PSY 2C 08: BRAIN, BODY AND
BEHAVIOUR
UNIT–I: BRAIN AND BEHAVIOUR
TOPIC: Introduction to Disconnection
Syndrome
, DISCONNECTION SYNDROME
Disconnection syndrome is a general term for a collection of neurological symptoms caused via lesions to
associational or commissural nerve fibres by damage to the white matter axons of communication pathways in
the cerebrum (not to be confused with the cerebellum), independent of any lesions to the cortex. The behavioural
effects of such disconnections are relatively predictable in adults. Disconnection syndromes usually reflect
circumstances where regions A and B still have their functional specializations except in domains that depend on
the interconnections between the two regions.
Callosal syndrome, or split-brain, is an example of a disconnection syndrome from damage to the corpus callosum
between the two hemispheres of the brain. Disconnection syndrome can also lead to aphasia, left-sided apraxia,
and tactile aphasia, among other symptoms. Other types of disconnection syndrome include conduction aphasia
(lesion of the association tract connecting Broca’s area and Wernicke’s), agnosia, apraxia, pure alexia, etc...
Anatomy of cerebral connections
Theodore Meynert, a neuroanatomist of the late 1800s, developed a detailed anatomy of white matter pathways.
He classified the white matter fibres that connect the neocortex into three important categories – projection fibres,
commissural fibres and association fibres. Projection fibres are the ascending and descending pathways to and
from the neocortex. Commissural fibres are responsible for connecting the two hemispheres while the association
fibres connect cortical regions within a hemisphere. These fibres make up the interhemispheric connections in the
cortex.
Callosal disconnection syndrome is characterized by left ideomotor apraxia and left-hand agraphia and/or tactile
anomia, and is relatively rare.
HEMISPHERIC DISCONNECTIONS SYSTEMS
Many studies have shown that disconnection syndromes such as aphasia, agnosia, apraxia, pure alexia and many
others are not caused by direct damage to functional neocortical regions. They can also be present on only one
side of the body which is why these are categorized as hemispheric disconnections. The cause for hemispheric
disconnection is if the interhemispheric fibres, as mentioned earlier, are cut or reduced.
An example is commissural disconnect in adults which usually results from surgical intervention, tumour, or
interruption of the blood supply to the corpus callosum or the immediately adjacent structures. Callosal
disconnection syndrome is characterized by left ideomotor apraxia and left-hand agraphia and/or tactile anomia,
and is relatively rare.
BEHAVIOUR
UNIT–I: BRAIN AND BEHAVIOUR
TOPIC: Introduction to Disconnection
Syndrome
, DISCONNECTION SYNDROME
Disconnection syndrome is a general term for a collection of neurological symptoms caused via lesions to
associational or commissural nerve fibres by damage to the white matter axons of communication pathways in
the cerebrum (not to be confused with the cerebellum), independent of any lesions to the cortex. The behavioural
effects of such disconnections are relatively predictable in adults. Disconnection syndromes usually reflect
circumstances where regions A and B still have their functional specializations except in domains that depend on
the interconnections between the two regions.
Callosal syndrome, or split-brain, is an example of a disconnection syndrome from damage to the corpus callosum
between the two hemispheres of the brain. Disconnection syndrome can also lead to aphasia, left-sided apraxia,
and tactile aphasia, among other symptoms. Other types of disconnection syndrome include conduction aphasia
(lesion of the association tract connecting Broca’s area and Wernicke’s), agnosia, apraxia, pure alexia, etc...
Anatomy of cerebral connections
Theodore Meynert, a neuroanatomist of the late 1800s, developed a detailed anatomy of white matter pathways.
He classified the white matter fibres that connect the neocortex into three important categories – projection fibres,
commissural fibres and association fibres. Projection fibres are the ascending and descending pathways to and
from the neocortex. Commissural fibres are responsible for connecting the two hemispheres while the association
fibres connect cortical regions within a hemisphere. These fibres make up the interhemispheric connections in the
cortex.
Callosal disconnection syndrome is characterized by left ideomotor apraxia and left-hand agraphia and/or tactile
anomia, and is relatively rare.
HEMISPHERIC DISCONNECTIONS SYSTEMS
Many studies have shown that disconnection syndromes such as aphasia, agnosia, apraxia, pure alexia and many
others are not caused by direct damage to functional neocortical regions. They can also be present on only one
side of the body which is why these are categorized as hemispheric disconnections. The cause for hemispheric
disconnection is if the interhemispheric fibres, as mentioned earlier, are cut or reduced.
An example is commissural disconnect in adults which usually results from surgical intervention, tumour, or
interruption of the blood supply to the corpus callosum or the immediately adjacent structures. Callosal
disconnection syndrome is characterized by left ideomotor apraxia and left-hand agraphia and/or tactile anomia,
and is relatively rare.
