callosum, through which they communicate and coordinate actions and decisions. communication and coordination between the two hemispheres is essential because each hemisphere has some separate functions. the right hemisphere of the cortex excels at nonverbal and spatial tasks, whereas the left hemisphere is more dominant in verbal tasks, such as speaking and writing. the right hemisphere controls the primary sensory functions of the left side of the body. in a cognitive sense the right hemisphere is responsible for recognizing objects and timing, and in an emotional sense it is responsible for empathy, humour and depression. on the other hand, the left hemisphere controls the primary sensory functions of the right side of the body and is responsible for scientific and maths skills, and logic. the extent of specialised brain function by an area remains under investigation. it is claimed that the difference between the two hemispheres is that the left hemisphere is "analytic" or "logical" while the right hemisphere is "holistic" or "intuitive." many simple tasks, especially comprehension of inputs, require functions that are specific to both the right and left hemispheres and together form a one direction systematised way of creating an output through the communication and coordination that occurs between hemispheres. role of the corpus callosum the corpus callosum is a structure in the brain along the longitudinal fissure that facilitates much of the communication between the two hemispheres. this structure is composed of white matter: millions of axons that have their dendrites and terminal boutons projecting in both the right and left hemisphere. however, there is evidence that the corpus callosum may also have some inhibitory functions. post-mortem research on human and monkey brains shows that the corpus callosum is functionally organised. it proves that the right hemisphere is superior for detecting faces. this organisation results in modality-specific regions of the corpus callosum that are responsible for the transfer of different types of information. research has revealed that the anterior midbody transfers motor information, the posterior midbody transfers somatosensory information, the isthmus transfers auditory information and the splenium transfers visual information. although much of the interhemispheric transfer occurs at the corpus callosum, there are trace amounts of transfer via subcortical pathways. studies of the effects on the visual pathway on split-brained patients has revealed that there is a redundancy gain (the ability of target detection to benefit from multiple copies of the target) in simple reaction time. in a simple response to visual stimuli, split-brained patients experience a faster reaction time to bilateral stimuli than predicted by model. a model proposed by iacoboni et al. suggests split-brained patients experience asynchronous activity that causes a stronger signal, and thus a decreased reaction time. iacoboni also suggests there exists dual attention in split-brained patients, which is implying that each cerebral hemisphere has its own attentional system. an alternative approach taken by reuter-lorenz et al. suggests that enhanced redundancy gain in the split brain is primarily due to a slowing of responses to unilateral stimuli, rather than a speeding of responses to bilateral ones. it is important to note that the simple reaction time in split-brained patients, even with enhanced redundancy gain, is slower than the reaction time of normal adults. functional plasticity following a stroke or other injury to the brain, functional deficiencies are common. the deficits are expected to be in areas related to the part of the brain that has been damaged; if a stroke has occurred in the motor cortex, deficits may include paralysis, abnormal posture, or abnormal movement synergies. significant recovery occurs during the first several weeks after the injury. however, recovery is generally thought not to continue past 6 months. if a specific region of the brain is injured or destroyed, its functions can sometimes be transferred and taken over by a neighbouring region. there is little functional plasticity observed in partial and complete callosotomies; however, much more plasticity can be seen in infant patients receiving a hemispherectomy, which suggests that the opposite hemisphere can adapt some functions typically performed by its opposite pair. in a study done by anderson, it proved a correlation between the severity of the injury, the age of the individual and their cognitive performance. it was evident that there was more neuroplasticity in older children, even if their injury was extremely severe, than infants who suffered moderate brain injury. in some incidents of any moderate to severe brain injury, it mostly causes developmental impairments and in some of the most severe injuries it can cause a profound impact on their development that can lead to long-term cognitive effects. in the aging brain, it is extremely uncommon for neuroplasticity to occur; "olfactory bulb and hippocampus are two regions of the mammalian brain in which mutations preventing adult neurogenesis were never beneficial, or simply never occurred" (anderson, 2005). corpus callosotomy corpus callosotomy is a surgical procedure that sections the corpus callosum, resulting in either the partial or complete disconnection between the two hemispheres. it is typically used as a last resort measure in treatment of intractable epilepsy. the modern procedure typically involves only the anterior third of the corpus callosum; however, if the epileptic seizures continue, the following third is lesioned prior to the remaining third if the seizures persist. this results in a complete callosotomy in which most of the information transfer between hemispheres is lost. due to the functional mapping of the corpus callosum, a partial callosotomy has less detrimental effects because it leaves parts of the corpus callosum intact. there is little functional plasticity observed in partial and complete callosotomies on adults, the most neuroplasticity is seen in young children but not in infants. it is known that when the corpus callosum is severed during an experimental procedure, the experimenter can ask each side of the brain the same question and receive two different answers. when the experimenter asks the right visual field/left hemisphere what they see the participant will respond verbally, whereas if the experimenter asks the left visual field/right hemisphere what they see the participant will not be able to