The corpus callosum is a structure made up of nerve fibers that acts as a bridge between the two cerebral hemispheres.
When damaged by injury or disease, it can occur corpus callosum disconnection syndrome, A serious neurological disorder that causes many sensory and motor disturbances.
In this article, we explain what corpus callosum disconnection syndrome is, where the term comes from, what are its causes, and the main signs and symptoms caused by this disorder.
Corpus callosum disconnection syndrome: what is it?
Corpus callosum disconnection syndrome, also called Sperry syndromeIt is a disorder caused by damage to the corpus callosum, a structure of nerve fibers that connects the two hemispheres of the brain. The disconnection that occurs between one side of the brain and another causes the patient to experience a series of clinical signs and symptoms which constitute the “disconnection syndrome”.
The effects of interhemispheric disconnection were initially studied by German neurologist Carl Wernicke, who predicted the existence of an aphasic disconnection syndrome, resulting from the severing of connections between the posterior and anterior areas of the cortical structures responsible for language.
At the turn of the last century, German psychiatrist Hugo Liepmann also extensively studied the principle of disconnection with regard to the idea that certain apraxias (neurological disorders characterized by the inability to perform intentional, learned, or familiar movements) might be caused by it. phenomenon.
Beginning in the 1950s, Roger W. Sperry and his colleagues studied the effect of corpus callosum disconnection on animals, especially cats, showing that these may seem indistinguishable from those with healthy behavior, In most tests and under training conditions.
However, Sperry’s studies revealed that the animals, as part of some training procedures, had significant deficiencies; so that, if sensory information were allowed to have separate access to each cerebral hemisphere, each of them would be shown to have separate processes of perception, learning and memory.
After studies on animals, Norman Geschwind, Mishkin and other behavioral scientists began to study the effect of disconnection (intra- and interhemispheric) in humans, building models of disconnection syndromes that they demonstrated the existence of a functional and structural interdependence between different neocortical regions.
Physiology and functions of the corpus callosum
The cerebral cortex is interconnected by three types of nerve fibers: projection fibers, which include ascending and descending fibers running from and to the neocortex to other regions such as the trunk and spinal cord; association fibers, which include short and long fibers that connect different areas of the neoscort that are distant from each other; and the commissural fibers, which connect the cerebral hemispheres, such as those of the corpus callosum, among others.
The neurons of the corpus callosum exert their action, both inhibitory and excitatory, by means of interneurons. Through the corpus callosum, information generated in one hemisphere flows to the other, and the different responses that occur when activated simultaneously are coordinated. Each cerebral hemisphere is capable of locally and selectively modulating the functioning of homologous regions of the opposite band.
The corpus callosum participates in many functions; for example, in the transfer of sensorimotor information; in the transfer of semantic information through the verbalization (left hemisphere) of an object that has been touched with the left hand (right hemisphere); or in the transfer of learning.
In this regard, several studies have shown that each hemisphere can learn to visually discriminate information that reaches the contralateral hemisphere. However, this learning disappears after the injury or comisurotomy.
Corpus callosum disconnection syndrome this can be due to several causes, including injuries to this brain structure, Heart attack (posterior, anterior or affecting transcallous fibers), traumatic brain injury (edema, ecchymosis, ecchymosis or axonal injury), tumors, malformations and neurological disorders such as Marchiafava Bignami disease.
Symptoms and signs
Regarding the clinical signs and symptoms that a disconnection syndrome can cause, these can be divided into two groups: treble, which is observed in the first days or weeks after disconnection; and chronic, which occur after 6 months lesion and can be detected by methods such as dichotomous listening and tachistoscope. These are the most common:
Acute signs and symptoms
Among the most common signs and symptoms of corpus callosum disconnection syndrome are:
- Transient silence.
- Indifference to external stimulation.
Left unilateral ideomotor apraxia.
- Underutilization of the left hand.
- “Aberrant” behavior of the left hand (diagonal dyspraxia)
Chronic signs and symptoms
These are the most common chronic signs and symptoms that appear after 6 months after disconnection of the corpus callosum:
- Modification of the processing of the somesthetic data (e.g. inability to point the hand towards the contralateral site of the body affected by the examiner)
- Impaired processing of visual information (inability to recognize an image projected on the right side after being repeatedly projected on the left side)
- Alterations in the denomination: tactile anomy of the left hand, naming problems in simultaneous bilateral condition, left visual anomy, left alexia, hemialexia, left auditory anomy, right olfactory anomy and alexithymia.
- Disorders of gestural actions: bimanual coordination problems, left unilateral apraxia, difficulty imitating gestural sequences, foreign hand sign, diagonal apraxia, optic cross ataxia and right constructive apraxia.
- Memory problems (secondary to the involvement of the callous fibers that connect the two hippocampi).
Research by Roger Sperry and Michael Gazzaniga in patients with hemispheric disconnection due to damage to their corpus callosum has shown that these people seem to experience a division of consciousness: The left and right sides of your brain appear to be “aware” and able to respond to stimuli independently.
Since this phenomenon began to be studied, it has been speculated that people with a “divided brain” may report seeing a stimulus in their left visual field, but using only their left hand and not their right. And they can signal a stimulus in their right visual field only with their right hand, but also verbally. This phenomenon occurs because the tongue is usually found in the left hemisphere of the brain, And this hemisphere receives visual information from the correct visual field.
However, a recent study by Pinto et al. found evidence that patients with a divided brain are able to signal the presence of stimuli in the left or right visual field using any hand, and can do so verbally as well. These new findings suggest that the cortical disconnection between the hemispheres does not appear to lead to two “independent conscious agents” in the brain.
However, patients had certain deficits, such as the inability to manifest whether two stimuli presented on opposite sides of the visual field were the same or different, suggesting that although the interhemispheric disconnection does not appear to affect their consciousness, the transfer of information between the cerebral hemispheres has been amended.
- Lassonde, M. (1994). Disconnection syndrome in callus agenesis. In Callosal Agenesis (pp. 275-284). Springer, Boston, MA.
- Pinto, Y., Neville, DA, Otten, M., Corballis, PM, Lamme, VA, De Haan, EH, … and Fabri, M. (2017). Divided brain: divided perception but undivided consciousness. Brain, 140 (5), 1231-1237.
- Thompson, PM, Narr, KL, Blanton, RE and Toga, AW (2003). Mapping of structural alterations of the corpus callosum in the brain. The parallel brain: the cognitive neuroscience of the corpus callosum 93.