Chapter 17 - Study Guide: Connections Flashcards
What is a disconnection syndrome
results from cutting of cerebral connections
Outline Downer’s experiment
all commissures connecting two halves of the brain were cut and left amygdala was removed
right eye covered, left amygdala removed, visual information is unavailable to motor system
left eye covered, right amygdala intact, circuit for species-typical behaviour intact = wild monkey
What are the 3 types of cerebral connections
- association pathway
- projection pathways
- commissural pathways
What are the two types of association pathways
- long fiber bundles that connect distant regions
- short, subcortical, u-shaped fibers connecting adjacent areas
What does commissural pathways include
corpus callosum, anterior commissure, and hippocampal commissures
What is Liepmann’s theory of apraxia
proposed result of disconnection between motor areas in LH
given instruction to move left hand, signal must travel from L to RH which controls left hand movement
in apraxia, LH cannot inform RH so cannot move left hand
What is agenesis of the corpus callosum?
born without a corpus callosum
What are the symptoms of agenesis of the corpus callosum
can still perform interhemispheric comparisons of visual and tactile information due to connection of anterior commissure
deficits in language, IQ, visual and spatial reasoning, short and long term memory, slow intrahemispheric processing
Give an example of a disconnection syndrome in vision
visual agnosia - inability to recognize objects although vision is normal (can describe object but not name it)
Give an example of a disconnection syndrome in audition
auditory verbal agnosia
both uncrossed and crossed connections - words from left ear travel mostly to RH but also little to LH
direct access from left ear to LH does not appear when hemispheres are disconnected
Give an example of a disconnection syndrome in touch
Tactile agnosia
blindfolded with object in L - can feel it but not name it
in R - object can be named
Give an example of a disconnection syndrome in olfaction
ansomic - loss/absence of smell
the only system not crossed
ansomic if damage to reaching LH for speech
Describe how alexia could be a disconnection syndrome
alexia = recognize speech and writing, person cannot read
disruption in visual cortex and language centers
both areas are intact, but connection of corpus callosum disconnects the two
Describe how agnosia could be a disconnection syndrome
disconnection between perceiving sensory information (primary sensory areas) and recognizing and interpreting information (association areas)
What are cortical networks
cortical networks demonstrate the large-scale neural networks that underlie complex cognitive operations
What are hubs
central nodes within cortical networks that play the role of facilitating and controlling flow of information between different brain regions
What is the rich-club phenomenon
some hubs are densely connected and link modules together more extensively and further away
How are cortical networks and hubs identified
- using DTI (diffuser tensor imaging) to see the pathways
- using MRI information to mathematically describe nodes and edges
What is commissurotomy
surgery to cut or sever commissures that connect the two hemispheres
reduce seizure activity
What are the 2 key principles in the development of networks
- modularity (minimize long connections)
- functional integration (still have rich-club hubs because must connect long distances)
How are hubs and connectivity related to brain dysfunction such as dementia or psychiatric drugs
neurodegenerative disorders start in one module and slowly proceed along rich-club hubs
what neurodegenerative disorders can be affected by hub connectivity
parkinsons, alzheimers, schizophrenia
How can contralateral neglect be caused by a disconnection
= fails to attend to or respond to stimuli on one side of the body
both sides cannot effectively communicate or integrate information
Where can contralateral neglect be caused by a disconnection
Right parietal lobe = role in spatial awareness and attention
corpus callosum = communication
frontal lobe connections = disconnection between right parietal and frontal lobe impairs direct attention and responding to stimuli
