RIGHT BRAIN - LEFT BRAIN & THE CONSCIOUS & UNCONSCIOUS MIND
THE LEFT HEMISPHERE
LANGUAGE & CONSCIOUSNESS
Language is often a tool of consciousness. We usually think in words and use language to label, describe, and communicate our experiences. It is through language and thought that we are able to manipulate the world, describe our selves, make predictions about the future, and symbolize aspects of the past in verbal memory and in written form. Via these modalities we are able to analyze and describe the world as we view it and express our selves in a multi-modal, multi-dimensional fashion.
Consciousness, language, and linguistic thought are not only intimately interrelated, but all are supported and maintained by the left half of the brain. It is the left brain which controls the ability to talk and think in words and it is the left brain which listens and analyzes spoken and written language. The ability to produce linguistic knowledge and thought, to engage in mathematical and analytical reasoning, or to process and express information in a temporal-sequential, grammatical, and rhythmical fashion, are associated with the functional integrity of the left half of the brain in most of the population. It is the left brain which we associate with linguistic consciousness.
In contrast, the right half of the brain cannot read, spell or write, and cannot understand many aspects of human speech except a few simple words, particularly those which are emotional. However, it can still vocally express itself through singing, swearing, crying, praying, mimicking, or cooing sounds of love and sorrow. The right hemisphere cannot talk. It is the left half of the brain which does all the talking.
In fact, there is one area within the left brain which controls the ability to speak whereas there is yet another region that mediates the ability to understand speech. These regions are referred to as Broca's expressive speech area, located in the left frontal side of the brain, and Wernicke's receptive language area which is found along the left temporal side of the brain, beneath the area where the ear is located 1-2.
LANGUAGE & THE LEFT HEMISPHERE
If a person were to suffer a left brain stroke such that Broca's area were injured, word finding and the ability to speak would be greatly curtailed. This condition has been referred to as an expressive aphasia. It has also been called Broca's aphasia (named after the Dr. Paul Broca who first localized and described this symptom in detail). Interestingly, although unable to talk, many patients are still able to sing, curse, and even pray 3-5. Such patients may have little problem understanding the speech of others.
If a patient suffered an injury to the left temporal area of the brain such that Wernicke's receptive language area was damaged, the ability to understand and comprehend human speech or written language would be greatly diminished. This is because the left half of the brain and Wernicke's receptive speech area are highly involved in discerning temporal sequences including the units of speech. That is, Wernicke's area acts to organize and separate incoming sounds into a temporal and interrelated series so as to extract linguistic meaning via the perception of the resulting sequences.
Hence, when this area of the brain is damaged a spoken sentence such as the "big black dog" might be perceived as "the klabgigdod," or as "thbelickblacdokdg." However, comprehension is improved when the spoken words are separated by long intervals.
The loss of verbal comprehension is referred to as receptive aphasia. This condition has also been called Wernicke's aphasia (named after Dr. Carl Wernicke who first localized and described this condition in detail). These patients can still talk, however. Unfortunately a lot of what they say sounds like nonsense.
THE LANGUAGE AXIS & THE TRAIN OF THOUGHT
Wernicke's area and adjacent brain tissue not only decode and organize incoming speech sounds, these regions also act to organize sequentially and to impose temporal sequential order on everything a person is planning to say as well. When a person wishes to talk, this information and code is then transmitted from Wernicke's to Broca's area so that it can be expressed. Because of this relationship patients with receptive (Wernicke's) aphasia often speak nonsense as the temporal sequential and grammatical order and arrangement of their outgoing speech has become abnormal. Sentences such as the "big black dog" might come out as "belick blacdok".
Wernicke's area is linked to Broca's area by a rope of nerve fibers called the arcuate fasciculus which allows information to be transferred between these regions. This rope of fibers also makes contact with an area of the brain called the angular gyrus located in the parietal lobe. These three areas form a highly interactional linguistic unit.
THE ASSIMILATION OF MULTIPLE IDEAS AND ASSOCIATIONS
The angular gyrus is uniquely situated such that the areas of the brain which process visual, tactual, and auditory information are at its borders where they all intercommunicate. That is, the angular gyrus sits at the juncture where touch is processed in the parietal lobe, where visual analyses are performed in the occipital lobe, and where sounds are analyzed in the temporal lobe. It is in the angular gyrus that auditory, visual, and tactile sensations are combined to form a multi-modal representation of what is being experienced.
It is via information exchange in this border area that we are able to touch an object and are then able to visualize what it looks like and determine what it is called without even seeing it. Similarly, if we hear a sound we are also able to determine what the object might look like, how it might feel, taste, etc., as all these different associations are linked together in this area. That is, via its interconnections with various brain areas, the angular gyrus is able to call forth ideas and relevant associations and then link them together to form concepts and categories.
