1
Q
disconnection
A
the cutting or resetting cerebral connection
2
Q
Disconnection syndrome
A
the ensuing behavioral effects of disconnection
3
Q
Intact Monkey - anatomically intact
A
- hemispheres connected by commissures including…
- optic chiasm - where two hemiretinas intersect
- corpus callosum - bundle of fibers that interconnect the two hemispheres
4
Q
tame monkey
A
commissures disconnected, left amygdala removed
- If the objects were presented to the eye ipsilateral to the hemisphere with the ablated amygdala, the animal appeared tame even if the objects were typically frightening to monkeys.
- when the right eye is covered, and the left amygdala removed, visual info is unavailable to motor system
5
Q
wild monkey
A
commissures disconnected, left amygdala removed
- If the objects were presented to the eye ipsilateral to the intact amygdala, the animal made its usual specie’s typical responses to threats and appeared wild.
- left eye covered, the circuit in the right hemi for activating species typical behavior is intact.
6
Q
disconnection monkey experiment results
+ steps
A
- for an animal to display species’s typical responses to a visual stimulus, information must project from the eye to the visual cortex, passing through the temporal lobes to the amygdala and from the amygdala then to the brain stem and frontal cortex
- these connections activate respectively the autonomic responses, movements and facial expressions.
- If that hemisphere contains an intact amygdala, the circuit for activating specie’s typical behavior is complete and behavior would be typical.
- If the amygdala in the hemisphere is not intact, visual information will be disconnected from modal systems and can not elicit specie’s typical behavior.
7
Q
three major types of neural fiber pathways connecting to neocortex:
A
- association pathways
- projection pathways
- commissural pathways
8
Q
association pathways
A
- made of long fiber bundles that connect distant neocortical areas
- short, subcortical, U-shaped fibers that connect adjacent neocortical areas
9
Q
projection pathways
A
- include ascending fibers from lower brain centers up to the neocortex
- ex: projections from the thalamus, and descending fibers from neocortex to brainstem and spinal cord
10
Q
commissural pathways
A
- connect the two hemispheres
- include principally: corpus callosum, anterior commissure, and hippocampal commissures
- among areas that do receive interhemispheric connections, the density of projections is not homogeneous
- Cortical areas that represent the body’s midline, including the central meridian of the visual field, auditory fields, and the track of the body on the somatosensory and motor cortex, have the densest connections
11
Q
commissural connection in primary visual cortex (V1)
A
- no interhemispheric connections, except for that part representing the midline of the visual world (visual meridian)
- V1 represents the visual world topographically, and there is no need for one half of the representation to be connected to the other
12
Q
commissural connections in motor and sensory areas
A
- motor and sensory areas for distal parts of the limbs, mainly hands and feet, lack commissural connections
- bc essential function is to work independently of one another, it could be argued that the connections are not necessary
13
Q
callosal connections (3)
A
- most callosal projections connect to homotopic areas, presumably to meet the two areas together functionally
- projection zones within a hemisphere also connect to homotopic zones in the contralateral hemisphere
- ex: area V1 is connected to area V2, not only within a hemisphere, but also across hemispheres, because area V1 in one hemisphere also sends connection to area V2 in the opposite hemisphere
- a group of projections has a diffuse terminal distribution
- possibly to alert appropriate zone in one hemisphere that the other is active
14
Q
homotopic areas
A
identical points in the two cerebral hemispheres that are related to the body’s midline
15
Q
A
16
Q
genu
A
- anterior part of corpus callosum
- contains the fibers projecting from the prefrontal cortex
- Fibers through the body of the corpus callosum, proceeding from front to the back, project from the premotor, motor, somatosensory, and posterior parietal cortices
17
Q
splenium
A
Fibers in the posterior callosum, or splenium, project from the superior temporal, inferior temporal, and visual cortices.
