1
Q
cerebral asymmetry
A
anatomical, physiological, or behavioral differences between the two cerebral hemispheres
2
Q
laterality
A
two cerebral hemispheres have separate functions
3
Q
challenges to studying cerebral asymmetry
A
- laterality is relative
- both hemispheres participate in nearly every behavior
- environmental and genetic influence on laterality
- cerebral organization of some left handers and females appears less asymmetrical than that of right-handers in males
- a range of animals with asymmetrical brains
- songbirds, rats, cats, and monkeys
4
Q
major anatomic differences between two hemispheres
A
identified with MRI
- rt hemi: slightly larger and heavier; lt hemi: contains more gray matter (neurons)
- temporal lobes: specialization
- left: language
- right: music functions
- temporal lobe & thalamus:
- anatomical asymmetry in the temporal lobe’s cortex correlates with an asymmetry in the thalamus
- structural asymmetry compliments apparent functional asymmetry of the thalamus
- left thalamus, like left hemi, also dominant for language functions
- frontal operculum (Broca’s area):
- organized differently on left and right hemisphere
- left side: area of cortex buried in the sulci is greater
- grammar production
- right side: area visible on surface is 1/3 larger
- tone of voice (prosody)
- lateralization of the functions
- lateral fissure: slope of lateral fissure is gentler on the left hemisphere than on the right
- tempororparietal cortex lying ventral to lateral fissure appears larger on the right
5
Q
neocortical asymmetry
describe
A
- overall neocortical surface area was the same in both hemispheres
- rt hemisphere: extends further anteriorly than the left
- lt hemisphere: extends farther posteriorly than the right
- overall pattern of asymmetry is evident across both hemispheres
6
Q
neocortical asymmetry
largest asymmetry favored
A
- left hemi: in Sylvian and medial temporal regions
- right hemi: in posterior parietal and dorsal lateral pre-frontal areas
7
Q
neocortical asymmetry
occipital horns of the lateral ventricles
A
5x likely to be longer on the right side than on the left
8
Q
neuronal asymmetries
A
- dendritic fields of pyramidal cells have abundant branches in Broca’s area (left frontal operculum)
- neurons in each region have a distinct pattern of the dendritic branching
- important bc: each branch is a potential location for enhancing or suppressing neuronal communication → more branch points = cells w more degrees of freedom w respect to function
9
Q
gene asymmetries
A
- human genome project
- genes expressed differently in the two hemispheres
- epigenetic changes mimic their relationship between genes
- experience may differentially influence the two hemispheres
10
Q
lateralized =
A
= dissociated
11
Q
double dissociation
A
- two neocortical areas are functionally dissociated by two behavioral tests
- performance on each test is affected by a lesion in one zone but not in the other
12
Q
hemisphere double dissociation ex
A
- left-hemi lesions: (rt-handed patients) produce deficits in language functions – speech, writing, and reading, that are not produced by right-hemisphere lesions
- → the two hemispheres’ functions are dissociated
- rt hemi lesions: performing spatial tasks, singing, playing musical instruments, and discriminating tonal patterns,
- Because a right-hemisphere lesion disturbs tasks that are not disrupted by left-hemisphere lesions and vice versa, the two hemispheres are doubly dissociated.
13
Q
case study: double dissociation
conclusion
A
- Subsequent to removal of the left temporal lobe, PG was impaired only on verbal tests
- Subsequent to removal of the right temporal lobe, SK was impaired only on nonverbal tests.