It is in this manner that when we read the word "Chair" we are able to visualize what it would look like, what the word sounds like, what it might feel like to sit in one, even how much one might cost. Moreover, we can think of a variety of chairs all of which may look and feel quite differently. This is accomplished via the angular gyrus which is able to call forth associations from other brain areas and then assimilates associations in a multi-modal fashion. The angular gyrus is thus crucial in the organization of language and thought and it is a structure unique to human beings 6.
Together these 3 brain regions, Broca's and Wernicke's area and the angular gyrus, along with other brain structures allow for the expression and understanding of both spoken and written language. It is in this same manner that verbal thoughts are formed.
If we wish to describe something to a friend these regions become activated such that Wernicke's area begins to organize the grammatical order of what we intend to say, whereas the angular gyrus is busy calling for associations from other brain regions so that what we say has become properly labeled; so that we do not call a "spoon" a "stirrer" or a "fork" by mistake. Lastly, this information is then transferred from the angular gyrus and Wernicke's area to Broca's area and our thoughts and ideas are expressed 7.
RIGHT HEMISPHERE MENTAL FUNCTIONING
There is enormous evidence which indicates that the right hemisphere subserves a type of awareness which is considerably more ancient as well as qualitatively different from that manifested by the left. However, this was not always the case. For many hundreds of thousands of years the human brain and original mind of our Homo sapien ancestors had increasingly become more proficient at hunting and stalking prey, exploiting the environment, and socializing as bands and tribes increased in size and complexity. With the exception of left brain dominance for handedness, both halves of the brain performed quite similar functions for many millions of years.
With the development of language and writing, these other more ancient specialties associated with the original mind probably became increasingly crowded out of the left half of the cerebrum and came to be represented only within the right hemisphere. However, the evolution and elaboration of right hemisphere functions also continued unabated.
Among modern humans it is the right half of the brain which is responsible for discerning distance, depth and movement, recognizing environmental and animal sounds, for controlling most aspects of emotion, social behavior, body language, as well as the capacity to sing, dance, chase or throw something with accuracy, and run without falling or bumping into things. The visual, emotional, hallucinatory, hypnogogic aspects of dreaming are also associated with right hemisphere mental activity 8-14.
MUSIC, MELODY & VISUAL SPACE
The right cerebral hemisphere is associated with nonverbal environmental awareness and the capacity to recognize emotional and environmental sounds such as a chirping bird, a buzzing bee, a babbling brook, or a thunderstorm 15. Related to this is the ability to sing and recognize musical melodies 16.
If select portions of the right hemisphere were damaged, that person would be unable to recognize music, but instead might hear noise. If birds were singing or if rain drops were falling, he might be unable to recognize what he was hearing. He probably would never notice the sound. Moreover, this same right hemisphere damaged patient might be unable to sing although he could still talk without much problem. He could say the words but have much difficulty singing them.
The right hemisphere is also dominant in regard to the perception of movement, speed, distance and depth as well as the geometric analysis of gestalts, angles and visual relationships 17. The right hemisphere enables us to maneuver successfully about in space without getting lost, to detect and analyze the movement of others, and to determine in what manner these actions and motions are interrelated. In this regard the right hemisphere was no doubt critically important in the survival of our ancient hunting ancestors, enabling them to detect, stalk, and dispatch various pray with alacrity and then to find their way home without the aid of street signs.
Because of these same right hemisphere capabilities we can walk, run or dance without tripping, can determine if something is near or far away, can catch or throw a ball with accuracy, and can drive a car without bumping into things along the roadway, such as cars or pedestrians while our "thoughts" are elsewhere. Likewise, if not for the proficiency of the right hemisphere, most forms of sports, gymnastic and athletic competition would be impossible.
The left half of the brain is concerned with grammatical relationships, temporal sequential organization (such as first vs last), and the analysis of details and parts. The left brain cannot see things as a whole, it never sees the "big picture," only an assembly of parts. It cannot see the forest, only a sequence of trees.
The right hemisphere can visualize and fully comprehend and perceive a complex visual array as an interrelated whole (or gestalt). Whereas the left brain might see "132" trees, the right hemisphere sees a forest. Whereas the left brain sees a nose, a mouth, an ear, and lips, the right hemisphere sees a face.
The right hemisphere can thus "read between the lines" and infer what something might be or mean, based only on a few features. It is able to determine how things and events may be interconnected and interrelated so as to deduce its overall configuration and all encompassing gestalt 18.
As a consequence of the right hemisphere's ability to "fill in the blanks" and deduce or determine what something might be or mean, even when presented with at best scanty information, it is often thought of as the more intuitive half of the cerebrum 19.