18
Q
anterior commissure
A
much smaller than the corpus callosum and connects parts of the anterior temporal lobe, amygdala, and the paralimbic cortex of the temporal lobe surrounding the amygdala
19
Q
humans born without corpus callosum
anterior commissure
A
the anterior commissure is greatly enlarged to connect far greater regions of the neocortex
20
Q
connectome studies
goals
A
- demonstrate that large scale neural networks underlie complex cognitive operations
- seek to unravel neural network architecture and how networks relate to cerebral functions
21
Q
Diffusion Tensor Imaging and DTI tractography
A
they can be mathematically described as comprising sets of nodes, neuronal elements and edges
22
Q
graph theory
A
- nodes (neuronal elements) interconnect with related nodes and clustering to functional modules
- Individual modules maintain mutual nodal connections, but form few connections called hubs, to other modules
- Mathematical analysis have identified a specific and especially densely connected set of hub regions that require disproportionately high metabolic activity and are believed to factor in efficient communication and functional integration across the brain.
23
Q
connector hub
A
nodes that connect with connector hubs in other modules
24
Q
provincial hub
A
nodes that connect primarily to similar nodes in the same module
25
connectivity of cortical hubs in human brain
* Each hub participates in several dynamic brain networks as defined by fMRI and Magnetoencephalography recordings, MEG recordings including the default and salience networks
* Cortical hubs emerged relatively early in brain development but continue to increase their functional interactions into adolescence.
26
importance of severed connections as an underlying factor in the effects of cerebral damage
Hugo Liepmann
If a patient was given a verbal command to use the left hand in a particular way
some apraxias might result from disconnections
* If a patient was given a verbal command to use the left hand in a particular way, only the verbal left hemisphere will understand the command
* implies that to move the left hand, a signal will then have to travel from the left hemisphere through the corpus callosum to the right hemispheric region that controls movement of the left hand
* interrupting the part of the corpus callosum that carries the command from the left hemisphere to the right will disconnect the right hemisphere's motor region from the command
* apraxia will occur in the absence of the weakness or incoordination of the left hand
* will develop in the presence of a lesion of the right hemisphere motor cortex, which controls the actual movement of the left hand.
27
Behavioral effects of severing corpus callosum in cats
(Myers and Sperry)
* if sensory information was allowed separate access to each hemisphere, each hemisphere could be shown to have its own independent perceptual, learning, and memory processes
* corpus callosum is important
28
why disconnection of neocortex is easy
1. the primary sensory areas have no direct connections among one another
2. even in higher-order sensory zones, only few direct connections exist among sensory systems
3. the hemispheres are in large part symmetrical and are connected by only a few projection systems
29
hemispheres may become completely separated under three conditions:
1. cut as therapy for epilepsy - commissurotomy
2. callosal agenisis
3. animal research
* disconnections are performed to trace functional systems, to model human symptoms, and to answer basic questions about interhemispheric development
30
commissurotomy
recovery
* surgical several of cerebral commissures
* elective treatment for intractable epilepsy
* when medication is ineffective
* each hemisphere retains fibers that allow it to see only the opposite side of the visual world
* each hemisphere predominantly receives information from the opposite side of the body and controls movement on the opposite side of the body
* isolates speech in persons with lateralized speech
* the dominant hemisphere, usually the left, is able to speak, and the non-dominant hemisphere is not
* "typical" behavior recovers within two years despite independent functioning of hemispheres
31
split brain patients
* their scores on standardized tests are normal
* patient's everyday behavior appears similar to that of typical unified people
32
specific tests on split brain patients
* specific tests, such as those Sperry and his coworkers obtain with their split-brain patients in 1974, can still show differences between the functioning of split-brain patients and that of people with intact cerebral connections
* usual testing procedures include presenting stimuli only to one hemisphere and then testing each hemisphere for what transpired
* ex: split-brain patient who is asked to touch an out-of-view object with one hand, and then find a similar object with the other hand, is unable to match the objects
* each hemisphere can be shown to have its own sensations, percepts, thoughts, and memories, that are not accessible to the other hemisphere