- Both patients performed normal on many tests providing evidence for localization as well as for lateralization of functions
14
Q
case study: double dissociation
PG
A
- patient A, PG
- 31 yo man, developed seizures in 6th year preceding neurosurgery, seizures poorly controlled by medication and subsequent neurological investigations revealed large tumor in anterior part of left temporal lobe
- preoperative tests: superior intelligence, significant deficits in verbal memory
- left temporal lobectomy
- decreased intelligence ratings
- further decreased verbal memory scores
15
Q
case study: double dissociation
SK
A
- patient B, SK
- preoperative scores: low score on recall of complex drawing
- right temporal lobectomy
- decreased intelligence ratings
- decreased nonverbal memory scores for simple and complex designs
16
Q
commissurotomy
A
- surgical disconnection of the two hemispheres by cutting the corpus callosum
- to prevent the spread of a seizure when meds fail
17
Q
epileptic seizures
A
may begin in a restricted region of one hemisphere and spread through the fibers of the corpus callosum, the commissure, to the homologous location in the opposite hemisphere
18
Q
after commissurotomy
A
split brain
- two hemisphere independent, can’t communicate
- each receives sensory input from all sensory system and each can control body’s muscle
- sensory info can be presented to one hemisphere, and its function can be studied without the other hemi having access
- right hemi: reasonably good recognition ability, but cannot initate speech (bc lacks access to speech mechanisms in left)
- have a physical key → they can grab it
19
Q
how vision is affected by split brain
A
- input from left visual field goes to right hemi
- input from right visual field goes to left hemi
20
Q
how speech is affected by split brain
A
21
Q
when left hemi of split brain pt has access to info
A
it can initiate speech and communicate about the info
22
Q
when right hemi of split brain pt has access to info
A
can recognize but cannot initiate speech
23
Q
split brain patients - faces
A
- unaware of the gross discordance between the pictures two sides
- right hemisphere plays special role in recognizing faces
24
Q
tachistoscope
A
- visual info can be presented to each visual field independently
- information presented to only one visual field is processed most efficiently by the hemisphere specialized to receive it
25
CSA injection
non speech hemi
may produce no speech arrest or only brief arrest
26
Stimulation CSA Injection
sodium amobarbital injection (wada test)
inject sodium amobarbital into carotid artery to produce brief period of anesthesia of ipsilateral hemisphere
* advantage: each hemi can be studied separately
* patients with anesthesia of either hemisphere are totally nonresponsive to visual stimulation to the contralateral visual field
* about 98% of right-handers and 70% of left-handers show speech disturbance after sodium amobarbital injection into the left hemisphere, but not after injection into the right hemisphere
27
CSA innjectionn
speech hemi
* results in unequivocal localization of speech bc injection into the speech hemi arrests speech for up to several minutes
* as speech returns, characterized by aphasic errors
28
brain stimulation
stimulation: to identify speech and movement areas and to localize the extent of a tumor or epileptogenic tissues
surgeon stimulates exposed cortex and records conscious patient's responses
29
stimulation of left hemi
can block the ability to speak
30
stimulation of right hemi
does not block ability to speak
31
behavioral asymmetries
a specific behavioral symptom associated with damage does not necessarily mean that the region controlled the disrupted function
32
visual system
behavioral asymmetries
present each hemisphere selectively with specific visual information - completely crossed
33
auditory system
behavioral asymmetries
* not completely as crossed as visual bc both hemis recieve projections from each ear
* crossed auditory connections are more numerous and more rapidly conducting than ispilateral projections
* left ear superiority
* perception of melodies
* left hemi
* specialized for processing language related sounds
* right hemi
* specialized for processing music related sounds
34
auditory system
left ear superiority
perception of melodies
35
auditory system
left hemi
specialized for processing language related sounds
36
auditory system
right hemi
specialized for processing music related sounds
37
dichotic listening tasks
* subjects recalled more digits that had been presented to the right ear than to the left
* → when different stimuli are presented simultaneously to each ear, the pathway from the right ear to the speaking hemisphere has preferred access (and ispilateral pathway from left ear is relatively suppressed
38
somatosensory system
behavioral asymmetries
what kind of tasks
* almost completely crossed → allows easy behavioral comparison
* left hand of rt handed participants is superior at nearly all tasks of recognizing shapes, angles, patterns
* blind and sighted participants read braille more rapidly with left hand
* spatial info for rt hemi
39
challenges of laterality studies
1. behavioral measures of laterality do not correlate perfectly with direct measures of cerebral asymmetry
