Hemispheric Connections
The major band fibers connecting the left and the right hemisphere of the brain
The human brain is made up of the right and left hemispheres that are connected by a network of nerve axons called the corpus callosum.
The function of this band of fibers
The corpus callosum helps to assimilate the sensory, motor, and cognitive messages between the two corresponding regions in the two cerebral hemispheres. It, therefore, aids in communication between the two parts of the brain, enabling them to complement each other in function.
Crossover patterns of connection between hemispheres and body parts
Touch
In the Medulla of the brain, the nerve fibers arising from the two cerebral hemispheres intersect making the right hemisphere control the left half of the body and vice versa. Thus, a touch felt on the left hand is registered in the right hemisphere.
Hearing
The auditory nerves pick the sound waves that enter the right ear and transmits the sensory impulse to both cerebral hemispheres that integrate the information enabling one to detect the various aspects of sound such as direction, magnitude, and pitch. Even though both hemispheres receive the sensory impulse, the left hemisphere receives much of the primary information from the right ear, i.e., the primary auditory information is sent to the brain in a contralateral fashion just like messages from the rest of the body.
Vision
The rods and cones in the retina process the light entering the left eye. The sensory signal is then channeled through the optic nerve to the visual cortex in both the right and left cerebral hemispheres where it is processed further. The optic nerve from each eye branches and sends primary information to both hemispheres.
The visual pathway differs from that of the ear or touch because it does not follow the contralateral pattern. In the visual pathway, both eyes can detect half of the information in any given field of view, i.e. both the left and right field of view. The sensory information from the right field of view combines and proceed to the left hemisphere while that from the left field of view proceed to the right hemisphere.
Split-Brain Research
The part of the brain surgically cut in split-brain patients
Split brain refers to a brain condition where the corpus callosum has been severed.
The reason for this surgery
Surgical removal of whole or a part of the corpus callosum is done to reduce seizures in epileptic patients.
The case of a blindfolded split-brain patient and a fork
In a patient with the split brain, each cerebral hemisphere can learn, but it is independent of the other, i.e., one hemisphere does not experience what the other experiences or learns. Each cerebral hemisphere can sense touch. The left cerebral cortex receives information from the right side of the body. Since centers of verbal ability are located in the same hemisphere, the patient can tell the item he or she is holding.
When a fork is placed in the left hand of a blindfolded, split brain patient, he or she can sense it. The right cerebral cortex receives information from the left side of the body. However, the center for speech is located in the left hemisphere. Thus, even though the patient can detect what has been placed in his or her hand, he or she cannot verbally say what it is. However, the patient can draw, point or pick objects similar to it.
The case of a blindfolded normal patient and a fork
A person with an intact brain has the corpus callosum functioning as a communication bridge between the right and the left cerebral hemisphere. When blindfolded, he or she would not find any difficulty in identifying and verbally telling any object placed in either of his or her hands.
Language abilities of the hemispheres in split-brain patients
Nerve signals from the right part of the body are processed in the left cerebral cortex while those of the left hand are processed in the right cerebral cortex. A split-brain patient can name and describe an unseen object in the right hand, but not objects on the left hand. This observation strongly suggests that the speech area of the brain is located in the left cerebral cortex. However, the right cerebral cortex is also able to understand the language, but in a nonverbal mode.
The case of a split-brain patient and a painting of a face made out of fruits
The ability to recognize faces resides in the right hemisphere while the ability to analyze details are in the left hemisphere. Thus, when a painting of a face made out of fruits is shown to a patient in his left field of view, sensory messages are sent to the right hemisphere, enabling the patient to identify non-verbally the painting as a face.
On the contrary, if the same painting is shown to the split brain patient in his right visual field, he says that he saw a painting of fruits. The patient sees the fruits and not the face.
Conclusion
The findings indicate that the right hemisphere plays a role in nonverbal communication such as gesturing and pointing while the left hemisphere is concerned with speech. The right hemisphere is also concerned with spatial tasks, conveyance of emotions and recognition of faces while the left hemisphere focuses on the elements of the face such as mood and the expression on the face. The left hemisphere has the ability to reason, the power to invent, and the ability to interpret the world around it. It also functions as a center for math and scientific skills.