respond verbally but will pick up the appropriate object with their left hand. memory it is known that the right and the left hemisphere have different functions when it comes to memory. the right hemisphere is better at recognizing objects and faces, recalling knowledge that the individual has already learned, or recalling images already seen. the left hemisphere is better at mental manipulation, language production, and semantic priming but was more susceptible to memory confusion than the right hemisphere. the main issue for individuals that have undergone a callosotomy is that because the function of memory is split into two major systems, the individual is more likely to become confused between knowledge they already know and information that they have only inferred. in tests, memory in either hemisphere of split-brained patients is generally lower than normal, though better than in patients with amnesia, suggesting that the forebrain commissures are important for the formation of some kinds of memory. this suggests that posterior callosal sections that include the hippocampal commissures cause a mild memory deficit (in standardised free-field testing) involving recognition. control in general, split-brained patients behave in a coordinated, purposeful and consistent manner, despite the independent, parallel, usually different and occasionally conflicting processing of the same information from the environment by the two disconnected hemispheres. when two hemispheres receive competing stimuli at the same time, the response mode tends to determine which hemisphere controls behaviour. often, split-brained patients are indistinguishable from normal adults. this is due to the compensatory phenomena; split-brained patients progressively acquire a variety of strategies to get around their interhemispheric transfer deficits. one issue that can happen with their body control is that one side of the body is doing the opposite of the other side called the intermanual effect. attention experiments on covert orienting of spatial attention using the posner paradigm confirm the existence of two different attentional systems in the two hemispheres. the right hemisphere was found superior to the left hemisphere on modified versions of spatial relations tests and in locations testing, whereas the left hemisphere was more object based. the components of mental imagery are differentially specialised: the right hemisphere was found superior for mental rotation, the left hemisphere superior for image generation. it was also found that the right hemisphere paid more attention to landmarks and scenes whereas the left hemisphere paid more attention to exemplars of categories. case studies of split-brain patients patient wj patient wj was the first patient to undergo a full corpus callosotomy in 1962, after experiencing fifteen years of convulsions resulting from grand mal seizures. he was a world war ii paratrooper who was injured at 30 years old during a bombing raid jump over the netherlands, and again in a prison camp following his first injury. after returning home, he began to suffer from blackouts in which he would not remember what he was doing or where, and how or when he got there. at age 37, he suffered his first generalised convulsion. one of his worst episodes occurred in 1953, when he suffered a series of convulsions lasting for many days. during these convulsions, his left side would go numb and he would recover quickly, but after the series of convulsions, he never regained complete feeling on his left side. before his surgery, both hemispheres functioned and interacted normally, his sensory and motor functions were normal aside from slight hypoesthesia, and he could correctly identify and understand visual stimuli presented to both sides of his visual field. during his surgery in 1962, his surgeons determined that no massa intermedia had developed, and he had undergone atrophy in the part of the right frontal lobe exposed during the procedure. his operation was a success, in that it led to decreases in the frequency and intensity of his seizures. patient jw funnell et al. (2007) tested patient jw some time before june 2006. they described jw as a right-handed male who was 47 years old at the time of testing. he successfully completed high school and has no reported learning disabilities. he had his first seizure at the age of 16 and the age of 25, he underwent a two-stage resection of the corpus callosum for relief of intractable epilepsy. complete sectioning of the corpus callosum has been confirmed by mri. post-surgical mri also revealed no evidence of other neurological damage. funnell et al.'s (2007) experiments were to determine each of jw's hemisphere's ability to perform simple addition, subtraction, multiplication and division. for example, in one experiment, on each trial, they presented an arithmetic problem in the center of the screen for 1 second, followed by a central cross hair jw was to look at. after 1 more second, funnell et al. presented a number to one or the other hemisphere/visual field for 150 ms—too fast for jw to move his eyes. randomly in half the trials, the number was the correct answer; in the other half of the trials it was the incorrect answer. with the hand on the same side as the number, jw pressed one key if the number was correct and another key if the number was incorrect. funnell et al.'s results were that performance of the left hemisphere was highly accurate (around 95%)—much better than performance of the right hemisphere, which was at chance for subtraction, multiplication, and division. nevertheless the right hemisphere showed better than chance performance for addition (around 58%). turk et al. (2002) tested hemispheric differences in jw's recognition of himself and of familiar faces. they used faces that were composites of jw's face and dr. michael gazzaniga's face. composites ranged from 100% jw, through 50% jw and 50% gazzaniga, to 100% gazzaniga. jw pressed keys to say whether a presented face looked like him or gazzaniga. turk et al.concluded there are cortical networks in the left hemisphere that play an important role in self-recognition. patient vp patient vp is a woman who underwent a two-stage callosotomy in 1979 at the age of 27. although the callosotomy was reported to be complete, follow-up mri in 1984 revealed spared fibers in the rostrum and splenium. the spared rostral fibers constituted approximately 1.8% of the total cross-sectional area of the corpus callosum and the spared splenial fibers constituted approximately 1% of the area. vp's postsurgery