THE HUMAN FACE
Due in part to its superior capacity to perform visual closure and forms gestalts, the right half of the cerebrum also mediates the capacity to recognize faces 20. This is because the human face is not perceived as an assemblage of parts but as a whole. Indeed, if you were to focus on the parts of a friend's face rather than the face in its entirety, it would look unfamiliar.
If certain regions within the right hemisphere were damaged, faces may also begin to look unfamiliar. The patient might be unable to recognize the faces of friends or loved ones, and might be unable to recognize his own face in a mirror; a condition referred to as prosopagnosia. As a consequence of this condition some patients become paranoid and convinced that their wife or husband has been replaced by an impostor as the faces of their loved ones no longer look familiar.
The right hemisphere also enables us to analyze facial expressions and facial emotion. Hence, we are able to tell if someone is upset, angry, sexually aroused, or disbelieving by the looks given us.
If damaged, the patient could consequently lose the ability to perceive facial emotion and would never know why you might be looking at him in a certain manner. Others with less extensive damage simply misread the emotions being expressed by someone's facial gestures, grimaces and eye movements.
The left half of the brain controls the movements of the right half of the body. The right hemisphere controls the left side of the body.
Similarly, the left brain perceives visual stimuli or tactile sensations that arise from the right side. However, in contrast, the right hemisphere perceives touch and sensations that occur on both sides of the body. That is, whereas the left brain is limited to receiving information from only half of the body and surrounding environment, the right hemisphere is able to perceive sensations regardless of where they arise. In this regard, the right half of the brain is simply more sensitive and aware of the body and its environment 21.
The right hemisphere is also more sensitive to touch, pressure sensation, the ability to sense painful stimuli, and even determine how one is being touched such as in a rough versus loving manner. In consequence, the right hemisphere is more concerned with the manner in which others intimately and physically interact with us; it is the more cuddly, huggable, touchy-feely half of the brain.
THE BODY & SELF IMAGE
If something were placed in our hand, this information would be transmitted to a select region of the brain called the parietal lobe where it would then be analyzed; e.g., if it is hard, cold, short, thin, pointed, rough, wet, etc. It is in this manner that we are able to recognize what we touch and what is touching us. The parietal lobe accomplishes this as it is specialized for analyzing sensory sensation regardless of where it occurs on the body. If an insect were to land on your leg, nerve cells in the parietal lobe would become activated and you would know that something has landed and is crawling and would be able to localize the sensation as coming from your leg.
Because all sensations from the body are transmitted to the parietal lobe a sensory representation or image of the body surface is maintained by the many specialized nerve cells in this brain region. Thus all sensations from the arm go to the region of the parietal lobe which receives arm sensations and all information from the leg would go to where leg sensations are analyzed.
If we were to perform brain surgery and electrically stimulate the nerve cells in the parietal lobe where this sensory image of the body is maintained, the person would think that the corresponding part of their body was being actually touched and stimulated --when in fact it is not. That is, he may think someone was touching him on his arm when in fact it was his brain that was being stimulated. Since that part of the brain which represents a specific body part is activated the brain naturally assumes the sensation must be coming from the body.
The greater the sensory importance of a particular body part, however, the more densely will it be represented in the brain. For example, there are a large number of nerve cells which receive information from areas of the face and hand. In consequence there is a large area of the brain which corresponds to the fingers or lips as these areas of the body are very sensitive and important. By contrast very little brain tissue is devoted to the representation of the forearm as few events of sensory importance occur in this region and thus few nerve cells are needed. Thus the image of the body which is mapped out and maintained within the brain is distorted.
If a person were involved in an accident and lost an arm or a leg, the sensory body image maintained in the brain would not be affected and the amputated body part would continue to be represented in the parietal lobe. This is why some amputees continue to experience and feel as if their absent limb were still present. This is referred to as a "phantom limb" and a person may think he can feel his hand or arm even though it has been cut off long ago.
Since we have two parietal lobes, one in the right the other in the left brain sensory body images are maintained in both. In general, since the left brain receives sensation from only the right side of the body, it maintains a sensory image of only that half of the body.
In contrast, since the right hemisphere receives sensation from both sides of the body it maintains a sensory image of the entire body. In fact, the ability to imagine or visualize our body is made possible by the right hemisphere. The left brain is thus comparatively quite limited insofar as the body and self image is concerned.
DISTURBANCES OF THE BODY IMAGE: NEGLECT & DENIAL
When the parietal lobe of the right hemisphere is damaged, physical sensory functioning and the ability to perceive touch can become grossly abnormal. Although sensory information continues to be transmitted toward the brain, the brain area that is supposed to receive it may have been destroyed and the signal does not register. In consequence patients may experience peculiar disturbances which involve the body image.