33
callosal agenesis
impairments
congenitally reduced or absent interhemispheric connections
* can perform inter hemispheric comparisons of visual and tactile info
* patients have enhanced conduction in the remaining commissure (ex: vision)
* developed enhanced ability to use their few uncrossed projections (ex: tactile info)
* impaired general intelligence, expressive and receptive language, visual and spatial reasoning, memory, motor skills, etc
34
sensory disconnection
olfaction
connections are not crossed
* input from left nostril goes straight back into left hemi, same with right
* fibers travel through the anterior commissure join the olfactory regions in each hemisphere
35
sensory disconnnection - olfaction
case
* case: patient whose anterior commissure is severed - cannot name odors presented to the right nostril because the speaking left hemisphere is disconnected from the information
* rt hemi has the info but no control of speech
* olfactory function still intact but because the patient can use the left hand to pick out an object such as an orange that corresponds to the odor, smell
* no connection with speech is necessary because the right hemisphere both contains the olfactory information and controls the left hand
* if requested to use the right hand the patient will be unable to pick out the object because the left hemisphere which controls the right hand is disconnected
36
sensory disconnection
vision
information flashed to one visual field travels selectively to the contralateral hemisphere
* verbal material including words is perceived more accurately when presented to the right visual field
* prob bc the input travels to left "speaking" hemi
* visual spacial input such as a map produces a left visual field superiority because the right hemisphere appears to be superior to the left in analyzing spacial information
* visual field superiority observe the neuro-typical controls is relative
* visuospatial input - left field superiority
* relative effects occur because either hemisphere potentially has access to input to the opposite hemisphere through the corpus callosum which connects the visual area
37
sensory disconnection
vision
words presented to the left visual field
words presented to the left visual field and hence in right hemisphere are sometimes perceived, although not as accurately or consistently as when presented to the right visual field
38
sensory disconnection
vision
words presented to right visual field
verbal material perceived more accurately when presented to rt visual field, bc the input travels to the left, speaking hemisphere
39
if obj presented to left visual field
commissurotomy patient
* commissurotomy pt unable to read it or answer qs about it verbally (but right visual field no difficulties)
* commissurotomy pt will be unable to name it and will appear agnosic and aphasic
40
if obj presented to right visual field
commissurotomy pt
commissurotomy pt
obj will be correctly named
41
sensory disconnection
vision
split brain
the split brain pt is aphasic, alexic, and agnosic if verbal material or an obj requiring verbal response to presented visually only to rt hemi, but intact if material is presented to left hemi
42
sensory disconntection
somatosensory functions
* if the two hemispheres are disconnected the somatosensory functions of the left and right parts of the body become independent
* ex: if some object is placed in the left hand of a blindfolded callosal patient who is then asked to choose the presented object from an array of objects the left hand can pick out the object but the right hand cannot
* if an object is placed in a blindfolded patient's right hand the patient can name it but cannot do so if the object is placed in the left hand because the sensory input is disconnected from the left speech hemisphere
* one hand has no way of knowing what the other hand is doing inn the absence of input coming from opposite hemisphere
43
normally
if object placed in left hand
if person is blind folded and right hand is molded into particular shape
* if obj placed in lt hand - can be named because tactile info projects to right hemi, crosses to left, and has access to speech zones
* if a person is blindfolded an rt hand is molded to form a particular shape, the left hand is able to copy the shape
44
sensory disconnection
audition
both crossed and uncrossed connections
* words played in left ear can travel directly to the left hemisphere or can go to the right hemisphere and then to the left through the corpus callosum
* bilateral anatomical arrangement appears to reduce the effects of these connections
45
dichotic listening task
* input from the left ear is thoroughly suppressed
* patient reports only those words played to the right ear
* digits or words played to the right ear are reported but no input to the left ear is reported
* surprising because words played to the left ear even under these conditions will be expected to attain some direct access to the left hemisphere. But this direct access does not appear to exist when the hemispheres are disconnected.
