Chapter 17 - Study Guide: Connections

Question 1

What is a disconnection syndrome

Answer 1

results from cutting of cerebral connections

Question 2

Outline Downer’s experiment

Answer 2

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

Question 3

What are the 3 types of cerebral connections

Answer 3

1. association pathway
2. projection pathways
3. commissural pathways

Question 4

What are the two types of association pathways

Answer 4

1. long fiber bundles that connect distant regions
2. short, subcortical, u-shaped fibers connecting adjacent areas

Question 5

What does commissural pathways include

Answer 5

corpus callosum, anterior commissure, and hippocampal commissures

Question 6

What is Liepmann’s theory of apraxia

Answer 6

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

Question 7

What is agenesis of the corpus callosum?

Answer 7

born without a corpus callosum

Question 8

What are the symptoms of agenesis of the corpus callosum

Answer 8

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

Question 9

Give an example of a disconnection syndrome in vision

Answer 9

visual agnosia - inability to recognize objects although vision is normal (can describe object but not name it)

Question 10

Give an example of a disconnection syndrome in audition

Answer 10

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

Question 11

Give an example of a disconnection syndrome in touch

Answer 11

Tactile agnosia
blindfolded with object in L - can feel it but not name it
in R - object can be named

Question 12

Give an example of a disconnection syndrome in olfaction

Answer 12

ansomic - loss/absence of smell
the only system not crossed
ansomic if damage to reaching LH for speech

Question 13

Describe how alexia could be a disconnection syndrome

Answer 13

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

Question 14

Describe how agnosia could be a disconnection syndrome

Answer 14

disconnection between perceiving sensory information (primary sensory areas) and recognizing and interpreting information (association areas)

Question 15

What are cortical networks

Answer 15

cortical networks demonstrate the large-scale neural networks that underlie complex cognitive operations

Question 16

What are hubs

Answer 16

central nodes within cortical networks that play the role of facilitating and controlling flow of information between different brain regions

Question 17

What is the rich-club phenomenon

Answer 17

some hubs are densely connected and link modules together more extensively and further away

Question 18

How are cortical networks and hubs identified

Answer 18

1. using DTI (diffuser tensor imaging) to see the pathways
2. using MRI information to mathematically describe nodes and edges

Question 19

What is commissurotomy

Answer 19

surgery to cut or sever commissures that connect the two hemispheres
reduce seizure activity

Question 20

What are the 2 key principles in the development of networks

Answer 20

1. modularity (minimize long connections)
2. functional integration (still have rich-club hubs because must connect long distances)

Question 21

How are hubs and connectivity related to brain dysfunction such as dementia or psychiatric drugs

Answer 21

neurodegenerative disorders start in one module and slowly proceed along rich-club hubs

Question 22

what neurodegenerative disorders can be affected by hub connectivity

Answer 22

parkinsons, alzheimers, schizophrenia

Question 23

How can contralateral neglect be caused by a disconnection

Answer 23

= fails to attend to or respond to stimuli on one side of the body

both sides cannot effectively communicate or integrate information

Question 24

Where can contralateral neglect be caused by a disconnection

Answer 24

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

Question 25

What syndromes can be related to hyperconnectivity

Answer 25

synesthesia = increased connections between sensory regions
hallucinations = increased ventral stream connections
phobias = increased connections between visual stimuli and amygdala