Functional disconnection
Encyclopedia
Functional Disconnection in contradistinction to physical disconnection of the cerebral hemispheres by surgical resection
, trauma
or lesion
, is a concept first described by Leisman. and Sroka, Solsi, and Bornstein , to describe disintegrated function in the brain in the absence of anatomical damage. Applications have included alexia
without agraphia dyslexia
, persistent vegetative state
and minimally conscious state
as well as autistic spectrum disorders .
Sandra Witelson reported in 1977 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's processing of its own specialized functions and result in deficient linguistic, sequential cognitive processing and in overuse of the spatial, holistic cognitive 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 resulting from a cerebrovascular accident 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, somesthetic, auditory
, and visual system
s), so that pathways other than the one impaired by the brain lesion are used.
Friston in 1998 presented a mechanistic account of how dysfunctional integration among neuronal systems arises, based on the central role played by synaptic plasticity
in shaping the connections. They hypothesized that the pathophysiology of schizophrenia
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 post-natal 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
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
functional disconnection, particularly prefrontal dissociation and abnormal prefrontal-parietal
interaction during working memory
processing.
The concept of functional disconnection developed still further when it was applied to the understanding of the nature of autistic spectrum disorder. Geschwind and Levitt in 2007 suggested a model of the symptoms of autism
in which higher-order association areas of the brain that normally connect to the frontal lobe
are partially disconnected during development explaining the heterogeneity of autism
etiology. The autism group at Cambridge University provided evidence that the functional connectivity of medial temporal lobe
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,
Resection
Resection may refer to:*Segmental resection , the partial removal of an organ or other body structure*Resection , a means of establishing a location...
, trauma
Trauma (medicine)
Trauma refers to "a body wound or shock produced by sudden physical injury, as from violence or accident." It can also be described as "a physical wound or injury, such as a fracture or blow." Major trauma can result in secondary complications such as circulatory shock, respiratory failure and death...
or lesion
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
, is a concept first described by Leisman. and Sroka, Solsi, and Bornstein , to describe disintegrated function in the brain in the absence of anatomical damage. Applications have included alexia
Alexia
Alexia may refer to:People*Alexia *Alexia *Alexia Bryn, a Norwegian pair skater*Alexia Dechaume-Balleret, a French professional tennis player...
without agraphia dyslexia
Dyslexia
Dyslexia is a very broad term defining a learning disability that impairs a person's fluency or comprehension accuracy in being able to read, and which can manifest itself as a difficulty with phonological awareness, phonological decoding, orthographic coding, auditory short-term memory, or rapid...
, persistent vegetative state
Persistent vegetative state
A persistent vegetative state is a disorder of consciousness in which patients with severe brain damage are in a state of partial arousal rather than true awareness. It is a diagnosis of some uncertainty in that it deals with a syndrome. After four weeks in a vegetative state , the patient is...
and minimally conscious state
Minimally conscious state
Minimally Conscious State 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 relatively new category of disorders of consciousness. The...
as well as autistic spectrum disorders .
Sandra Witelson reported in 1977 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's processing of its own specialized functions and result in deficient linguistic, sequential cognitive processing and in overuse of the spatial, holistic cognitive 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 resulting from a cerebrovascular accident resulting in pure alexia
Alexia
Alexia may refer to:People*Alexia *Alexia *Alexia Bryn, a Norwegian pair skater*Alexia Dechaume-Balleret, a French professional tennis player...
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, somesthetic, auditory
Auditory system
The auditory system is the sensory system for the sense of hearing.- Outer ear :The folds of cartilage surrounding the ear canal are called the pinna...
, and visual system
Visual system
The visual system is the part of the central nervous system which enables organisms to process visual detail, as well as enabling several non-image forming photoresponse functions. It interprets information from visible light to build a representation of the surrounding world...
s), so that pathways other than the one impaired by the brain lesion are used.
Friston in 1998 presented a mechanistic account of how dysfunctional integration among neuronal systems arises, based on the central role played by synaptic plasticity
Synaptic plasticity
In neuroscience, synaptic plasticity is the ability of the connection, or synapse, between two neurons to change in strength in response to either use or disuse of transmission over synaptic pathways. Plastic change also results from the alteration of the number of receptors located on a synapse...
in shaping the connections. They hypothesized that the pathophysiology of schizophrenia
Schizophrenia
Schizophrenia is a mental disorder characterized by a disintegration of thought processes and of emotional responsiveness. It most commonly manifests itself as auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social...
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 post-natal 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
Learning
Learning is acquiring new or modifying existing knowledge, behaviors, skills, values, or preferences and may involve synthesizing different types of information. The ability to learn is possessed by humans, animals and some machines. Progress over time tends to follow learning curves.Human learning...
. The pathophysiology results in a disruption of the reinforcement of adaptive behavior
Adaptive behavior
Adaptive behavior is a type of behavior that is used to adjust to another type of behavior or situation. This is often characterized by a kind of behavior that allows an individual to change an unconstructive or disruptive behavior to something more constructive. These behaviors are most often...
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
Parietal lobe
The parietal lobe is a part of the Brain positioned above the occipital lobe and behind the frontal lobe.The parietal lobe integrates sensory information from different modalities, particularly determining spatial sense and navigation. For example, it comprises somatosensory cortex and the...
functional disconnection, particularly prefrontal dissociation and abnormal prefrontal-parietal
Parietal
Parietal may refer to:*Parietal placentation*Parietal lobe of the brain*Parietal bone of the skull*Parietal scales of a snake lie in the general region of the parietal bone*Parietal cell in the stomach*Parietal pleura...
interaction during working memory
Working memory
Working memory has been defined as the system which actively holds information in the mind to do verbal and nonverbal tasks such as reasoning and comprehension, and to make it available for further information processing...
processing.
The concept of functional disconnection developed still further when it was applied to the understanding of the nature of autistic spectrum disorder. Geschwind and Levitt in 2007 suggested a model of the symptoms of autism
Autism
Autism is a disorder of neural development characterized by impaired social interaction and communication, and by restricted and repetitive behavior. These signs all begin before a child is three years old. Autism affects information processing in the brain by altering how nerve cells and their...
in which higher-order association areas of the brain that normally connect to the frontal lobe
Frontal lobe
The frontal lobe is an area in the brain of humans and other mammals, located at the front of each cerebral hemisphere and positioned anterior to the parietal lobe and superior and anterior to the temporal lobes...
are partially disconnected during development explaining the heterogeneity of autism
Autism
Autism is a disorder of neural development characterized by impaired social interaction and communication, and by restricted and repetitive behavior. These signs all begin before a child is three years old. Autism affects information processing in the brain by altering how nerve cells and their...
etiology. The autism group at Cambridge University provided evidence that the functional connectivity of medial temporal lobe
Temporal lobe
The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....
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,