split-brain split-brain split-brain or callosal syndrome is a type of disconnection syndrome when the corpus callosum connecting the two hemispheres of the brain is severed to some degree. it is an association of symptoms produced by disruption of, or interference with, the connection between the hemispheres of the brain. the surgical operation to produce this condition (corpus callosotomy) involves transection of the corpus callosum, and is usually a last resort to treat refractory epilepsy. initially, partial callosotomies are performed; if this operation does not succeed, a complete callosotomy is performed to mitigate the risk of accidental physical injury by reducing the severity and violence of epileptic seizures. before using callosotomies, epilepsy is instead treated through pharmaceutical means. after surgery, neuropsychological assessments are often performed. after the right and left brain are separated, each hemisphere will have its own separate perception, concepts, and impulses to act. having two "brains" in one body can create some interesting dilemmas. when one split-brain patient dressed himself, he sometimes pulled his pants up with one hand (that side of his brain wanted to get dressed) and down with the other (this side did not). he also reported to have grabbed his wife with his left hand and shaken her violently, at which point his right hand came to her aid and grabbed the aggressive left hand. however, such conflicts are very rare. if a conflict arises, one hemisphere usually overrides the other. when split-brain patients are shown an image only in the left half of each eye's visual field, they cannot vocally name what they have seen. this is because the image seen in the left visual field is sent only to the right side of the brain (see optic tract), and most people's speech-control center is on the left side of the brain. communication between the two sides is inhibited, so the patient cannot say out loud the name of that which the right side of the brain is seeing. a similar effect occurs if a split-brain patient touches an object with only the left hand while receiving no visual cues in the right visual field; the patient will be unable to name the object, as each cerebral hemisphere of the primary somatosensory cortex only contains a tactile representation of the opposite side of the body. if the speech-control center is on the right side of the brain, the same effect can be achieved by presenting the image or object to only the right visual field or hand. the same effect occurs for visual pairs and reasoning. for example, a patient with split brain is shown a picture of a chicken foot and a snowy field in separate visual fields and asked to choose from a list of words the best association with the pictures. the patient would choose a chicken to associate with the chicken foot and a shovel to associate with the snow; however, when asked to reason why the patient chose the shovel, the response would relate to the chicken (e.g. "the shovel is for cleaning out the chicken coop"). history early anatomists, such as galen (129 – c. 216 ce) and vesalius (1514 – 1564 ce), identified the corpus callosum. they generally described its function as a structure holding together the two halves of the brain. in 1784, félix vicq-d'azyr described the corpus callosum as allowing communication between the two halves of the brain. he proposed that eliminating the corpus callosum would divide the brain into two independent parts. in 1892, joseph jules dejerine reported symptoms in a person who had destruction of part of the corpus callosum (along with damage to the visual cortex: inability to read while retaining the ability to write, now referred to as pure alexia or as dejerine syndrome. in 1908, hugo liepmann observed left-sided apraxia (a motor disorder of motor planning to perform tasks or movements) and agraphia (loss of the ability to communicate through writing) following a lesion in the corpus callosum. according to vaddiparti et al. (2021), the first surgical cuts to the corpus callosum, partial corpus callosotomy, were made by neurosurgeon walter dandy in order to access and to remove tumors in the pineal gland. in 1936, dandy described three cases in which he cut the corpus callosum from its posterior (towards the back of the head) across about two thirds of its width. he described these cuts as "bloodless" and that "no symptoms follow .. division" of the corpus callosum. he concluded that his operations "dispose ... of the extravagant claims to function of the corpus callosum" (p. 40). prior to the 1960s, research on people with certain brain injuries led to the notion that there is a "language center" only in the left hemisphere of the brain. for example, people with lesions in two specific areas of the left hemisphere lost their ability to talk, to read, and to understand speech. roger sperry and his colleagues pioneered research showing that creating another lesion (done to relieve otherwise untreatable epilepsy), in the connections between the left and right hemispheres, revealed that the right hemisphere can allow people to read, to understand speech, and to say some simple words. research over the next twenty years showed that the disconnected right hemisphere is superior to the disconnected left hemisphere in allowing people to understand spatial information (such as maps), music, and emotions, whereas the disconnected left hemisphere is superior in allowing analytical thinking, talking, reading, and understanding speech. this research led to a nobel prize in physiology or medicine for sperry in 1981. sperry's initial colleagues included his caltech phd students, michael gazzaniga and jerre levy. even though sperry is considered the founder of split-brain research, gazzaniga's clear summaries of their collaborative work are consistently cited in psychology texts. in sperry and gazzaniga's "the split brain in man" experiment published in scientific american in 1967 they attempted to explore the extent to which two halves of the human brain were able to function independently and whether or not they had separate and unique abilities. they wanted to examine how perceptual and intellectual skills were affected in someone with a split-brain. at caltech, gazzaniga worked with sperry on the effects of split-brain surgery on perception, vision