46
partial disconnection
Posterior part of corpus callosum is intact
* combine markedly milder effects than those of complete commissurotomy with the same therapeutic benefits
* patients with partial disconnection are significantly better at motor tasks
47
partial disconnection
splenium
subserves visual transfer
48
partial disconnection
region just in front of splenium
affects somatosensory transfer
49
The term “disconnection syndrome” is used to describe the behavioral effects of ...
a. the disruption of communication between the brainstem and cerebrum
b. psychiatric disorders characterized by out-of-body experiences
c. the destruction of one or more cortical regions contributing to a neural network
d. an interruption of communication between two cerebral regions
d. an interruption of communication between two cerebral regions
50
The MOST posterior portion of the corpus callosum is called the...
splenium
51
Commissurotomy is performed in humans primarily as a treatment for ...
epilepsy
52
The condition that results from severing the anterior commissure is called \_\_\_\_\_\_\_.
anosmia
53
The only sensory system whose afferent fibers do NOT cross is ...
olfactory system
54
Functionally, the visual system is entirely crossed, such that stimuli in the left-visual field are initially processed by the right-visual cortical areas and vice versa. Which of the following systems is MOST similar to vision in this regard?
somatosensory
55
On which of the following tasks would you expect to see the LEAST impairment following hemispheric disconnection?
a. tactile apperception
b. chimeric face perception
c. puzzle assembly
d. dichotic listening
d. dichotic listening
56
\_\_\_\_\_ is the name of the aphasic syndrome that is the result of a disconnection between the anterior and posterior speech zones.
conduction aphasia
57
anosomic
lacking sense of smell
58
conduction aphasia
speech sounds and movements are retained, but speech is impaired because it cannot be conducted form one region to the other
59
the cutting or resetting cerebral connection
disconnection
60
the ensuing behavioral effects of disconnection
Disconnection syndrome
61
* hemispheres connected by commissures including...
* optic chiasm - where two hemiretinas intersect
* corpus callosum - bundle of fibers that interconnect the two hemispheres
Intact Monkey - anatomically intact
62
commissures disconnected, left amygdala removed
* If the objects were presented to the eye ipsilateral to the hemisphere with the ablated amygdala, the animal appeared tame even if the objects were typically frightening to monkeys.
* when the right eye is covered, and the left amygdala removed, visual info is unavailable to motor system
tame monkey
63
commissures disconnected, left amygdala removed
* If the objects were presented to the eye ipsilateral to the intact amygdala, the animal made its usual specie's typical responses to threats and appeared wild.
* left eye covered, the circuit in the right hemi for activating species typical behavior is intact.
wild monkey
64
1. association pathways
2. projection pathways
3. commissural pathways
three major types of neural fiber pathways connecting to neocortex:
65
1. made of long fiber bundles that connect distant neocortical areas
2. short, subcortical, U-shaped fibers that connect adjacent neocortical areas
association pathways
66
* include ascending fibers from lower brain centers up to the neocortex
* ex: projections from the thalamus, and descending fibers from neocortex to brainstem and spinal cord
projection pathways
67
* connect the two hemispheres
* include principally: corpus callosum, anterior commissure, and hippocampal commissures
* among areas that do receive interhemispheric connections, the density of projections is not homogeneous
* Cortical areas that represent the body's midline, including the central meridian of the visual field, auditory fields, and the track of the body on the somatosensory and motor cortex, have the densest connections
commissural pathways
68
* no interhemispheric connections, except for that part representing the midline of the visual world (visual meridian)
* V1 represents the visual world topographically, and there is no need for one half of the representation to be connected to the other
commissural connection in primary visual cortex (V1)
69
* motor and sensory areas for distal parts of the limbs, mainly hands and feet, lack commissural connections
* bc essential function is to work independently of one another, it could be argued that the connections are not necessary
commissural connections in motor and sensory areas
70
1. most callosal projections connect to homotopic areas, presumably to meet the two areas together functionally
2. projection zones within a hemisphere also connect to homotopic zones in the contralateral hemisphere
* ex: area V1 is connected to area V2, not only within a hemisphere, but also across hemispheres, because area V1 in one hemisphere also sends connection to area V2 in the opposite hemisphere
3. a group of projections has a diffuse terminal distribution
* possibly to alert appropriate zone in one hemisphere that the other is active
callosal connections
71
identical points in the two cerebral hemispheres that are related to the body's midline
homotopic areas
72
* anterior part of corpus callosum
* contains the fibers projecting from the prefrontal cortex
* Fibers through the body of the corpus callosum, proceeding from front to the back, project from the premotor, motor, somatosensory, and posterior parietal cortices
genu
73
Fibers project from the superior temporal, inferior temporal, and visual cortices.
