex results in  pure word deafness, where one cannot recognize the sounds  of words as speech but can hear other types of sounds. For example, a person might be able to hear music quite clearly and even  sing a melody which he or she has just heard, but be unable to recognize the lyrics of  that  song as words.

A condition known as conduction aphasia  is characterized by poor repetition of speech words despite relatively good  comprehension.  Persons with this aphasia might substitute a closely related sound for the one they actually hear, e.g., for "teethe" they say "teeth," and for "bubble," they say "bupple" (here inventing a new word, but one that fits the way sounds are combined to make English words.) Some may also have the ability to repeat number strings of 4 or 5  digits, e.g. 4592, 38427, yet be unable to repeat a simple three syllable sentence accurately, e.g., “Joe is here,”  “Betty sang.”

Anomic aphasia  involves problems  in finding the proper words for spontaneous speech, even though language comprehension and repetition are good. Typically, such a person has difficulty finding the correct names for objects. This is a phenomenon which we all experience on a much reduced non-pathological level at one time or another, e.g., "Hand me…that…uh…uh…uh…thing …over there."

There are also reported cases of patients being unable, in response to a verbal command, to perform skilled motor movements with their hands, even though they understand the command and their spontaneous hand movements are perfectly normal. Thus, while a person might spontaneously  be able to pick up a pen, he or she may not be able to perform the same task when asked to do so. This inability to respond appropriately to verbal commands is called 'apraxia'.

There is also global aphasia, a terrible condition in which many or all aspects of language are severely affected, presumably due to massive damage at numerous sites in the left hemisphere or to critical connections between language areas.  Such   patients demonstrate little speech comprehension and  display, at best, some stereotypic and automatic sequences of speech sounds. One  woman  who had suffered a massive stroke could say nothing but  four nonsense syllables, "ga dak la doh," every time she tried to speak.

In trying to determine what kind of aphasia will be produced by what kind of damage, there are a number of variables which must be taken into consideration.  For example,  it is not just the location of damage to the brain which matters, it is also important to know  what the nature of the damage or the lesion is. Was tissue completely destroyed or was the damage slight?  Did the damage  occur suddenly or slowly over time?  Since childhood lesions may leave a mild deficit that can be difficult to detect, and since the same lesions in an adult would be much more noticeable, it is necessary to know at what age the damage occurred.
The type of aphasia which involves disorders in reading and writing is called 'dyslexia'.

There are many sorts of dyslexia, one category of which is due to damage to the brain after reading and writing have been acquired. With children, dyslexias may be observed in the process of their acquiring reading and writing skills. Problems of hemispheric dominance, defects in visual perception or even the effect of using a poor teaching method have all been claimed to play a role in causing some children to read or write backwards (deer  is read as reed ), to reverse letters (b  and d ),  confuse their orientation (u  and n ) and a variety of other anomalies.

Dyslexia may be subdivided into two basic categories: alexia  or disorders in reading, and agraphia  or disorders in writing. One may  be afflicted by both conditions at the same time, in which case a person is  unable to either read or write. In 'pure agraphia' there is a total loss of the ability to write, although the hand can be used skillfully for other purposes. Thus, for example, a person who has had a left hemisphere stroke or damage due to other causes may be able to read the simple sentence 'How are you?,' and yet be  unable to write it when it is dictated verbally. Also, some may be unable to read a phrase, yet be quite able to write it as dictation. That condition is termed alexia without agraphia.  (They will even be unable to read what  they themselves have just written!) It is, in a way, the written equivalent to certain aphasias mentioned earlier, where a  person may be able to say they want. Yet when their speech is auditorily recorded and the tape is played back to them, they are unable to understand what they  have just said.

Even more unusual conditions can occur. For example, some alexics may be unable to read words but be able to read numerals. There are also conditions caused by damage to the connective tissue (the corpus callosum) between the hemispheres; these can  produce conditions in which, for example, a person may be able to write correctly with one hand,  but produce meaningless but legible written language with the other hand. (Ordinary persons generally manage to write legibly with their other hand, as uncomfortable as it may be.)

