ENTRIES A–Z
Philip Winn in Dictionary of Biological Psychology, 2003
The term split brain refers to a neurological condition when the main COMMISSURES connecting the two CEREBRAL HEMISPHERES have been surgically disconnected (see COMMISSURE; HEMISPHERE). The term initially described an animal preparation used in the classic work of Ronald Myers and Roger Sperry. It was subsequently applied to a small group of patients—split-brain patients—in whom, as a last resort, the CORPUS CALLOSUM (and in some cases also the ANTERIOR COMMISSURE) was sectioned in order to reduce the spread of EPILEPSY from one cerebral hemisphere into the other. Myers' studies on cats and monkeys were important because they established new and hitherto unexploited methods. There had been previous attempts to cut these main pathways between the two cerebral hemispheres but the outcome, whether in humans or animals, had seemed to be trivial with seemingly few consequences from such a major change in brain structure. With carefully controlled studies, maintaining orienting and preventing information exchange between the hemispheres through transactions with the external world, Myers & Sperry found that the split-brain animals appeared to have totally divided perception and learning. At the same time, their movements and alertness when moving about freely and their general motivation seemed to be unchanged.
Lateralization of the Contents of Memory
Robert Miller in Axonal Conduction Time and Human Cerebral Laterality, 2019
We have already seen hints that language might not be centred on the left hemisphere in a unitary fashion, when discussing American sign language. However, a role for the right hemisphere in some aspects of language has been known since the 1960s: Initially it became clear, from split-brain and hemispherectomy studies that the right hemisphere mediates important aspects of the visual recognition of words (Smith, 1966; Gazzaniga and Sperry, 1967; Gott, 1973; Levy and Trevarthan, 1977; Bergego et al., 1993). Such a function might be expected from what we have already discussed in terms of perception of complex stimuli. Subsequently, interest has grown in the differential lateralization of semantic as opposed to phonetic attributes of words. This also came initially from study of split-brain patients. For instance, Gazzaniga and Sperry (1967) found that the isolated right hemisphere was able to recognise individual words, both written or spoken (e.g. by pointing to a corresponding picture or object). However, occasionally substitutions were made between the correct word and a synonym (as though the meaning had been correctly identified rather than the word itself).
Neurosurgery And Clinical Tales
Andrew P. Wickens in A History of the Brain, 2014
The results from Sperry’s innovative experimental procedures on split-brain patients have provided some of the most fascinating and astonishing findings in the history of biological psychology. Put simply, Sperry was to demonstrate that the right and left cerebral hemispheres have different functions, specialised abilities and even distinct personalities. Thus, when they are ‘split’ from each other, the two cortices act as independent and separate ‘brains’. The first patient tested by Sperry, assisted by Gazzaniga in 1962, was a former Second World War paratrooper, known as WJ, who started having seizures after being hit over the head with a rifle butt. Over the years his fits had got progressively worse leading to a commissurotomy in 1961. Testing soon confirmed differences between the two hemispheres – especially the superiority of the left for language. For example, when Sperry and Gazzaniga presented a written word such as ‘spoon’ or ‘key’ to the left hemisphere, WJ was able to read it, vocalise it, and understand its meaning. However, no recognition occurred when the word was presented to the right hemisphere, with the patient reporting they had seen nothing other than a flash of light, or sometimes nothing at all. The left hemisphere also had the ability of writing by being able to scribble down answers to simple questions through its control over the right hand.12 This was not a skill shared by the left hand.
The effects of aerobic exercise on corpus callosum integrity: systematic review
Published in The Physician and Sportsmedicine, 2020
Paul D. Loprinzi, Jacob Harper, Toshikazu Ikuta
Integrity of the human CC is often measured via diffusion tensor imaging. Including metrics of fractional anisotropy (FA), higher values indicate greater white matter integrity. Also, calculated from axial diffusivity (AD) and radial diffusivity (RD), as well as mean diffusivity (MD), higher values indicate lesser white matter integrity. Integrity of animal (mice) CC often consists of anesthetizing the specimen to prepare brain tissue under investigation. Analysis is conducted through dissection followed by microscopic evaluation or custom-made MRI devices. Dissection of the CC has been known to result in ‘split-brain’ where two cerebral hemispheres minimally interact and exhibit independence from each other [2]. Interhemispheric connectivity provided by the CC is associated with cortical functions. For example, in the context of motor function, the CC influences bi-manual motor performance and may be involved in transferring inhibitory signals to the opposing hemisphere before and during motor execution [5,6]. Association between motor functions and interhemispheric motor fibers via the CC has been shown in adults and children [7,8]. With this in mind, maintaining the corpus callosum integrity is essential.
Treatment effects of olanzapine on homotopic connectivity in drug-free schizophrenia at rest
Published in The World Journal of Biological Psychiatry, 2018
Wenbin Guo, Feng Liu, Jindong Chen, Renrong Wu, Lehua Li, Zhikun Zhang, Huafu Chen, Jingping Zhao
The human brain exhibits homotopic interaction mediated by the commissural system, including the corpus callosum, anterior and posterior commissures, cerebellar commissures and interthalamic adhesions (Hoptman and Davidson 1994). Evidence shows that there is advantage for human hemispheres to process information bihemispherically (Belger and Banich 1992). For example, patients with forebrain commissures sectioned exhibited disconnection phenomena on divided sensory spatial field tasks (Nebes 1972). Moreover, patients with split brain showed deficits in sustained attention (Dimond 1979a, 1979b). Healthy subjects also benefited from bihemispheric processing on laterally presented information (Belger and Banich 1992). The bilateral advantage suggests that human interhemispheres will operate more efficiently with bihemispheric processing than for one hemisphere to process information alone.
Galileo’s Error: Foundations for a New Science of Consciousness
Published in Journal of the History of the Neurosciences, 2021
One wonders how Goff, with this notion of integrated system of particles, looks at clinical phenomena such as concussion, or unawareness of the ipsilesional side of space in patients suffering from visuospatial hemineglect, or the unawareness of a deficit like blindness (Anton’s syndrome) that are commonly associated with consciousness? And what about delirium, delusional states, and hallucinations? Goff does not deal with these clinical conditions, but he does discuss another remarkable phenomenon: consciousness in so-called split-brain patients. In fact, this is the only actual neuroscientific phenomenon Goff attends to in more detail. In the 1980s, the anecdote of a woman in whom the corpus callosum was split in order to control severe epileptic attacks triggered an intense dispute on consciousness. The woman reported that she would stand in front of the closet, considering what to wear, and her left hand would pick one piece of clothing and her right hand would reach for another. It seemed that each hemisphere had its own wishes, its own volition. It was argued that only the left hemisphere was able to talk about its wishes and explain its actions, whereas the right was able to perform reasonable action but simply could not communicate. What had happened to her consciousness? Did the surgery produce two consciousnesses, or did it split consciousness in two? Referring to the German panpsychist philosopher Luke Roelofs, Goff argues that what we see here is a “decombined” consciousness.
Related Knowledge Centers
- Cerebral Cortex
- Cerebral Hemisphere
- Corpus Callosotomy
- Corpus Callosum
- Optic Tract
- Somatosensory System
- Epilepsy
- Disconnection Syndrome
- Seizure
- Lateralization of Brain Function