If damage is quite massive, awareness of corresponding body parts would be abolished. The body image would have been erased. However, because half of the body continues to be represented in the left brain, patients continue to be conscious of half their body; but only half. Unfortunately, the left side of the body would no longer be acknowledged since the image has been destroyed 21.
In consequence, patients with right hemisphere injuries may fail to perceive stimuli applied to the left side; wash, dress, or groom only the right side of the body and ignore their left side, confuse body-positional and spatial relationships; misperceive left sided stimulation as occurring on the right; fail to realize that their extremities or other body organs are in some manner compromised; and literally deny that their left arm or leg is truly their own. They may in fact ignore all of the left half of space.
For instance, one day I was asked to examine a woman who had suffered a massive right hemisphere stroke. When I walked into her hospital room I noticed that she had brushed only the right side of her hair and had put make up on only the right side of her face. Her robe had also only been put on partially, the right arm correctly through its sleeve, the left arm and left half of her body remaining undraped. Her left arm laid limply in her lap.
After I had introduced myself and shook her right hand, I asked her to raise her left hand. She smiled at me and raised her right hand.
Dr. J: "No. That's your right hand. I want you to raise you left hand."
Patient: (again raising her right hand) "This is my hand."
Dr. J: "Yes. That is your right hand. I want you to raise your left hand. Can you raise your left hand?"
Patient: (again raising her right hand). "Yes. See?"
Dr. J: (picking up her left hand) "No. I want you to raise your left hand. Can you raise this hand?"
Patient: (looking at her left hand.) "That's not my hand."
Dr. J: (still holding her left hand). "Sure it is. This is your left hand. Can you raise it?"
Patient: (becoming upset). "That's not my hand."
Dr. J: (waving her hand in front of her face): "It's not? Whose is it then?"
Patient: "I don't know. Maybe it's yours?"
Dr. J: (showing her both his hands). No. It's not mine. I've already got two hands."
Patient: (becoming angry and irritable). "Well, it's not mine. Maybe it belongs to my husband."
Although responses such as these are seemingly quite bizarre, these patients (that is, the talking left half of their brains) are in fact telling the truth. The left hand belongs to the right hemisphere, which in their case is damaged and no longer working properly. The body image of the hand has been erased. The left (talking) half of the brain being responsible only for the right hand and now having no information about the left hand (because this information has been deleted) thus answers correctly. "That is not my hand;" that is, it is not the left brain's hand.
Why doesn't the patient remember that she has a left hand? Because those memories are stored only in the right half of the brain. The left brain has memories all its own. Hence, because the left brain also has no memory of a left hand, denying the ownership of a left hand does not seem preposterous to it. To claim a hand that you have no memory or image of would be odd.
This is yet another example of how the left brain likes to make up explanations (which it then believes), when information normally possessed by the right hemisphere is not available to it. In severe cases this is called "gap filling" and is referred to as confabulation. That is, the left half of the brain makes up explanations to fill in the gaps in the information it receives, and then it believes it's explanations 22. Since the left half of the brain often has only incomplete access to certain forms of information, impulses and desires, confabulation is an explanatory activity in which it frequently engages. Everyone confabulates at one time or another. Recall the supermarket experiment with the nylon stockings.
VOCAL MELODY, INTONATION, EMOTION, MEANING & INFERENCE
Have you ever had someone tell you: "It's not what you said. Its the way you said it."? Although you (or rather you're left brain) may have not known what this person was talking about, your right hemisphere certainly did. It is your right hemisphere which controls the way we say things. It also controls our ability to hear things said in a certain tone or manner.
Although language is usually discussed in terms of grammar and vocabulary and is associated with the conscious mental processing of the left half of the brain, there is yet another major aspect to linguistic expression and comprehension by which a speaker may convey and a listener discern intent, attitude, feeling, context, and meaning.
That is, language is both descriptive and emotional. A listener comprehends not only what is said, but how it is said --what a speaker feels. Feeling, intent, attitude and related emotional states are perceived, processed, and expressed by the mental system of right half of the cerebrum.
Feeling, be it sadness, sarcasm or empathy, often is communicated by varying the rate, amplitude, pitch, inflection, timbre, melody and stress contours of the voice. Based on studies of normal and brain-damaged subjects it is now well established that the right hemisphere is superior to the left in distinguishing, interpreting, and processing these particular vocal inflectional nuances, including intensity, cadence, emotional tone, amplitude, and intonation.
Through these abilities the right hemisphere is fully capable of determining and deducing not only what another persons feels about what he is saying, but why and in what context he is saying it --even in the absence of vocabulary and other denotative linguistic features. This occurs through the analysis of tone and melody of voice.