splenium
74
much smaller than the corpus callosum and connects parts of the anterior temporal lobe, amygdala, and the paralimbic cortex of the temporal lobe surrounding the amygdala
anterior commissure
75
the anterior commissure is greatly enlarged to connect far greater regions of the neocortex
humans born without corpus callosum
anterior commissure
76
1. demonstrate that large scale neural networks underlie complex cognitive operations
2. seek to unravel neural network architecture and how networks relate to cerebral functions
connectome studies
goals
77
they can be mathematically described as comprising sets of nodes, neuronal elements and edges
Diffusion Tensor Imaging and DTI tractography
78
* nodes (neuronal elements) interconnect with related nodes and clustering to functional modules
* Individual modules maintain mutual nodal connections, but form few connections called hubs, to other modules
* Mathematical analysis have identified a specific and especially densely connected set of hub regions that require disproportionately high metabolic activity and are believed to factor in efficient communication and functional integration across the brain.
graph theory
79
nodes that connect with connector hubs in other modules
connector hub
80
nodes that connect primarily to similar nodes in the same module
provincial hub
81
* Each hub participates in several dynamic brain networks as defined by fMRI and Magnetoencephalography recordings, MEG recordings including the default and salience networks
* Cortical hubs emerged relatively early in brain development but continue to increase their functional interactions into adolescence.
connectivity of cortical hubs in human brain
82
some apraxias might result from disconnections
* If a patient was given a verbal command to use the left hand in a particular way, only the verbal left hemisphere will understand the command
* implies that to move the left hand, a signal will then have to travel from the left hemisphere through the corpus callosum to the right hemispheric region that controls movement of the left hand
* interrupting the part of the corpus callosum that carries the command from the left hemisphere to the right will disconnect the right hemisphere's motor region from the command
* apraxia will occur in the absence of the weakness or incoordination of the left hand
* will develop in the presence of a lesion of the right hemisphere motor cortex, which controls the actual movement of the left hand.
importance of severed connections as an underlying factor in the effects of cerebral damage
Hugo Liepmann
83
* if sensory information was allowed separate access to each hemisphere, each hemisphere could be shown to have its own independent perceptual, learning, and memory processes
* corpus callosum is important
Behavioral effects of severing corpus callosum in cats
(Myers and Sperry)
84
1. the primary sensory areas have no direct connections among one another
2. even in higher-order sensory zones, only few direct connections exist among sensory systems
3. the hemispheres are in large part symmetrical and are connected by only a few projection systems
why disconnection of neocortex is easy
85
1. cut as therapy for epilepsy - commissurotomy
2. callosal agenisis
3. animal research
* disconnections are performed to trace functional systems, to model human symptoms, and to answer basic questions about interhemispheric development
hemispheres may become completely separated under three conditions:
86
* surgical several of cerebral commissures
* elective treatment for intractable epilepsy
* when medication is ineffective
* each hemisphere retains fibers that allow it to see only the opposite side of the visual world
* each hemisphere predominantly receives information from the opposite side of the body and controls movement on the opposite side of the body
* isolates speech in persons with lateralized speech
* the dominant hemisphere, usually the left, is able to speak, and the non-dominant hemisphere is not
* "typical" behavior recovers within two years despite independent functioning of hemispheres
commissurotomy
87
* their scores on standardized tests are normal
* patient's everyday behavior appears similar to that of typical unified people
split brain patients
88
* specific tests, such as those Sperry and his coworkers obtain with their split-brain patients in 1974, can still show differences between the functioning of split-brain patients and that of people with intact cerebral connections
* usual testing procedures include presenting stimuli only to one hemisphere and then testing each hemisphere for what transpired
* ex: split-brain patient who is asked to touch an out-of-view object with one hand, and then find a similar object with the other hand, is unable to match the objects
* each hemisphere can be shown to have its own sensations, percepts, thoughts, and memories, that are not accessible to the other hemisphere
specific tests on split brain patients
