PSYC 207 Chapter Notes -Visual System, Auditory System, Medical Ultrasound

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Published on 15 Apr 2013
School
UBC
Department
Psychology
Course
PSYC 207
Professor
Cerebral Asymmetry 11/7/2012 6:00:00 PM
-1st established by studying patients w/ disease lateralized to 1 hemisphere
-Owe current knowledge about localization & lateralized to study subjects
Patients with lateralized lesions
-Inferred functions from behavioral deficits from strokes/TBI
-Unilateral lesions in LEFT hemisphere (right handed patients) = aphasia
(Don’t occur from lesions in RIGHT hemisphere [left=language])
-2 hemispheres are lateralized/dissociated/function differently
-Double Dissociation by Hans-Leukas Teuber
•Prove that lesions to one side don’t disturb the other
Patients with Commissurotomy:
-Surgical procedure of corpus callosum to disconnect hemispheres
-Initially too variable, subsequently abandoned until 60’s
-Bogen & Vogel: section corpus callosum & smaller anterior commissure
-medically beneficial (seizure free) but had unique syndromes
Figure 11.4:Effect of Commissurotomy on Connections Between the
Hemispheres (normal function of brain)
1. Corpus callosum & connections severed no longer communicate
2. 2 hemispheres independent
(each receives sensory input from all sensory systems & control muscles)
3. Cortical connections w/ sensory/motor systems & body receptors
unaffected
4. SPLIT BRAIN : isolated, other hemisphere don’t have access to info
Figure 11.5: Information from visual field only sent to one hemisphere
-Visual pathways are crossed, visual fields (not eyes) represented in each
hemisphere, visual world (from both eyes) project to only ONE hemisphere
-Joined by corpus callosum connections
-Left visual fields of both eyes project to right visual cortex
-Both right fields project to left visual cortex
Figure 11.6: What does commisurotomy do?
1. Objects presented in left visual field travels to right hemisphere first
2. Visual input transferred from left visual field to right visual cortex
(via corpus callosum)
3. Corpus callosum transfers to left hemisphere
*PREVENTS TRANSFER
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Left hemisphere of SBP: initiate communication
Right: unable, lacks access to speech in left hem.
Conclusion: GRAPHIC APHASIA
•Image projected to right visual field, subject verbally identifies
•Image projected to left visual field, subject can’t see
*Right hemisphere = facial recognition
Brain Stimulation
-Penfield: surgical treatment of epilepsy by cortical lobotomy
Figure 11.9: Localizing Speech & Movement Areas of the Brain
(A) Patient comfortably lying, left hemisphere exposed, stimulate w/ EEG
(B) Identify critical cortical areas
-Left hemisphere stimulation = inability to speak
-Right hemisphere stimulation = inability to move
1. (EXCITATORY) Produce localized movement, dysthesia
(numbess/tingling), light flash, buzzing sensation
*Primary motor, somatosensory, visual, auditory areas/pathways
*Stimulation of either hemisphere w/ same frequency
2. (EXCITATORY) “Interpretive” & “Experiential” responses
*alterations of patient’s surroundings (déjà vu, fear, dreamy states,
reproduction of visual/auditory experiences upon stimulation
*Tissue showing epileptogenic discharge reveals asymmetry
*More common w/ RIGHT stimulation perceptual functions
3. (EXCITATORY) Accelerate speech production
*Left frontal/temporal region stimulation
*”Alerting” response (may occur in other cognitive processes-memory)
4. (INHIBITORY) Complex functions
-Language & memory, only when current applied while patient actively
engaged in specific behaviors
-LEFT = speech disruption
-RIGHT = behavior disruption (line orientation, facial expressions,
short-term memory for faces) RIGHT TEMPOPARIETAL CORTEX
Carotid Sodium Amobarbital Injection
*Language = left hemisphere for most people (except right-handed people)
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*Inject sodium amobarbital into CAROTID artery
-brief period of anesthesia of ipsilateral hemisphere
Figure 11.10: The Wada Test
*Advantage: study one hemisphere @ a time to determine speech control
LEFT CAROTID ARTERY INJECTION:
-left hemisphere briefly anesthetized
-Speech arrest/aphasic return
-Can’t move right arm
-No right visual field
RIGHT CAROTID ARTERY INJECTION:
-Sensory & motor symptoms on LEFT
-No speech disturbance (unless it is dominant for speech, right-handed)
*Not necessarily limited to one hemisphere, asymmetrical
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Document Summary

1st established by studying patients w/ disease lateralized to 1 hemisphere. Owe current knowledge about localization & lateralized to study subjects. Unilateral lesions in left hemisphere (right handed patients) = aphasia (don"t occur from lesions in right hemisphere [left=language]) Double dissociation by hans-leukas teuber: prove that lesions to one side don"t disturb the other. Surgical procedure of corpus callosum to disconnect hemispheres. Bogen & vogel: section corpus callosum & smaller anterior commissure. Medically beneficial (seizure free) but had unique syndromes. Figure 11. 4:effect of commissurotomy on connections between the. Figure 11. 5: information from visual field only sent to one hemisphere. Visual pathways are crossed, visual fields (not eyes) represented in each hemisphere, visual world (from both eyes) project to only one hemisphere. Left visual fields of both eyes project to right visual cortex. Both right fields project to left visual cortex.

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