Throughout history, the brain has been described as the most unique and complex organ in the human body. From the dawn of civilization as we know it, humans have earnestly studied the structures and functions of the brain. Despite their efforts over the centuries, we still know very little. However, due to the early primary research work of two well known biological psychologists, Roger Sperry and Michael Gazzaniga, scholars have obtained some insight into the brain’s characteristics and functions, according to Bridget Dauphin’s online discussion (http://www.xula.edu/xulanexus/issue1/Dauphin.html). Findings from Sperry and Gazzaniga’s research have led to significant theories about the lateralization of brain function in humans. There are various theories hypothesizing that the different hemispheres may have different “personalities,” different minds and also conflicting action plans.
According to Moritz (1986), for example, hemispheric specialization is one of the major characteristics of the brain. This means that the right hemisphere has special cognitive tasks it completes well; and the left hemisphere has special cognitive tasks for which it exerts dominance in terms of processing information. Indeed, based upon the literature in neurobiology, the left side of the brain in humans controls language-related and analytical skills, while the right side dominates the areas associated with non-verbal and non-linguistic stimuli like visual and spatial tasks, pattern recognitions, musical information as well as artistic and emotional expressions. Also it should be noted that the two hemispheres exercise criss-cross lateral functions in the body which is called contralateralization. This refers to the situation in which the left brain controls the right side of the body and the right brain controls the left side (Moritz, 1986).
Carlson (1994) also discovered that split-brain studies seem to provide the evidence for the importance of criss-cross communication between the two hemispheres so that humans can process information successfully. He notes the following, as described on Dauphin’s web site:
Although different skills lie primarily within different hemispheres, the importance of communication between the two sides becomes apparent as one delves into the findings of split-brain research. This research involves studying humans and animals with their left and right hemispheres surgically separated. Such surgeries are not done for experimental purposes in human beings, but, rather, to treat specific brain disorders. For example, some split-brain surgeries have been used to treat life-threatening epilepsy that is unresponsive to drug therapy (http://www.xula.edu/xulanexus/issue1/Dauphin.html).
Therefore, based upon the work of these researchers across the world and over the course of time, the term split-brain can be defined as the outcome of a surgical procedure in which the corpus callosum connecting the two hemispheres of the brain is severed. The general definition found in various studies summarizes the whole split-brain outcome that some patients suffering from severe and violent epileptic seizures become split-brain, through a surgical operation called a corpus callosotomy. Even though it is a rare neurological procedure that is performed, the objective of the neurosurgeon is to decrease the chances of risking death, accidents and physical injuries in the lives of their epileptic patients. Therefore, a corpus callosotomy has been used to control severe and violent epileptic episodes so that affected people do not harm themselves or their families.
Neurological Behavior of Split-Brain Patients
It has been observed that people with a split-brain, when shown an image in their left visual field (the left half of what each eye sees), will be unable to verbalize what they have seen. This inability happens because the left hemisphere controls the speech mechanism in most humans on our planet, and thus, the picture from the left visual field is sent only to the right hemisphere. Since the two sides of the brain cannot communicate any more owing to the corpus callosum being severed, the patients cannot name what they are seeing. The persons can, however, pick up a corresponding object (one within the left overall visual field) with their left hand, since that hand is controlled by the right side of their brain. This is why some researchers have also speculated that the split-brain patients seem to have two minds, two natures, each hemisphere with its own special goals and unique operations (Cohen 2006: 90).
Definition of Brain Components
According to the Cognitive Psychology Group 212, the following factors describe the major components of the anatomy of the brain, and what happens if those components suffer trauma or injury.
Brainstem. The brainstem is located in the lower part of the brain and controls functions necessary for human life such as breathing, heart rate, and digestion. It connects with nerve fibers at the bottom of the brain and leads into the spinal cord nervous system.
Cerebellum. Also found in the back region of the brain, the cerebellum significantly controls balance and muscle coordination in humans. People who suffer from injuries to this area would most likely experience problems with taking care of themselves and simple walking and physical exercises.
Frontal Lobe. Since the frontal lobe is the area primarily responsible for human personality and higher cognitive processing, it is not difficult to understand how damage or injury in this area can result in transformation of people’s personality. The frontal lobe contains two very important sections, the anterior and posterior lobes. The anterior section controls the characteristics of one’s personality, whereas the posterior region dominates the execution of motor skills and coordination in humans.