Hence, if I were to say to you, "Do you want to go outside?" although both hemispheres are able to determine whether a question vs. a statement has been made, it is the right hemisphere which analyzes the paralinguistic features of the voice to determine whether "going outside" will be fun or whether I am going to punch you in the nose. In so far as the left brain is concerned it would know only that it was being asked to go outside. Indeed, it is via the perception of similar melodic and prosodic qualities that our dogs and cats are sometimes able to understand what we are saying and what we are feeling.
DETERMINING CONTEXT & DRAWING INFERENCES
Even without the aid of the actual words (if they were experimentally filtered out and deleted), and based merely on vocal tone the right hemisphere can determine context and the feelings of the speaker. It can deduce if someone is being sarcastic, feeling sad, or even if he is lost and asking directions just by listening to the tone and melody of their voice. By the analysis of these same vocal features it can tell if someone is being dishonest or is attempting to mislead us. It is for these and other reasons already noted that the right half of the brain sometimes is thought to be the more intuitive and inferential half of the cerebrum.
Correspondingly when the right hemisphere is damaged, the ability to process, recall, or even recognize these melodic and inferential nuances may be greatly attenuated 23. For instance, right hemisphere damaged patients have difficulty understanding context and emotional connotation, drawing inferences, relating what is heard to its proper context, and recognizing discrepancies. Hence, they are likely to miss the point, respond to inappropriate details, and fail to appreciate fully when they are being presented with information that is incongruent or even implausible 30-33. In other words, they fail to perceive "the big picture" and can no longer tell if "things don't add up," or if someone is being dishonest. This indicates that not only does the right hemisphere subserve these functions, but that the left brain does not possess these capabilities.
These patients also tend to be overly concrete and literal. If told to read the following sentence: "He has a heavy heart," and then instructed to choose a cartoon that matched it, such as a picture of a man crying versus a man weighed down by a large red heart on his shoulders, a patient with a right hemisphere injury would pick out the picture with the heart.
If we didn't know they had brain damage, or if the injury was only quite mild (such that neither they, their family or doctor were aware of it) we might think that they are simply quite dense. In this regard, the left brain is actually quite socially-emotionally dense. In fact, many of us have met seemingly normal people who are completely devoid of the ability to "read between the lines," who fail to infer what we mean, and who just don't "get the drift" of the conversation. Such people are too literal to realize when we are kidding, being sarcastic, or when others are being deceitful or are saying things that "just don't add up." They are just not properly using their right hemisphere.
DISCERNING & CONVEYING FEELINGS
When devoid of melodic, intonational contours, language becomes like a monotone, very bland, and a listener experiences difficulty discerning attitude, context, intent, and feeling. Conditions such as these arise after damage to select areas of the right hemisphere or when the entire right half of the brain is anesthetized (e.g., during sodium amytal procedures) in preparation for possible neurosurgery.
If the right frontal part of the brain were damaged the melody of one's voice would be altered and the ability to express vocally one's feelings would be compromised. One's voice might become flat and like a monotone, or wildly distorted so that friends and loved one's might have trouble understanding what was being conveyed. With right frontal damage, the person might also lose the ability to sing and carry a tune.
James Brady, the former press secretary to President Reagan had a problem similar to this after being shot in the right frontal portion of his brain. When speaking he would sometimes lose control over his voice and he would sound as if he were crying or wailing. Fortunately, he has since recovered significantly.
If damage were to occur in the more central portion of the right hemisphere (within the temporal lobe) the person would lose the ability to hear melodic nuances, including music. As such he might misperceive what was being conveyed.
The right half of the brain is dominant for the perception and expression of most aspects of emotion. When most people smile or frown, the left half of their face (which is controlled by the right hemisphere) is more emotionally expressive. If one were to cover up half their face and look in a mirror one would also notice that there were distinct emotional differences in expression. When people speak or think in an emotional manner, their eyes will tend to dart to the left and their left arm becomes more active.
Similarly, the right half of the brain becomes more electrophysiologically activated when a person is emotionally aroused. Even sexual orgasm and the experience of body pain are more associated with right hemisphere activation.
As noted before, the right hemisphere is more adept than the left at reading emotional facial expressions, and determining mood and emotional state by the analysis of a person's voice and body language. It is even more sensitive to the emotional nuances conveyed by touch.
The right hemisphere is therefore highly involved in many aspects of emotional functioning. If injured, emotional functioning can become quite abnormal.
Though a person might become depressed with damage to the left or right hemisphere, right hemisphere damage can give rise to a wide variety of emotional disturbances. This includes mania, the loss of inhibitory restraint, impulsiveness, childishness, emotional lability or numbness, delusions of grandeur, and hysteria. Hence, the right hemisphere is dominant over almost all aspects of emotion 24.