Studies involving languages with unusual writing systems have produced interesting results. Japanese aphasics display unusual characteristics due to the nature of their writing system, which   has both a syllabic system (in which symbols represent syllables) and   Chinese type characters (in which symbols represent meanings)   Imura at the Nihon University College of Medicine studied a patient with Broca's aphasia who was able to a write the correct  character for a dictated word, but was unable to write the same words in the syllabic system, something that any normal Japanese can do.  Then there was a patient with Wernicke's aphasia who was able to write characters quite fluently, but, as is the case with much of the speech of those with Wernicke's aphasia,   what was written was nonsensical:  the characters were malformed or made up of invented sets of strokes.

 Besides writing problems, reading by Japanese can also be affected in strange ways in terms of the syllabic (kana) and character (kanji) systems. The noted researcher Sasanuma has found that while some  patients may have their reading of kana words (familiar ones) impaired, their reading of kanji words (familiar ones) may not be much impaired,  or vice-versa.  These are right-handers who have had damage, due to  strokes (cerebral hemorrhages), automobile accidents, in the temporal or parietal regions of their left hemisphere.  In some cases, the loss is undoubtedly due to damage of storage areas in the brain for kana and kanji words. However,  as Sasanuma points out, there may be damage to some processing or retrieval areas in the brain that yields these results and other strange outcomes, as well. Incidentally, it might be worth pointing out a common fallacy concerning Chinese characters and kanji. These are not located in the right hemisphere (in ordinary right-handed persons), although these symbols are historically derived from pictures. They are located in the left hemisphere as are all writing systems.
back to top
back to page on Language Disorders

6. METHODS OF INVESTIGATING BRAIN AND LANGUAGE FUNCTIONS 
The comparatively little  understanding we have  of the neurological basis of language in the brain is the result of the application of a relatively small number of methods. The oldest method, that used by Broca himself, is the postmortem examination of the brains of patients who had displayed language disorders while they were alive. The  abnormalities he found in certain areas in postmortems of their brains correlated with the language symptoms they displayed while alive.  Another method involves  observing  the language of patients who have had brain operations. A person might require, because of an accident or a tumor, for example, the removal of a lobe of the brain (lobectomy)  or even of an entire hemisphere (hemispherectomy).  Then, too, the  study of the language of patients with severe brain damage  caused by accidents or wartime injuries was and  still is a common method of investigation.

Another method for trying to determine which part of the brain has to do with particular aspects of memory and language involves the electrical stimulation of the cerebral cortex in patients who are conscious during brain surgery. Patients would say they remember childhood events or even old songs on stimulation.  Penfield pioneered this procedure but its results, aside from being controversial (how to verify what the patient said was remembered was one problem), has been very limited since it is restricted to open brain areas of persons who were undergoing surgery while not being anesthetized.

 But, it is just in recent years, that revolutionary new methods of studying the brain and language have been developed. These have been made possible through powerful new techniques in radiological imaging. CT or CAT (Computerized Axial Tomography) and PET (Positron Emission Tomography) are the most widely used in this regard.  A CAT scan involves using an X-Ray source so as to make numerous thin slice scans the images of which are integrated by computer to construct an image of a  whole brain or portion of it.  Both of these techniques use the brain as it is, without surgery or any other radical procedure. As such they may be used with normal persons as well those with brain problems.

 Curious scientists recently used CT to examine a section of the brain of Broca's original patient, Leborgne,  who is better known in scientific literature as "Tau". (He was nicknamed this because that sound was the only one that he could utter.) The brain has been preserved for over a 100 years in a medical museum in Paris!  Modern  researchers were able to reexamine, as it were, the patient, to determine  just which areas of the brain had been affected.  Tomography has shown that  Broca was essentially correct in concluding that the language deficits of the patient had indeed involved trauma to the area of the brain which  bears his name.

CT has shed light on intermediate aphasias caused by damage along the pathway in the brain  between Broca's and Wernicke's Areas. This has been termed conduction aphasia. Because they generally do not involve the two major language areas in the brain, these aphasias feature language which is remarkably normal in understanding and spontaneous production but marked by poor passage of auditory information to Broca's area and into the motor system. This impairs the patient's ability, for example, to repeat sentences spoken to them.

