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PSYC 207
Michael Souza

Cerebral Asymmetry 11/7/2012 6:00:00 PM -1 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 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) *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 Behavioral Asymmetry in the Brain 11/7/2012 6:00:00 PM Behavioral Asymmetry in the Intact Brain -Not guaranteed that a region once controlled disrupted function -The hemisphere may execute instructions required for specific function Asymmetry in the Visual System -RIGHT visual field = travel to left visual cortex -LEFT visual field = project to right visual cortex *Tachistoscope: visual info presented to each visual field independently -Compare accuracy w/ which info from visual fields is processed – infer which hemisphere is best suited to processing different types of info *Information presented to only one visual field = processed more efficiently by specialized hemisphere to receive it -Left: words Right: faces/visuospatial stimuli Asymmetry in the Auditory System -B
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