2. strategies can alter performance significantly
3. participants' preconceived biases may affect performance
4. laterality effects may be a result of experience rather than biological factors
40
specialization theory
* unique functions for each hemisphere
* extreme unilateral specialization model
* only one hemisphere facilitates a given psychological process
* other models
* the two hemis might process info in distinctly different ways
41
interaction theory
1. cooperation between each hemi
2. hemispheres function simultaneously, but work on different aspects of the same processing
1. although the 2 hemis have the capacity to performa a given function, they may inhibit or suppress each other's activity
3. either the two hemis receive info preferentially and thus perform different analyses simultaneously or some mech enables each hemi to pay attention to specific types of info → leading to different hemispheric analysis
42
anatomical, physiological, or behavioral differences between the two cerebral hemispheres
cerebral asymmetry
43
two cerebral hemispheres have separate functions
laterality
44
1. laterality is relative
* both hemispheres participate in nearly every behavior
2. environmental and genetic influence on laterality
* cerebral organization of some left handers and females appears less asymmetrical than that of right-handers in males
3. a range of animals with asymmetrical brains
* songbirds, rats, cats, and monkeys
challenges to studying cerebral asymmetry
45
* although the overall neocortical surface area was the same in both hemispheres, an overall pattern of asymmetry exists throughout the brain
* rt hemisphere: extends further anteriorly than the left
* lt hemisphere: extends farther posteriorly than the right
neocortical asymmetry
46
* dendritic fields of pyramidal cells in Broca's area (left frontal operculum) with those in facial area of the motor cortexin the left precentral cortex compared to right:
* neurons in each region have a distinct pattern of the dendritic branching
* important bc: each branch is a potential location for enhancing or suppressing neuronal communication → more branch points = cells w more degrees of freedom w respect to function
neuronal asymmetries
47
* human genome project
* genes expressed differently in the two hemispheres
* epigenetic changes mimic their relationship between genes
* experience may differentially influence the two hemispheres
gene asymmetries
48
= dissociated
lateralized =
49
* two neocortical areas are functionally dissociated by two behavioral tests
* performance on each test is affected by a lesion in one zone but not in the other
double dissociation
50
* Subsequent to removal of the left temporal lobe, PG was impaired only on verbal tests
* Subsequent to removal of the right temporal lobe, SK was impaired only on nonverbal tests.
* Both patients performed normal on many tests providing evidence for localization as well as for lateralization of functions
case study: double dissociation
conclusion
51
* surgical disconnection of the two hemispheres by cutting the corpus callosum
* to prevent the spread of a seizure when meds fail
commissurotomy
52
may begin in a restricted region of one hemisphere and spread through the fibers of the corpus callosum, the commissure, to the homologous location in the opposite hemisphere
epileptic seizures
53
* two hemisphere independent, can't communicate
* each receives sensory input from all sensory system and each can control body's muscle
* sensory info can be presented to one hemisphere, and its function can be studied without the other hemi having access
* right hemi: reasonably good recognition ability, but cannot initate speech (bc lacks access to speech mechanisms in left)
* have a physical key → they can grab it
after commissurotomy
split brain
54
* input from left visual field goes to right hemi
* input from right visual field goes to left hemi
how vision is affected by split brain
55
how speech is affected by split brain
56
it can initiate speech and communicate about the info
when left hemi of split brain pt has access to info
57
can recognize but cannot initiate speech
when right hemi of split brain pt has access to info
58
* unaware of the gross discordance between the pictures two sides
* right hemisphere plays special role in recognizing faces
split brain patients - faces
59
* visual info can be presented to each visual field independently
* information presented to only one visual field is processed most efficiently by the hemisphere specialized to receive it
tachistoscope
60
* results in unequivocal localization of speech
* as speech returns, characterized by aphasic errors
* injection into non speech hemi - may produce no speech arrest or only brief arrest
* advantage: each hemi can be studied separately
* patients with anesthesia of either hemisphere are totally nonresponsive to visual stimulation to the contralateral visual field
* about 98% of right-handers and 70% of left-handers show speech disturbance after sodium amobarbital injection into the left hemisphere, but not after injection into the right hemisphere
Stimulation CSA Injection
sodium amobarbital injection (wada test)
61
stimulation: to identify speech and movement areas and to localize the extent of a tumor or epileptogenic tissues