The  newest (the 1980’s) and most exciting  technique to be developed is that of Positron Emission Tomography, the PET scan. Unlike CT, which images slices of the brain and integrates them into a whole, PET allows for the  direct observation of the brain as a whole.  Like CT, however, it allows for the study of language in both the normal or damaged brain. The PET procedure involves injecting a mildly radioactive substance into the blood and then tracing the blood flow patterns within the brain by means of an imaging technique.  With PET,  areas of the brain  "light up"  in different colors when there is an increase in blood flow (an indication of increased brain activity)  and this can be seen  by special equipment.  As subjects perform various linguistic tasks given to them by researchers, it becomes possible to map the areas which underlie language use in the  brain in a  way that was never possible before.

In reading, for example, the PET scan shows that light signals from the eyes (as we look at the printed word) are sent to the visual area of the cortex ( in the occipital lobe) then forward to the visual association areas.  When  speech is heard, on the other hand, the acoustic signals from the ear go to the auditory cortex (in the temporal lobe). PET scans are able to determine how closely   models of speech production and understanding, and of reading and writing  conform to reality.

PET has already provided evidence that counters one view reading which holds that the printed word must always be sounded out in order to be understood. It showed that visual forms of words  may  be sent directly  to the  semantic areas in the frontal lobe for comprehension. Access to the stored auditory form in the angular gyrus for mentally sounding out words is not necessary in the recovery of meaning. This direct semantic connection occurs mainly  with common, familiar words. However, even when people have learned to read by a method of sounding out letters, like  Phonics, after a number of exposures to the written words, the sounding out activity will be bypassed and the semantic areas will be directly activated. Only when a special task is presented, such as trying to figure out which word,’blue’ or ‘go,’ rhymes with shoe,’ (the words are presented in written form), then a portion of the brain near the auditory cortex "lights up" indicating that internal sounding out is going on.
PET studies have also challenged the traditional view,  held as late as 1980, that Broca's Area was used only for speech production.   PET has confirmed that Broca's Area  is involved  not only with the movements related to speech, such as moving the vocal chords, tongue and  lips but even when the hand is moved.  Not only that but the area lights up  when the person is just thinking about  moving the hand! Broca's area is now viewed as a general motor programming area. back to top

Localism  and Holism

Much of the discussion  in this chapter has been aimed at showing in a very broad way how the production and understanding of language is related to certain areas of the brain and their interconnections. This particular model of looking at the structure and function of language  by relating specific aspects of language to certain localized areas of the brain is called  the localist  model. Certain techniques we have mentioned in studying the brain, such as electrical stimulation, PET scans, etc. lend themselves particularly well to exploring the functions of localized areas and have been quite successful in this respect.

 Although it is scientifically sound  to accept the view that certain areas of the brain are involved in language, it is also necessary to take into account holistic or global phenomena which involve  broader psychological factors, such as attention span, motivation, the rate at which auditory and visual memory traces dissipate, alertness, etc. A holistic  type of model does just this. As examples of holistic phenomena  consider the following. You start to say something and suddenly you are distracted and break off or you forget what you wanted to say.  It would not be a justifiable conclusion that you have suffered a  momentary breakdown in speech production due to some damage to your Broca's Area.  Or, when a friend says something quite audibly but you do not catch the words and  you respond with a "What?", is your Wernicke's Area breaking down? Of course not. Some sort of holistic multi-dimensional explanation is required here.

Also, very importantly, there are cases of aphasia which have been examined clinically that do not correspond to the localist model. Some patients with aphasia have turned out to have  areas of their brains affected or unaffected in ways that do not correspond to the view that a certain behavioral dysfunction must always be the result of damage to one particular area of the brain. The localist model has been successful in explaining roughly 85% of aphasias, but the other 15% are anomalous and baffling. They represent people who have language disorders but do not have damage in the expected language areas, or, conversely, certain damage has not resulted in the predicted symptoms. This cannot but make us reflect on the more global aspects of language in the brain.

Furthermore, it is possible that, as some studies now suggest, the failure to produce grammatical sentences in some aphasias may not be  a loss of actual knowledge, but rather a breakdown in the process of constructing sentences; that is, aphasics still ‘know’ grammar, but they no longer know how to use it.

There is, indeed,  an impressive accumulation of scientific knowledge on the brain to date.  Given the fact that even such linguistic concepts as simple as that of the noun or a verb has yet to be localized in the brain, it is clear we are a long way from establishing the detailed knowledge of the direct correspondence between language and the structure and function of the brain that we would like to have.  back to top