Moreover, the right hemisphere is not only dominant in the expression and perception of emotion, it is also responsible for storing these experiences in memory. Thus whereas the left brain will store language-related memories, the right hemisphere will memorize and recall emotional experiences.
LEFT BRAIN LIMITATIONS
The right and left brains often act cooperatively. However, sometimes the left brain tries to dominate and will try to perform a task that is actually performed better by the right hemisphere 25. In some instances the left brain interferes with, suppresses and inhibits right hemisphere mental processing so that these capacities and abilities are not expressed. That is, they remain confined within the mental system of the right hemisphere and their presence is not even hinted at. This is unfortunate as two brains are better than one and it is very self limiting in that the left brain has difficulty processing and recognizing emotional signals, particularly those which are negative in nature.
Sometimes the left brain, acting in its dominant mode will so interfere with and attempt to inhibit and ignore the right hemisphere that in consequence certain emotions and feelings conveyed by others are not perceived and recognized. The person thus becomes a social dunce or has problems in relationships. When the left brain interferes with the right and instead tries to dominate all interaction through logic and reason, it causes the person to completely miss the boat when it comes to successful social, emotional and intimate interactions.
Sometimes, the left brain just does not want to know what is really going on emotionally as the information may be just too painful or upsetting to consider on a conscious level. Indeed, the left hemisphere may in fact deny the significance of intuitive conclusions drawn by the right half of the brain; even when someone is pointing it out.
Have you ever heard the saying that "the spouse is always the last to know?" The spouse is the last because he or she (or rather their left brain) ignored all the hints and clues normally picked up by the right half of the cerebrum.
This is compounded by the natural limitations which exist in the ability to transfer or recognize information being processed by the opposite half of the brain. That is, some forms of information cannot be shared by the right and left brain, and some forms of information cannot be perceived or even recognized by the right versus the left brain. For example, the left brain can't sing and the right hemisphere can't do math. This is the consequence of having two brains, each of which is specialized. Still, by having two brains (or rather, cerebral hemispheres), we can do twice as much.
THE RIGHT & LEFT HEMISPHERE - THE UNCONSCIOUS & CONSCIOUS MIND
It is important to emphasize that the right and left half of the brain are not completely dichotomous and share many of the same abilities. Some functions are simply processed much more efficiently and effectively in one versus the other half of the brain.
This is not surprising since for many millions of years the right and left half of the brain probably subserved many of the same functions and processed the same types of information in a similar fashion. Indeed, although the brain appears to have possessed some rudimentary temporal-sequential capabilities as long as 2 million years ago 26, both the right and left cerebral hemisphere were probably also equally adapated for processing visual-spatial information and environmental sounds. This in turn would be reflected in the activities that ancient men and women probably engaged in on a fairly equal and similar basis i.e. wondering over long distances scavenging, hunting and chasing small game, as well as gathering.
However, the capacity of the human brain to process visual spatial, distance, depth, movement, and other environmental variables, probably became enhanced even further with the onset of big game hunting about 300 thousand years ago.
Hunters had to be extremely aware of their environmental surrounding and able to read even subtle nuances which might inform them of the presence of an antelope herd, the nearness of a dangerous predator, or even the location of water. These ancient hunters would be able to distinguish via footprints and hoof marks, broken vs bent branches, the size, color, consistency and texture of feces, the smell of urine, the manner in which a twig had been broke, or the color and size of a puff of hair hanging on a branch, and so on, what was left by a large versus small, male versus female, young versus old, sick, wounded or feeble, versus strong powerful and healthy animals and would then be able to plan the hunt accordingly
In contrast, a modern man wandering perhaps upon the same path, might not even know that a single animal, much less an entire herd of beasts had passed the same way perhaps just hours before even though all the same clues are right there before him; albeit in an invisible and unreadable form.
The ancient hunter traversing his own territory knows it as well as a modern man might know his own backyard. Any changes, alterations, every broken twig and vine stands out with significance and has a story to tell.
However, the story is in images, feelings, tastes, odors, expectations, memories, and emotions. Because our very remote ancestors did not read or write, and did not speak in any manner remotely resembling the grammatical utterances of modern humans, they in fact had more brain space than modern humans to devote for performing what for them was a central aspect of their lives; functions which today are dominated by the right half of the brain and limbic system. However, a major divergence in functional capability, i.e. handedness, possibly began to exert a profound effect on how the two brains processed and responded to information well over half a million years ago and particularly during the last 50,000 years with the invention and refinement of complex tool construction.
Over 80% of our modern day population is right handed. One reason why most of us become right hand dominant is during prenatal development nerve cells and fibers in the left brain which control hand and arm movement begin to mature and grow more quickly than those from the right hemisphere 27. This is genetically programmed. We become right hand dominant because the left brain gains a competitive advantage and obtains a head start in regard to motor control and development. Still, there is more to it than that.
