Right Hemispheric Superiority in Split-Brain Monkeys - Report Example

Article Review Lateralization in Rhesus Monkeys 5/13 This is an article review of “Right Hemispheric Superiority in Split-Brain Monkeys for Learning and Remembering Facial Discriminations.” It outlines the object of study, the background, the methodology and results, as well as suggesting avenues of future research and impact on everyday people The more psychologists understand human brain anatomy, the more we recognize its uniqueness among the animal kingdoms. The problem, however, is that there are many aspects of psychological research that could shed light on important parts of human neurological pathology, but for ethical reasons could never be tested on humans (if, for instance, it would put them in danger, harm, uncomfortable positions and so on). This means that it is increasingly important to find other animals who can serve as models in these situations. Filling in part of that gap was the purpose of the study entitled “Right-Hemispheric Superiority in Split-Brain Monkeys for Learning and Remembering Facial Discriminations,” published in Behavioral Neuroscience in 1998 by Betty A. Vermeire, Charles R. Hamilton, and Anne L. Erdmann of the California Institute of Technology. Facial recognition is something that is strongly hemisphere-correlated in humans, that is, humans process facial recognition almost exclusively in one hemisphere and not the other, something which could be unique amongst primates (Vermeire, Hamilton, Erdman 1998 p. 1048). This kind of hemispheric specialization is common in humans, but uncommon in other animals, making research on it that cannot ethically be conducted on humans difficult (Vermeire et. al 1998). The purpose of this study was to discover if rhesus monkeys also had hemispheric specialization in facial recognition, a species that would be ideal because of its social organization that requires facial recognition both to recognize individuals and mood (Vermeire et. al. 1998). If rhesus monkeys also feature hemispheric specialization as humans do, it would firstly inform understanding of human evolution and the process by which hemispheric specialization occurred, but more importantly, would allow such monkeys to serve as models for experimentation examining phenomenon involved with hemispheric specialization (Vermeire et. al. 1998 p. 1048). Though a hypothesis was not explicitly stated in the article, implicitly the hypothesis was that rhesus monkeys would show a degree of hemispheric specialization in facial recognition. The population studied was a group of twenty seven rhesus monkeys that had undergone split-brain surgery, entirely separating the two hemispheres of the brain (Vermeire et. al. 1998, 1052). These monkeys had been used for many experiments relying on the division of their hemispheres in the past several years, but each experiment was careful to give each hemisphere very similar experiences so to not allow a build-up of changes between each hemisphere, such as greater practice at memory tasks or dissecting visual cues (Vermeire et. al. 1998). Using individuals with a split brain, rather than comparing individuals, allows for control of variables related to innate talent at the tasks, and significantly increases the reliability and universality of the experiment (Vermeire et. al. 1998). Each monkey was also tested for handedness, by observing their preference when reaching for food, so this could be accounted for in any results (Vermeire et. al. 1998). The experimental design was as follows: each monkey would stand at an opaque divider with two eye holes and two arm holes (Vermeire et. al. 1998). They would then be tasked to either identify different individual rhesus monkeys, or the same rhesus monkeys with different expressions – if they were successful in identifying whether it was the same or different monkeys correctly, they would be given a reward pellet (Vermeire et. al. 1998). Each test was done fully on one side of the monkey – the memory test would be shown only through one eye hole, and the monkey would then use that arm to either touch a plate, indicating go, or refrain from touching the plate, indicating a no go situation (Vermeire et. al. 1998). Adequate steps were taken to ensure memorization had been completed before the testing began, and the testing was also repeated after a six month gap (Vermeire et. al. 1998). Data on the monkey’s success rates based on hemisphere, along with administration of the test, was all controlled by computer (Vermeire et. al. 1998). Because of the small sample size, the authors chose to present detailed raw data for each monkey, from which their results could be re-confirmed independently. The scientists then subjected this data to a variety of statistical tests, such as t-sample, standard deviation and so on. They found that as a group, the rhesus monkeys showed significantly higher aptitude at learning and recognizing facial cues on the right hemisphere compared to the left, and thus demonstrated lateralization of brain function which, while smaller in significance than found in humans, was similar in nature (Vermeire et. al. 1998). This means that these rhesus monkeys may in fact be suitable models for humans in some lateralization tests, which should allow scientists to better understand the phenomenon in humans. Conclusion This article had a sound research methodology that was backed up by decades of research practices on rhesus monkeys – everything from the basic experimental design to cage set up and data interpretation had been used successfully on similar experiments in the past. One of the biggest issues with this study is the fact that there was no way to ascertain for certain that the split-brain surgery had been successful – doing so will be impossible until these monkeys die and have an autopsy. Two monkeys did die during this study – one still had small amounts of fibers connecting the two hemispheres of the brain (Vermeire et. al. 1998). Though this is probably not enough to in any way invalidate the study, it might have called it into question somewhat. Furthermore, it is impossible to truly control for the past experimentation that these monkeys had undergone – there is a small possibility that they could have all, because of previous failures in experimentation design, had slightly different experiences on one hemisphere than the other. This, again, would be unlikely to create significant results. Finally, the greatest problem with this experiment was simply that, though the monkeys did show some lateralization of facial recognition, it was not anywhere near on the order of a human. This means that, though they might serve as a model for future research, that model will always be somewhat flawed and unable to be generalized to humans very easily. This study spawns several interesting ideas for further research. One of which would be to design testing to detect the completeness of the monkey’s split brain surgery, to ensure that all experiments they have accomplished remain valid. One could, for instance, use the same set up as this experiment, but then require the monkey to use the opposite hand to respond to stimuli: any ability to do so would demonstrate incompleteness in the division of the hemispheres. The study conducted on the monkey’s handedness also could be further developed to detect lateralization of skills in rhesus monkeys, and thus their suitability as human models. It would be interesting to see if handedness differed based on the task that needed to be accomplished: do monkeys take food with one hand, for instance, but prefer grooming with another? Or, perhaps doing an experimental design where monkeys had to use their less preferred hand to accomplish tasks for a period of time (have food only accessible on their “off hand,” for instance), and if this would cause a long term impact on their chosen handedness – when given the opportunity to use either hand, would they revert to their original preference, or use the one they were used to? This would help demonstrate whether handedness in rhesus monkeys is innate, as we believe it is in humans, or learned/acquired based on the lifestyle of the monkey. This was a highly theoretical experiment, and thus has limited direct application to the “real world” – it will mostly be useful for establishing future research. But this future research could be helpful in doing experimentation for a variety of issues that involve brain lateralization, everything from learning and dealing with fine motor skills to curing lateralized disorders such as epilepsy. Works Cited Vermeire B. A, Hamilton C.R, Erdmann A.L (1998). “Right-Hemispheric Superiority in Split-Brain Monkeys for Learning and Remembering Facial Discriminations. Behavioral Neuroscience 112.5. Read More