surgeon stimulates exposed cortex and records conscious patient's responses
brain stimulation
62
can block the ability to speak
stimulation of left hemi
63
does not block ability to speak
stimulation of right hemi
64
* cannot speak, move right arm, see on the rt visual field
* patient cannot speak or later report on the experience
injecting CSA left carotid artery
anesthetizes left hemi
65
* sensory and motor symptoms on the left
* no speech disturbance unless the pts rt hemi is dominant for speech
injecting CSA right carotid hemi
66
a specific behavioral symptom associated with damage does not necessarily mean that the region controlled the disrupted function
behavioral asymmetries
67
present each hemisphere selectively with specific visual information - completely crossed
visual system
behavioral asymmetries
68
* not completely as crossed as visual bc both hemis recieve projections from each ear
* crossed auditory connections are more numerous and more rapidly conducting than ispilateral projections
* dichotic listening tasks
* subjects recalled more digits that had been presented to the right ear than to the left
* → when different stimuli are presented simultaneously to each ear, the pathway from the right ear to the speaking hemisphere has preferred access (and ispilateral pathway from left ear is relatively suppressed
* left ear superiority
* perception of melodies
* left hemi
* specialized for processing language related sounds
* right hemi
* specialized for processing music related sounds
auditory system
behavioral asymmetries
69
perception of melodies
auditory system
left ear superiority
70
specialized for processing language related sounds
auditory system
left hemi
71
specialized for processing music related sounds
auditory system
right hemi
72
* almost completely crossed → allows easy behavioral comparison
* left hand of rt handed participants is superior at nearly all tasks of recognizing shapes, angles, patterns
* blind and sighted participants read braille more rapidly with left hand
* spatial info for rt hemi
somatosensory system
behavioral asymmetries
73
1. behavioral measures of laterality do not correlate perfectly with direct measures of cerebral asymmetry
2. strategies can alter performance significantly
3. participants' preconceived biases may affect performance
4. laterality effects may be a result of experience rather than biological factors
challenges of laterality studies
74
* unique functions for each hemisphere
* extreme unilateral specialization model
* only one hemisphere facilitates a given psychological process
* other models
* the two hemis might process info in distinctly different ways
specialization theory
75
1. cooperation between each hemi
2. hemispheres function simultaneously, but work on different aspects of the same processing
1. although the 2 hemis have the capacity to performa a given function, they may inhibit or suppress each other's activity
3. either the two hemis receive info preferentially and thus perform different analyses simultaneously or some mech enables each hemi to pay attention to specific types of info → leading to different hemispheric analysis
interaction theory
76
5x likely to be longer on the right side than on the left
neocortical asymmetry
occipital horns of the lateral ventricles
77
* left hemi: in Sylvian and medial temporal regions
* right hemi: in posterior parietal and dorsal lateral pre-frontal areas
neocortical asymmetry
largest asymmetry favored
78
* results in unequivocal localization of speech bc injection into the speech hemi arrests speech for up to several minutes
* as speech returns, characterized by aphasic errors
CSA innjectionn
speech hemi
79
may produce no speech arrest or only brief arrest
CSA injection
non speech hemi
80
* subjects recalled more digits that had been presented to the right ear than to the left
* → when different stimuli are presented simultaneously to each ear, the pathway from the right ear to the speaking hemisphere has preferred access (and ispilateral pathway from left ear is relatively suppressed
dichotic listening tasks
81
X hemi lesions produce deficits in language functions,for example, speech, writing, and reading
left
82
X hemi lesions disrupt spatial tasks, singing, playing musical instruments, and discriminating tonal patterns
right
83
which hemi is larger and heavier?
rt hemi: slightly larger and heavier
84
which hemi contains more gray matter?
contains more gray matter (neurons)
85
structural asymmetry of lt and rt temporal lobes
lt: language
rt: music functions
86
left thalamus function
structural asymmetry compliments apparent functional asymmetry of the thalamus
left thalamus, like the left hemisphere, is also dominant for language functions
87
frontal operculum structural asymmetry
left vs right
(Broca's area)
organized differently on left and right hemisphere
* left side: area of cortex buried in the sulci is greater
* grammar production
* right side: area visible on surface is 1/3 larger
* tone of voice (prosody)
88
lateral fissure
structural asymmetry
* lateral fissure: slope of lateral fissure is gentler on the left hemisphere than on the right
* tempororparietal cortex lying ventral to lateral fissure appears larger on the right