THE KNOWING HAND
HANDEDNESS, LANGUAGE & TEMPORAL SEQUENCING
It has been repeatedly argued by a number of investigators that language, in particular its grammatical and syntactical components, are directly related to handedness and motor control (e.g. D. Kimura, J. L. Bradshaw, N. Nettleton, M. Kinsbourne) . Among the majority of the population it is the right hand which is dominant for grasping, manipulating, exploring, writing, creating, destroying, and communicating. That is, although the left hand assists, it is usually the right which is more frequently utilized for orienting, pointing, gesturing, expressing and gathering information on the environment. The right hand appears to serve as a kind of motoric extension of language and thought in that it acts at the behest of linguistic impulses.
Moreover, while talking, most individuals display right hand/arm gestural activity which appears to accompany and even emphasize certain aspects of speech. When speaking, the areas of the brain controlling right hand use become activated. In part this is due to the spread of neural excitation from the speech area to the immediately adjacent cortical regions which control hand movement. Indeed, both occupy to some degree the closely aligned cortical space in the frontal lobe and rely upon similar neural centers in regard to programming. Hence, because they are so intimately linked, speaking triggers hand movement due to the spread of neural excitation.
NAMING, KNOWING, COUNTING, FINGER RECOGNITION & HAND CONTROL
A variety of theories have been proposed so as to explain the evolution of handedness and language. Nevertheless, from an evolutionary, phylogenetic, and ontogenetic perspective, handedness and temporal-sequential motor control probably preceded the development of language specialized nerve cells 77.
Indeed, it is first via the hand that one comes to know the world so that it may be named and identified. Hence, the infant first uses the hand to grasp various objects so they may be placed in the mouth and orally explored. As the child develops, rather than mouthing, more reliance is placed solely on the hand (as well as the visual system) so that information may be gathered through touch and manipulation.
As the child and its brain matures, instead of predominantly touching, grasping, and holding, the fingers of the hand are used for pointing at and then naming the object indicated. It is these same fingers which are later used for counting and the development of temporal-sequential reasoning; i.e. the child learns to count on his or her fingers, then to count (or name) by pointing at objects in space.
In this regard, counting, naming, object identification, finger utilization, and hand control are ontogenetically linked. In fact, these capacities seem to rely on the same neural substrates for their expression; i.e. the left inferior parietal lobe and the angular gyrus. Hence, when the inferior parietal region of the left brain are damaged, naming (anomia), object identification (agnosia -a term coined by Freud), arithmetical abilities (acalculia), finger recognition (finger agnosia) and temporal-sequential control over the hands and extremities (apraxia) are frequently compromised. Sometimes, in fact, all these symptoms may occur together and are referred to collectively as Gerstmann's Syndrome (after the doctor who first recognized this association). The presumed link is not only the hand, however, but the processing of information in temporal sequences.
For example, a patient with damaged in this area and suffering from apraxia and thus a loss of temporal and sequential coordination, would be unable to "pretend to open a tube of toothpaste, pretend to squeeze it out on a toothbrush, pretend to put it down and then brush the teeth." Instead, the apraxic person would get the order confused and may first pretend to brush the teeth and then squeeze out the paste and so on. Certainly a person with apraxia would be unable to carry out the sequences involved in complex manual tool making.
It is relationships such as these which lend considerable credence to the argument that over the course of evolution the predominant usage of the right hand enabled the left brain to develop nerve cells specialized for counting, naming, temporal-sequential processing and thus for the mediation of grammatical-syntactical speech and language.
However, it is equally important to emphasize that the social and emotional sounds of speech, those language capabilities more clearly associated with the right half of the brain and limbic system, had no doubt been employed in a complex fashion for at least a million years before the first tool was ever struck. Social and emotional sounds were the first form of true vocal communication and a language capability employed by humans and animals today.
It is complex tool making and temporal-sequential, grammatical speech that is more unique to humans, functions which are still associated with the right hand and left half of the brain.
SPECULATIONS ON TOOL MAKING & LANGUAGE
There is some evidence that non-human primates and certain mammals including some birds may have functions which tend to be more greatly concentrated in one versus the other half of their brains. However, among almost all other primates and animals about 50% tend to use their left and about 50% prefer their right limbs. Animals are neither right nor left hand dominant as are human beings. Our own human ancestors were probably also without preference until at least about 2 million years ago.
