Lingesha

Functional disconnection is the disintegrated function in the brain in the absence of anatomical damage, in distinction to physical disconnection of the
cerebral hemispheres The vertebrate cerebrum (brain) is formed by two cerebral hemispheres that are separated by a groove, the longitudinal fissure. The brain can thus be described as being divided into left and right cerebral hemispheres. Each of these hemispheres ...
by surgical resection, trauma or
lesion A lesion is any damage or abnormal change in the tissue of an organism, usually caused by disease or trauma. ''Lesion'' is derived from the Latin "injury". Lesions may occur in plants as well as animals. Types There is no designated classif ...
. Applications have included alexia without
agraphia Agraphia is an acquired neurological disorder causing a loss in the ability to communicate through writing, either due to some form of motor dysfunction or an inability to spell. The loss of writing ability may present with other language or neuro ...

dyslexia Dyslexia, also known until the 1960s as word blindness, is a disorder characterized by reading below the expected level for one's age. Different people are affected to different degrees. Problems may include difficulties in spelling words, r ...
,
persistent vegetative state A persistent vegetative state (PVS) or post-coma unresponsiveness (PCU) is a disorder of consciousness in which patients with severe brain damage are in a state of partial arousal rather than true awareness. After four weeks in a vegetative stat ...
and
minimally conscious state A minimally conscious state (MCS) is a disorder of consciousness distinct from persistent vegetative state and locked-in syndrome. Unlike persistent vegetative state, patients with MCS have partial preservation of conscious awareness. MCS is a ...
as well as
autistic spectrum The autism spectrum, often referred to as just autism or in the context of a professional diagnosis autism spectrum disorder (ASD) or autism spectrum condition (ASC), is a neurodevelopmental condition (or conditions) characterized by difficulti ...
disorders.

Functional disconnection itself is not a medically recognized condition. It is a theoretical concept used to facilitate research into the causes and symptoms within recognized conditions.

History

In 1977, Witleson reported that developmental dyslexia may be associated with (i) bi-hemisphere representation of spatial functions, in contrast to the unitary right hemisphere control of these functions observed in normal individuals. The bilateral neural involvement in spatial processing may interfere with the

left hemisphere The lateralization of brain function is the tendency for some neural functions or cognitive processes to be specialized to one side of the brain or the other. The median longitudinal fissure separates the human brain into two distinct cerebr ...

's processing of its own specialized functions and result in deficient

linguistic Linguistics is the scientific study of human language. It is called a scientific study because it entails a comprehensive, systematic, objective, and precise analysis of all aspects of language, particularly its nature and structure. Linguis ...

, sequential

cognitive process Cognition refers to "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, thought, ...

ing and in overuse of the spatial, holistic

cognitive Cognition refers to "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, thought ...

mode, reflecting a functional disconnection syndrome in these individuals confirmed by Leisman in the 1980s and in the 2000s. The concept of functional disconnection developed further with Stachowiak and Poeck in 1976. who reported on a case in 1976 of a 67-yr-old male with

hemianopia Hemianopsia, or hemianopia, is a loss of vision or blindness ( anopsia) in half the visual field, usually on one side of the vertical midline. The most common causes of this damage are stroke, brain tumor, and trauma. This article deals only ...

resulting from a

cerebrovascular accident Stroke (also known as a cerebrovascular accident (CVA) or brain attack) is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, d ...

resulting in pure alexia and a color naming deficit that he suggested was due to a functional disconnection mechanism. He noted that the underlying disconnection mechanism is improved by the facilitating effect of unblocking methods (in the

tactile Tactile may refer to: * Tactile, related to the sense of touch * Haptics (disambiguation) * Tactile (device), a text-to-braille translation device See also * Tangibility, in law * Somatosensory system In physiology, the somatosensory system ...

, somesthetic, auditory, and

visual system The visual system comprises the sensory organ (the eye) and parts of the central nervous system (the retina containing photoreceptor cells, the optic nerve, the optic tract and the visual cortex) which gives organisms the sense of sight ...

s), so that pathways other than the one impaired by the brain lesion are used. In 1998, Fritson presented a mechanistic account of how dysfunctional integration among neuronal systems arises, based on the central role played by

synaptic plasticity In neuroscience, synaptic plasticity is the ability of synapses to strengthen or weaken over time, in response to increases or decreases in their activity. Since memories are postulated to be represented by vastly interconnected neural circui ...

in shaping the connections. He hypothesized that the pathophysiology of

schizophrenia Schizophrenia is a mental disorder characterized by continuous or relapsing episodes of psychosis. Major symptoms include hallucinations (typically hearing voices), delusions, and disorganized thinking. Other symptoms include social wi ...

is expressed at the level of modulation of associative changes in synaptic efficacy; specifically the modulation of plasticity in those brain systems responsible for emotional learning and emotional memory in the postnatal period. This modulation is mediated by ascending neurotransmitter systems that: (i) have been implicated in schizophrenia; and (ii) are known to be involved in consolidating synaptic connections during learning. The pathophysiology results in a disruption of the reinforcement of

adaptive behavior Adaptive behavior is behavior that enables a person (usually used in the context of children) to cope in their environment with greatest success and least conflict with others. This is a term used in the areas of psychology and special education ...

consistent with the disintegrative aspects of the disorder. Kim and colleagues in 2003 further described the disconnection hypothesis in schizophrenia as the result of a prefrontal-

parietal lobe The parietal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The parietal lobe is positioned above the temporal lobe and behind the frontal lobe and central sulcus. The parietal lobe integrates sensory informa ...

functional disconnection, particularly prefrontal dissociation and abnormal prefrontal- parietal interaction during

working memory Working memory is a cognitive system with a limited capacity that can hold information temporarily. It is important for reasoning and the guidance of decision-making and behavior. Working memory is often used synonymously with short-term memory, ...

processing. The concept of functional disconnection developed still further when it was applied to the understanding of the nature of

autistic spectrum The autism spectrum, often referred to as just autism or in the context of a professional diagnosis autism spectrum disorder (ASD) or autism spectrum condition (ASC), is a neurodevelopmental condition (or conditions) characterized by difficulti ...

disorder. Geschwind and Levitt in 2007 suggested a model of the symptoms of

autism The autism spectrum, often referred to as just autism or in the context of a professional diagnosis autism spectrum disorder (ASD) or autism spectrum condition (ASC), is a neurodevelopmental condition (or conditions) characterized by difficulti ...

in which higher-order association areas of the brain (that normally connect to the

frontal lobe The frontal lobe is the largest of the four major lobes of the brain in mammals, and is located at the front of each cerebral hemisphere (in front of the parietal lobe and the temporal lobe). It is parted from the parietal lobe by a groove b ...

) are partially disconnected during development, thereby explaining the heterogeneity of

etiology. The autism group at Cambridge University provided evidence that the functional connectivity of medial

temporal lobe The temporal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain. The temporal lobe is involved in proc ...

structures specifically is abnormal in people with Asperger’s syndrome, at least during fearful face processing. Melillo and Leisman have similarly concluded that a functional disconnection syndrome is a basis for explaining the symptoms of autistic spectrum disorder.

References

{{DEFAULTSORT:Functional Disconnection Pseudoscience