and other brain functions. the surgery, which was a treatment for severe epilepsy, involved severing the corpus callosum, which carries signals between the left-brain hemisphere, the seat of speech and analytical capacity, and the right-brain hemisphere, which helps recognize visual patterns. at the time this article was written, only ten patients had undergone the surgery to sever their corpus callosum (corpus callosotomy). four of these patients had consented to participate in sperry and gazzaniga's research. after the corpus callosum severing, all four participants' personality, intelligence, and emotions appeared to be unaffected. however, the testing done by sperry and gazzaniga showed the subjects demonstrated unusual mental abilities. the researchers created different types of tests to analyze the range of cognitive capabilities of the split-brain subjects. these included tests of their visual stimulation abilities, a tactile stimulation situation, and a test that involved both visual and tactile information. visual test the first test started with a board that had a horizontal row of lights. the subject was told to sit in front of the board and stare at a point in the middle of the lights, then the bulbs would flash across both the right and left visual fields. when the patients were asked to describe afterward what they saw, they said that only the lights on the right side of the board had lit up. next, when sperry and gazzaniga flashed the lights on the right side of the board on the subjects left side of their visual field, they claimed not to have seen any lights at all. when the experimenters conducted the test again, they asked the subjects to point to the lights that lit up. although subjects had only reported seeing the lights flash on the right, they actually pointed to all the lights in both visual fields. this showed that both brain hemispheres had seen the lights and were equally competent in visual perception. the subjects did not say they saw the lights when they flashed in the left visual field even though they did see them because the center for speech is located in the brain's left hemisphere. this test supports the idea that in order to say one has seen something, the region of the brain associated with speech must be able to communicate with areas of the brain that process the visual information. tactile test in a second experiment, sperry and gazzaniga placed a small object in the subject's right or left hand, without being able to see (or hear) it. placed in the right hand, the isolated left hemisphere perceived the object and could easily describe and name it. however, placed in the left hand, the isolated right hemisphere could not name or describe the object. questioning this result, the researchers found that the subjects could later match it from several similar objects; tactile sensations limited to the right hemisphere were accurately perceived but could not be verbalized. this further demonstrated the apparent location (or lateralization) of language functions in the left hemisphere. combination of both tests in the last test the experimenters combined both the tactile and visual test. they presented subjects with a picture of an object to only their right hemisphere, and subjects were unable to name it or describe it. there were no verbal responses to the picture at all. if the subject however was able to reach under the screen with their left hand to touch various objects, they were able to pick the one that had been shown in the picture. the subjects were also reported to be able to pick out objects that were related to the picture presented, if that object was not under the screen. sperry and gazzaniga went on to conduct other tests to shed light on the language processing abilities of the right hemisphere as well as auditory and emotional reactions as well. the significance of the findings of these tests by sperry and gazzaniga were extremely telling and important to the psychology world. their findings showed that the two halves of the brain have numerous functions and specialized skills. they concluded that each hemisphere really has its own functions. one's left hemisphere of the brain is thought to be better at writing, speaking, mathematical calculation, reading, and is the primary area for language. the right hemisphere is seen to possess capabilities for problem solving, recognizing faces, symbolic reasoning, art, and spatial relationships. roger sperry continued this line of research up until his death in 1994. michael gazzaniga continues to research the split-brain. their findings have been rarely critiqued and disputed, however, a popular belief that some people are more "right-brained" or "left-brained" has developed. in the mid-1980s jarre levy, a psychobiologist at the university of chicago, had set out and been in the forefront of scientists who wanted to dispel the notion we have two functioning brains. she believes that because each hemisphere has separate functions that they must integrate their abilities instead of separating them. levy also claims that no human activity uses only one side of the brain. in 1998 a french study by hommet and billiard was published that questioned sperry and gazzaniga's study that severing the corpus callosum actually divides the hemispheres of the brain. they found that children born without a corpus callosum demonstrated that information was being transmitted between hemispheres, and concluded that subcortical connections must be present in these children with this rare brain malformation. they are unclear about whether these connections are present in split-brain patients though. another study by parsons, gabrieli, phelps, and gazzaniga in 1998 demonstrated that split-brain patients may commonly perceive the world differently from the rest of us. their study suggested that communication between brain hemispheres is necessary for imaging or simulating in your mind the movements of others. morin's research on inner speech in 2001 suggested that an alternative for interpretation of commissurotomy according to which split-brain patients exhibit two uneven streams of self-awareness: a "complete" one in the left hemisphere and a "primitive" one in the right hemisphere. hemispheric specialization the two hemispheres of the cerebral cortex are linked by the corpus