89
congenitally reduced or absent interhemispheric connections
* can perform inter hemispheric comparisons of visual and tactile info
* patients have enhanced conduction in the remaining commissure (ex: vision)
* developed enhanced ability to use their few uncrossed projections (ex: tactile info)
* impaired general intelligence, expressive and receptive language, visual and spatial reasoning, memory, motor skills, etc
callosal agenesis
90
connections are not crossed
* input from left goes straight back into left hemi, same with right
sensory disconnection
olfaction
91
* case: patient whose anterior commissure is severed - cannot name odors presented to the right nostril because the speaking left hemisphere is disconnected from the information
* rt hemi has the info but no control of speech
* olfactory function still intact but because the patient can use the left hand to pick out an object such as an orange that corresponds to the odor, smell
* no connection with speech is necessary because the right hemisphere both contains the olfactory information and controls the left hand
* if requested to use the right hand the patient will be unable to pick out the object because the left hemisphere which controls the right hand is disconnected
sensory disconnnection - olfaction
case
92
information flashed to one visual field travels selectively to the contralateral hemisphere
* verbal material including words is perceived more accurately when presented to the right visual field
* prob bc the input travels to left "speaking" hemi
* visual spacial input such as a map produces a left visual field superiority because the right hemisphere appears to be superior to the left in analyzing spacial information
* visual field superiority observe the neuro-typical controls is relative
* visuospatial input - left field superiority
* relative effects occur because either hemisphere potentially has access to input to the opposite hemisphere through the corpus callosum which connects the visual area
sensory disconnection
vision
93
words presented to the __ visual field are sometimes perceived, although not as accurately or consistently
sensory disconnection
vision
words presented to the left visual field
94
verbal material perceived more accurately when presented to ___ visual field, bc the input travels to the \_\_\_
sensory disconnection
vision
words presented to right visual field
right, left
95
* commissurotomy pt unable to read it or answer qs about it verbally (but right visual field no difficulties)
* commissurotomy pt will be unable to name it and will appear agnosic and aphasic
if obj presented to left visual field
commissurotomy patient
96
commissurotomy pt
obj will be correctly named
if obj presented to right visual field
commissurotomy pt
97
the split brain pt is aphasic, alexic, and agnosic if verbal material or an obj requiring verbal response to presented visually only to rt hemi, but intact if material is presented to left hemi
sensory disconnection
vision
split brain
98
* if the two hemispheres are disconnected the somatosensory functions of the left and right parts of the body become independent
* ex: if some object is placed in the left hand of a blindfolded callosal patient who is then asked to choose the presented object from an array of objects the left hand can pick out the object but the right hand cannot
* if an object is placed in a blindfolded patient's right hand the patient can name it but cannot do so if the object is placed in the left hand because the sensory input is disconnected from the left speech hemisphere
* one hand has no way of knowing what the other hand is doing inn the absence of input coming from opposite hemisphere
sensory disconntection
somatosensory functions
99
both crossed and uncrossed connections
* words played in left ear can travel directly to the left hemisphere or can go to the right hemisphere and then to the left through the corpus callosum
* bilateral anatomical arrangement appears to reduce the effects of these connections
sensory disconnection
audition
100
* input from the left ear is thoroughly suppressed
* patient reports only those words played to the right ear
* digits or words played to the right ear are reported but no input to the left ear is reported
* surprising because words played to the left ear even under these conditions will be expected to attain some direct access to the left hemisphere. But this direct access does not appear to exist when the hemispheres are disconnected.
dichotic listening task
101
patients are significantly better at motor tasks
partial disconnection
Posterior part of corpus callosum is intact
102
subserves visual transfer
partial disconnection
splenium
103
affects somatosensory transfer
partial disconnection
region just in front of splenium
104
lacking sense of smell
anosomic
105
speech sounds and movements are retained, but speech is impaired because it cannot be conducted form one region to the other
conduction aphasia
