Chapter 15 part 2 Flashcards
disconnection syndrome
when communication between the two hemispheres stop
- usually caused by a lesion in the corpus callosum
general causes of disconnection syndrome
- medical refractory generalized epilepsy
- surgical callosotomy
- developmental: agenesis of the corpus callosum
anterior commissure
another small pathway for communication
- connects the two temporal lobes
- primary function unclear, but possibly olfaction
consequences of disconnection of corpus callosum and anterior commissure
1) effects on language
- alexia: inability to read
- unilateral (left) agraphia: inability to write
2) effects on sensorimotor systems
- vision: visual defects and neglect
- audition: left ear extinction (neglect)
- motor movement: apraxia
- transforming tactile information into language: left tactile anomia
3) effects on olfaction (specifically anterior commussure)
alexia in disconnection syndrome
patients are able to talk, but unable to read material presented in the left hemifield
- occurs when the splenium of the corpus callosum is involved in the lesion since it allows or transmission of the visual image to the left (language) angular gyrus
disconnection syndrome effects on language if only corpus callosum (splenim) is damaged
- alexia
- hemialexia: when the word is presented in the left visual field, the patient cannot say the word, but may be able to describe it (partial split)
- if the split is complete, then the patient has complete alexia and even a left side neglect
alexia without agraphia versus left hand agraphia
agraphia, particularly in the left hand, occurs with more anterior corpus callosum lesions
disconnection syndrome effects on visuospatial - sensorimotor
only the right hemisphere is able to perceive visuospatial information (e.g., seeing a cube); sees depth
so if there is a callosal disconnection, problem is manifested in the right hand if the patient is asked to draw a shape, instead of writing words
disconnection syndrome effects on audition - sensorimotor
most of the hearing is received via the contralateral (right cortex), and then the sounds need to be relayed back to the left cortex for comprehension
so if there is a callosal disconnection, sounds are not relayed back to the left hemisphere for comprehension
- show left ear extinction when sounds are presented simultaneously to both ears
- words/digits presented to right ear are reporting and those to left ear are not
- words presented to left ear should have direct access to left (language) hemisphere
disconnection syndrome effects on motor apraxia - sensorimotor
motor movement: unilateral (left) ideomotor apraxia
in response to verbal commands, patients are unable to carry out with the left hand some behavior that is readily carried out with the right hand; verbal command is adequately received by the left (language) hemisphere, but because of the corpus callosum disconnection, cannot reach the right hemisphere, which controls left hand movement
disconnection syndrome effects on transforming tactile information into language - sensorimotor
language = left hemisphere
put object in left hand, sensory information gets to right hemisphere
ask patient with split brain to name that object: cannot name it
put the same object in right hand: the patient can name it
disconnection syndrome effects on olfaction
anterior commissure disconnection specifically
in the normal condition, olfactory input to the right nostril travels directly back into the right hemisphere and crosses the anterior commissure, thus gaining access to the left (language)
- anosmia results when information is blocked and the left hemisphere has no way of knowing what odor the right hemisphere perceived
agenesis corpus callosum
- born without a corpus callosum
- midline gene deficit
- severe developmental disturbances
- patients exhibit reduced lateralization of brain functions
- language processing is often distributed across both hemispheres
presentation of agenesis corpus callosum in children
- vision impairments
- low muscle tone (hypotonia)
- poor motor coordination
- delays in motor milestones (e.g., sitting and walking)
- reduced perception of pain
- delayed toilet training
- chewing and swallowing difficulties
symptoms may sometimes be mistaken for Asperger’s syndrome
presentation of agenesis corpus callosum in adults
- seizures
- spasticity
- early feeding difficulties and/or gastric reflux
- hearing impairments
- abnormal head and facial features
- cognitive impairments or developmental disabilities