Once this preference became established the left brain began to evolve and adapt as it increased its proficiency in right hand motor control which in turn affected brain development. Tool making also evolved as did the ability to make more efficient weapons and hunting implements. Indeed, over around 2.4 to 2.6 million years ago simple stone tools were being struck (by Homo habilis, the presumed ancestor to all species of Homo including modern man) and by 100,000 years ago,with the appearance of our remote Homo sapien ancestor, Neanderthal, humans were making a variety of very simple stone tools in abundance. However, it was not until about 40,000 years ago that tool making became literally an art and evolved beyond the use of rock and stone 29.
Tool making and tool factories be they primitive or modern, require repetition and order as the implements are fashioned. First you take your bone and scrape, then you heat, then you sharpen, etc., such that a temporal sequence is established and the same type of tool can be made over and over again. Hence, by 100,000 years ago the left brain was not only dominant in regard to hand and motor control, but was beginning to become inceasing proficient at temporal and sequential processing 30. In part this increasing specialization was also related to gathering activities, an intensive full time affair which involves repeated temporal and sequential hand movement.
It is probably not unreasonable to assume that although quite primitive, the Neanderthal people had names for certain of their foods and tools as well as the implements they used to construct, gathering, or prepare them 31. Hence, if a chopper might be needed our primitive ancestor may well have been able to ask one of his compatriots to hand it to him by name.
Although admittedly such notions are quite speculative, it is seems likely that by 100,000 years ago the left hemisphere was not only continuing to become adept at motor control and temporal sequencing, but at a minimum was now employing a limited vocabulary of words 32. In fact, in addition to mimicry and its emotional-social language capabilities the right hemisphere was probably able to say the same words as well.
Nevertheless, although major differences had begun to occur the right and left half of the brain were probably still similar in many ways and language capabilities proably remained quite limited due to limitations in brain development and the poorly developed pharynx.
The ability to engage in complex conversational speech probably remained severely limited until almost 40,000 years ago with the appearance of the Cro-Magnon 33. Interestingly, the Cro-Magnons were probably as handsome, stood as tall, had fully developed vocal capabilities, and had a larger brain than present day Homo sapiens sapiens 35. These are the same people who 15-40,000 years ago left hundreds of paintings, drawings, etchings, and fine sculptures of bisons, deer, wild horses, and bears in caves and rocky cliffs of Eastern and Southern Africa (where a few scholars have speculated that they may have appeared almost 100,000 years ago), Europe, Russia, the Middle East (where they began to appear in increasing numbers about 40,000 years ago), and possibly the Americas (where the remnants of hearths and base camps, dating anywhere from 20-38,000 years ago, have recently been discovered). The Cro-magnon brought to the world complex spiritual beliefs, vivid, colorful imagery, finely developed artistic expression and pictorial language 36.
A wild acceleration in the evolution of the mind and brain possibly began to escalate about 40,000 years ago at which time mental functioning become quite complex and profound 37. Humans appear to have become self-conscious and the two halves of the brain seem to have increasingly become adept at performing new functions. People maintained a home base and built large houses with stone foundations and lived in villages sometimes including as many as 500 individuals. They sewed their own clothes, wore makeup, jewelry and personal decorations, believed in an after-life, had complex supernatural beliefs and rituals which they regularly performed. The Cro-Magnon buried their dead with flowers, clothing, ornaments, beads, head bands, necklaces, weapons, and offerings of food. They became extremely proficient at hunting, gathering and harvesting, tool making and temporal-sequential processing, had names for each other and their tools, and were working e.g. engaged in food procurement, about 2-4 days per week on average. In contrast, those who preceded them probably spent a good part of every day in the seeking of food. By 40,000 years ago they were probably capable of engaging in complex conversations and due perhaps to the increased leisure time they now enjoyed, were painting and sculpting in profusion.
With the appearance of language, profound artistic expression, self-consciousness and right and left brain functional specialization, a schism had formed in the psyche of man. Where as before there had been a more or less unified mind, now there was a new and additional form of mental processing which also gave birth to a profound creative spirit as well as the capacity to reason and form complex thoughts.
By at least 100,000 years ago during the golden age of the Neanderthals, a fragile and minimally developed linguistic consciousness probably emerged from what had been the original mind. As this linguistic consciousness evolved so too did the left brain. As language, linguistic consciousness and temporal-sequential processing increasingly came to dominate left brain mental functioning other capacities possibly became displaced. In consequence, functions that both the right and left brain had expertly performed increasingly became the sole or dominant domain of the right half of the brain., whereas language and temporal sequential processing became the hallmark of the left half of the cerbrum.
This original mind has not been discarded, however. Rather, as the left brain became increasingly associated with language and linguistic consciousness, this Original mind appears to have also evolved and to have become more intimately associated with the right cerebral hemisphere. It is probably for these reasons that among modern human beings, the right hemisphere is associated with the presumably more primitive unconscious whereas the left brain maintains what we have referred to here as the more recently evolved, language dependent, conscious mind.