Occipital Lobe. Also located in the back of the brain, the occipital lobe assists people in processing the visual information they receive from the environment. Thus, it is not surprising that damage to this region causes people to experience major vision problems and difficulty with recognizing simple objects.
Parietal Lobe. The parietal lobe works with human sensation, and, like the frontal lobe, it is divided into two sub-regions. The right parietal lobe is more visual and spatial-oriented. Therefore, any injury to the right lobe would most likely result in the patients experiencing difficulty with navigating new and even familiar environments. Likewise, any damage to the left lobe, “which is more sensory oriented, may affect a patient’s language abilities” (Cognitive Psychology 212 Group).
Temporal Lobe. Both right and left temporal lobes deal with skill-based tasks associated with humans’ comprehension of language, such as memory, interpretation and processing of auditory input, that is, what we hear in the environment. The right lobe has also been described as the component of our brains most concerned with visual memory, whereas the left lobe is most concerned with verbal memory.
Corpus Callosum. Notably, the corpus callosum connects the right and left hemispheres of the brain, and sends information between them. So it enables humans to experience life and the environment with all of their diverse stimuli, holistically. However, in the cases of split-brain patients, the connection with the corpus callosum between the two regions would have been cut (Cognitive Psychology 212 Group) causing split-brain people to manifest certain “unusual” behavior.
Background History & Research on Split-Brain Patients
Many studies have indicated that when patients initially undergo surgery to sever the connection between the right and left hemispheres, there may be no major changes; however, the findings from several experiments do document significant effects after all. Most experiments, including those done by Sperry, and Gazzangaga, involved flashing a picture to one visual field while blocking the other field. In such studies, researchers would flash a picture to the right eye to be processed by the left side of the brain, and to the left eye to be processed by the right side. Surprisingly, they found that when pictures were flashed to the right side (left brain), the patients had no trouble identifying the object in the picture, but when pictures were flashed to the left side (right brain), patients were unable to see a picture. However, when the patients were instructed to reach behind a screen to pick out the correct item, they always chose the item that had been flashed to their right brain (Cognitive Psychology Group 212).
Specifically, for example, Dauphin (2000) also indicates that in the 1960s, “Roger Sperry had begun conducting split-brain studies. Initially, he experimented on cats by severing the corpus callosum, the major bundle of axons joining the left and right hemispheres of the brain” (http://www.xula.edu/xulanexus/issue1/Dauphin.html). Dauphin advocates that Sperry’s different experiments demonstrated the significant role of the corpus callosum in transferring messages across the brain hemispheres. Two-way communication among superior capacities of the brain, such as perception, memory, and cognition is possible because of the corpus callosum. Furthermore, states Dauphin, Sperry’s research also indicated that without the corpus callosum the brain is like two separate entities, one functioning without awareness of the other (as cited in Moritz, 1986).
Looking back, “one of the first experiments involved flashing a picture of a spoon in the visual field of a patient’s right hemisphere (not shown to the left hemisphere). The subject was then instructed to select the item he had seen by touching it. With his left hand (controlled only by the right hemisphere in split-brain patients), the person reached behind a screen to examine several objects by touch and correctly chose the spoon (as cited in Moritz, 1986).
However, when asked which item was shown, the patient could not give the correct answer verbally. These results indicated that the right hemisphere contained spatial information and the left hemisphere was the source of language and analytic skills. Because the spoon was not shown to the left hemisphere, the center of language skills, it could not be verbally identified” (as cited in Teyler, 1975).
These split-brain researchers have therefore concluded that the left brain in humans must control language since the patients who had seen the pictures flashed on that side could describe the object. Since the right brain does not have a language processing center, patients were unable to produce words describing the object when it was flashed exclusively to that side. But, the right brain still understood the contents of the picture because the patients were able to pick out the object from behind the screen when instructed to do so.
Split brain patients, therefore, seem somewhat fortunate still because their medical condition of a severed callosum does not hinder their normal lives. Nevertheless, however, many have undergone some major changes soon after the surgery, as certain experiments have already established. “For the most part, split-brain patients can function normally due to other areas of the brain that assist in communication; however, some problems do surface. In the most extreme cases, the left and right sides of the body come into direct conflict. For example, one patient described his right hand struggling to pull up his pants while his left hand pushed them down. On another occasion, this man’s left hand (controlled by the emotional right hemisphere) attempted to strike his wife, while his right hand (controlled by the logical left hemisphere) tried to prevent it” (Springer and Deutsch, 1981).
