The purpose of this paper is to evaluate the correlational method as a means of examining the relationships between functions of the left and right hemisphere. I will compare the performance of people with intact brains with the performance of so-called split-brain patients. In many ways, the brains of these two groups are very similar. 1.a. The brainstem is located at the base of the brain connecting it to the spinal cord. It has many essential functions for each of its parts: the medulla, the pons, the reticular formation, and the thalamus. The medulla, the lowest part of the brainstem, ensures vital systems like the cardiovascular and respiratory systems are working properly. The pons, a round structure just above the medulla, carries information about stimuli, motor commands, and maintaining equilibrium; coordinates body movements. The reticular formation, a net like structure, involves in triggering arousal; controls alertness or sleep. Lastly, the thalamus, takes information and passes it on to the cerebral cortex, the sensory part of the brain. Moreover, there is no difference in the functionality of a normal brainstem and that of a split-brain brainstem because it’s not a part that is severed by the surgery. 1.b. In a normal brain, the hippocampus, a part of the limbic system, is located under the cerebral cortex, and is responsible for processing conscious and new memories. There are no differences in the anatomy of the normal hippocampus and that of the split-brain hippocampus. 1.c. The corpus callosum is located beneath the cerebral cortex between the right and left hemisphere, which integrate motor, sensory, and cognitive performances between the cerebral cortex on one hemisphere to the other; allows the hemispheres to communicate with each other and share information. The anatomy of the normal corpus callous of intact brains and those with split- brain surgery is different because during the surgery the corpus callosum is severed which effectively splits the right and left hemisphere and hinders that communication. 1.d. Lastly, the cerebral cortex, located above the mainstem and the limbic system, contains four major lobes of the brain; the frontal lobes, parietal lobes, temporal lobes, and occipital lobes. The frontal lobe controls important cognitive skills, such as emotional expression, decision making, problem solving, memory, speech, and sexual behaviors. The parietal lobe, which includes the two hemispheres, processes sensory information regarding the location of parts of the body as well as touch. The temporal lobe is responsible for auditory information. The occipital lobe is responsible for vision reception. There are multiple differences in the function of the cerebral cortex in a split brain and an intact brain. Since the connection between the two hemispheres of the brain is cut off, there is a lack of communication between the two sides which can affect the visual fields, speech, reasoning, and losing control of some body parts.

The split-brain patients provide scientists with a window into the normal functions of the brain. 2.a. They suffer from refractory epilepsy, or uncontrollable seizures, due to over communication between the hemispheres. Therefore, they undergo a surgical technique called corpus callosotomy, which involves the severing the corpus callosum, the main bond between the brain’s left and right hemispheres. 2.b. As a result, language function is lateralized, which can be demonstrated through different tests. For instance, since the right hemisphere is responsible for repaying information to the left side of the body. If you give a split- brain patient a ball to their left hand, they will say that they can’t see the ball because the communication of information is disturbed. 2.c.  For general populations, this conveys that any damage to the corpus callosum hampers communication between the hemispheres and thus lateralizing multiple functions.

Cognitive tests performed on split-brain patients have identified a division of labor between hemispheres. It is conceivable that functions handled by the different hemispheres will show a strong relationship in the general population, but not in split-brain patients. 3.a. The left hemisphere is active in speech production, logical reasoning, reading, and performing calculations. The right hemisphere is responsible for creativity such drawing and listening to music, as well as recognizing faces and emotions. 3.b. The hypothesis for this study is that in intact brains, there would be a strong relationship between functions performed by the right and left hemisphere. In split-brain patients, the relationship between the two hemispheres disappeared because the corpus callosum is severed and functions are lateralized to one hemisphere. 3.c. The correlational method supports laterality in split brains because it shows the extent to which there is any dominance of one hemisphere over another conveying that there is little to no communications in the hemispheres of split-brain patients. Further, if the average correlation coefficient is higher in the intact brain, as opposed to the split-brain, it shows laterality of the hemispheres.

Data were collected from a group of split-brain patients and a group from the general population to tests the hypothesis using the correlational method. Each group completed three tasks shown previously to be lateralized: (1) a vocabulary test, (2) a logical reasoning task, and (3) a face recognition task. 4.a. The vocabulary and the reasoning are lateralized to the left hemisphere while the face recognition is lateralized to the right hemisphere. 4.b. If the hypothesis is correct, then the correlation, r, in split-brain participants in all the tasks will be lower than that in intact brain participants. 4.c. Using the formula to compute the correlation coefficient between each pair of tasks the results are: for intact brain participants vocabulary and reasoning (I= 78176, II=59.576, III=1542.0002, r= 0.715), reasoning and facial recognition (I=59.576, II=116785.847, III=2299.836, r= 0.872), facial recognition and vocabulary (I=78176, II=116785.847, III=60729.58, r= 0.636). For split-brain vocabulary and reasoning (I=88909, II=95.905, III=2089.705, r=0.716), reasoning and facial recognition (I=95.905, II=108737.563, III=137.172, r= 0.042), facial recognition and vocabulary (I=88909, II=108737.563, III=137.172, r=0.345).  

The results of the correlational method were valuable in addressing the hypothesis under study. However, the future investigations may need to adopt techniques that improve upon those used here. 5.a. It was initially hypothesized that the absence of communication between the left and right hemisphere in split-brain patients results in laterality in one hemisphere, and that is supported by the data. The split-brain participants had a lower correlation coefficient in reasoning and facial recognition and in vocabulary and facial recognition very similar correlation coefficient in vocabulary and reasoning to that of intact brain participants. They clearly performed better in tasks that are lateralized to the left hemisphere while having lower coefficients within tasks that required both hemispheres. 5.b. The similar correlation, in vocabulary and reasoning in split- brain participants, however, does not fully fit the hypothesis and promotes further investigation. A possible explanation is that since vocabulary and reasoning are lateralized to the left hemisphere, then there could be a dominance in left hemisphere over the right in split- brain patients which could be researched further. 5.c. For future reference, and in order to produce accurate correlation, there should be more participants in the study. Also, future studies should be more focused on to one hemisphere at a time instead of both. However, it’s important to know that correlation doesn’t mean causation it’s only to see if there is a relationship. 5.d. Correlation studies should be used along with experiments to evaluate hypotheses. 5.e. To explore left or right hemisphere laterality in split-brain patients there should be multiple tests relevant to each hemisphere; these tests would point to either hemisphere dominance in split brain patients.