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Split-Brain Psychology Essay, Research Paper

Split-Brain Psychology

A Paper by: David Norelid

Imagine being asked to sing “Mary Had a Little Lamb” and not being able to remember the words but only being able to hum the tune, or knowing the full lyrics, but only being able to bellow out what most closely resembles the cry of an abandoned calf. You cannot sing and remember the words at the same time because your brain hemispheres have been severed from each other. Imagine trying to play the piano, while one hand wants to play Rachmaninov, and the other wants to play major and minor scales. There are countless people suffering through these problems everyday because they underwent a surgical treatment for epilepsy. Although these problems are terribly debilitating to the patients, they have opened a completely new source of boundless information for neurobiologists trying to figure out the effect of the mind on the body, and vice versa. In this paper we will try to present the surgical procedure known as the split-brain operation and its effects on the individuals performance.

In a normal brain, stimuli entering one hemisphere is rapidly communicated by way of the corpus callosum to the other hemisphere, so the brain functions as a unit. When the corpus callosum of an individual is severed, leaving a split brain, the two hemispheres cannot communicate. In some forms of epilepsy a seizure will start in one hemisphere, triggering a massive discharge of neurons through the corpus callosum and into the second hemisphere. In an effort to prevent such massive seizures in severe epileptics, neurosurgeons can surgically sever the corpus callosum, a procedure called a commissurotomy. If one side of the brain can no longer stimulate the other, the likelihood of severe epileptic seizures is greatly reduced.

In a cerebral commissurotomy, the surgeon opens the skull, lays back the brain’s coverings and, with a tool called a cerebral retractor, exposes the corpus callosum between the two hemispheres. The doctor snips through the corpus callosum, severing communication between the hemispheres and preventing the transfer of seizures.

There are two hemispheres in your brain, the right and the left. At first glance, these hemispheres appear to be mirror images of one another, but closer examination reveals that they are highly specialized regions that serve differing functions.

The left hemisphere governs our ability to express ourselves in language. In over 95% of right-handed people, the left hemisphere is dominant for speech. The figure is somewhat lower for left handers, approximately 70%, but still highly significant. The left hemisphere is better then the right at recognizing sequences of words and letters. It controls our logic, our reasoning, and our analytical thought processes. It can focus on details, however it has difficulty comprehending the whole picture.

The perceptual functions of the right hemisphere are more specialized for the analysis of space and geometrical shapes and forms, elements that are all present at the same time (not sequential like language). The right hemisphere is the creative half; it can “see” the whole out of parts, thus allowing us to connect puzzle parts together. The right hemisphere also plays and important role in the comprehension of emotion. In an experiment where subjects were shown pictures of faces with strong facial expression, the right hemisphere was able to discern the expression more accurately then the left hemisphere. In addition, an experiment was done where subjects listened to verbal messages said with different emotions. The messages were presented to each ear separately. When presented to the left hemisphere, the subject was more accurate concerning the verbal content of the message. However, the right hemisphere was more accurate at identifying the emotional tone of the voice.

Ehrenwald has classified important differences between the hemispheres. This information is best expressed as a table:

Table 1: General Left-right hemisphere attributes

Left Right

Thinking Abstract, linear, analytic Concrete, holistic

Cognitive style Rational, logical Intuitive, artistic

Language Rich vocabulary, good grammar and syntax; pose no grammar, syntax; prosody, poor vocabulary metaphoric, verse

Executive capacity Introspection, will, initiative, sense of self, focus on trees Low sense of self, low initiative, focus on forest

Specialized functions Reading, writing, arithmetic, sensory-motor skills; inhibits psi Three i’s, music, rich dream imagery, good face and gestalt recognition, open to psi

Time experience Sequentially ordered, measured “Lived” time, primitive time sense

Spatial orientation Relatively poor Superior, also for shapes, wire figures

Psychoanalytic aspects Secondary process, ego functions, consciousness; superego? Primary process, dream-work, free assoc. hallucinations?

Ideal prototype Aristotle, Appollonian mode, Marx, Freud, Koestler’s Commissar Plato, Dionysian mode, Nietzsche, Jung Koestler’s Yogi

There are two major information pathways by which information of the peripheral nervous system and the central nervous system are exchanged: the somatosensory and the motor control pathways. Some general functions of each system can be separated and described, but these two pathways influence one another in many ways. It is difficult to say, “this is how somatosensory information travels, and this is how motor information travels,” because both information pathways have influences over one another. The following is a very basic summary of the information pathways for both sensory and motor systems. This should provide you with an understanding of how a normal brain communicates with the body, which in turn will help you better understand how

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