In essence, according to Springer & Deutsch (1981), split-brain patients do report complaints that are not so strange. “For example, some patients experience difficulties in associating names with faces, which is due to a disconnection between verbal skills and facial recognition skills. Similarly, other patients report difficulties in handling geometrical tasks and may have trouble in geometry classes. Still others complain of a poor memory and a lack of dreaming, but these have not been verified as specifically resulting from split-brain operations.”
Springer & Deutsch (1981) also believe that even when patients do report problems, the obstacle they complain about seem very subtle. They claim that it should be noted that in addition to the corpus callosum, there are other mechanisms in the brain “that provide alternate links between the hemispheres. Also, because both hemispheres generally receive the same visual information, the perception of the world generally comes together as a whole even in split-brain patients.” Many scientific fields have benefited from Roger Sperry’s work and others in this field. Scholars now have some insight about how brain hemispheric specialization works and how various disorders and conditions can be treated in neurosurgery. Thus, it was not surprising that in 1981 Roger Perry obtained the Nobel Prize for his experimental work on the “split brain.” Perry and others have established that special tasks and functions are specific to a brain domain, either left or right.
Summary of the Functions of the Split-Brain
The left and right hemispheres of the brain have specialized functions for most people. The left hemisphere is a language centre while the right hemisphere processes spatial information. These differences are most obvious in those rare individuals whose corpus callosum was surgically severed to help control a severe form of epilepsy. Jonathan Cohen believes that humans’ minds can be described as having a mind of their own separate from mental brain function. At times they think rationally, but then they allow emotional responses to override good judgments (90). He believes that this theory can explain the contradictions so evident in daily life and our perceptions: science versus religion; facts versus intuition, and so forth.
Iaccino’s Cognitive Styles Associated with Cerebral Hemispheres
Left Hemisphere Right Hemisphere
Verbal Nonverbal, visuospatial
Sequential, temporal Simultaneous, gestalt
Western thought Eastern thought
(James F. Iaccino, 1993: 30)
According to James Iaccino (33), clinical studies on split brain patients do seem to demonstrate a dichotomy of hemispheric specialization just as in studies with normal subjects. He advocates that each hemisphere indeed has its own cognitive style as depicted in the table above.
This table shows the different functions of the right and left hemispheres of the brain. It also displays the functions of the left and right hemisphere. The left brain is better at speaking, writing, mathematical calculations, and reading, and is the primary processing center for language. The right hemisphere, on the other hand, possesses superior capabilities for pattern recognitions: recognizing faces, solving problems involving spatial relationships, symbolic reasoning, and artistic activities (33).
In summary, it is now known that the right hemisphere controls important nonverbal functions (facial discriminations and musical recognitions), yet, however, it is supported by the left hemisphere, especially in more complex visual and spatial cognitive tasks. The functional asymmetries reported for each of the hemispheres suggest that the cortical differences are mainly ones of relative (rather than absolute) specialization: namely, the left hemisphere is more language-oriented than the right, whereas the right is more visually spatial-oriented than the left. Although relatively specialized for a particular input, each hemisphere still requires the other to complement its overall functioning. Because people with split brains can not combine the information of both hemispheres, their behavior may seem pretty strange to others.
The problem that has been observed among split-brain patients was that the two hemispheres of the brain communicate with each other, and if the communication was destroyed then the functions could be handled by one hemisphere better then the two combined. These split-brain experiments proved that there was dominance in each hemisphere of the brain to perform certain tasks. Even though a connected brain can perform the tasks of both sides. They also showed that the brain is capable of performing these tasks even when the corpus callosum has been severed. Although some tasks are performed better when the brain is able to communicate between the hemispheres. Such research findings are helpful to the sciences in many instances. For instance, the split-brain research helps people understand the different parts of the brain, and how they work. Also when injuries occur to the brain, psychologists and neurosurgeons can determine the possible effects on the patients and the changes they could possible undergo. Finally, psychologists will also have a better understanding of how the human brain works.