PSY 215 Lecture 17 (3/28/2010) (Lateralization in the Brain) Dr. Achtman PSY 215

Transcription

1 PSY 215 Lecture 17 Topic: Lateralization in the Brain Chapter 14.1, pages Corrections: Lecture 16 (page 4) Broca s Area: trouble producing language, comprehension is okay. Announcements: Review for Exam 3 is Wednesday 3/30. Look over notes & come with questions. Exam 3 is on Monday 4/4 (learning, memory, attention, language, lateralization). Note: all images are taken from lecture notes unless otherwise specified Lecture Notes: Outline I. Syllabus Topics: Lateralization II. Why do right (R) and left (L) hemispheres process info differently? III. Visual System IV. How does information get to each hemisphere? V. Investigation Tools VI. Hemisphere Dominance Language / Vision / Development I. Syllabus Topics: Lateralization Lateralization Occurs: 1. Vision Occurs at the level of visual field and hemisphere - NOT at the level of eyeballs or retinas R visual field ends up in L hemisphere of brain / vice-versa 2. Movement R side is controlled by L hemisphere of brain / vice-versa 3. Somatasensation Touch on R leg is processed in L hemisphere / vice-versa 4. Attention Hemineglect: (primarily) R parietal cortex - R hemisphere damage = ignoring L side of world/space/object Written by:{noah Wagoner}, {nwagone4@mail.naz.edu} Page 1 of 7

2 5. Language Dominant in L hemisphere (96% of people have language in L hemi.) - 90% are R-handed (controlled by L hemi) - 10% are L-handed most have lang in L hemi some have lang in R hemi *some have lang split between both Wernicke s Area (comprehension) & Broca s Area (expression) are both in L hemi Lateralization does not occur: 1. Brain lateralized during development 2. Auditory Both ears help us localize sound localization happens at the level of ears (NOT at the level of the brain) 3. Learning 4. Memory II. Why do right (R) and left (L) hemispheres process info differently? 1. Somatasensory and motor systems are crossed ex) Stroke in R hemisphere = no movement on L side of body 2. Some functions are primarily in one hemisphere ex) Language = primarily in L hemisphere Anatomy of somatasensory and motor systems 1. Motor System/M 1 : [orange] anterior Most control over (most real estate ): - lips - jaw - hands - fingers 2. Somatasensory/ S 1 : [green] posterior Most control over (most real estate ): - hands - lips - mouth - tongue Written by:{noah Wagoner}, {nwagone4@mail.naz.edu} Page 2 of 7

3 III. Anatomy of Visual System R visual field [green] - projected on L half of each retina - ends in L hemi (Left V 1 ) L visual field [red] - projected on R half of each retina - ends in R hemi (Right V 1 ) Information gets to each hemisphere - some contralaterally (cross) - through optic chiasm - some ipsilaterally (same) ex) stare at finger in front of face close one eye images on both sides of finger are seen V 1 V 5 = less more complex - face recognition in V 5 (FFA) FFA: fusiform face area Visual Field A receptive field [dot] in one half of the visual field activates a neuron in the opposite hemisphere - Left dot = neuron activated in R hemi - Right dot = neuron activated in L hemi Travel from V1 to V5, receptive field becomes larger - combines info from previous area s neurons - Large dot = spills over into L visual field (and therefore R hemi) Written by:{noah Wagoner}, {nwagone4@mail.naz.edu} Page 3 of 7

4 IV. How does information get to each hemisphere? 1. Corpus Callosum (white matter) Main Highway Set of axons connecting the L & R hemis of brain Allows info to travel to each hemi 2. Anterior Commissure [blue] oval 3. Hippocampal Commissure [green] triangular Methods of transportation a. Homotopic [blue] (same location) - crosses from one area to same area in other hemi ex) Right S 1 Left S 1 b. Heterotopic [green] (different location) - crosses from one are to different area in other hemi ex) Right Occipital Left Temporal c. Ipsilateral [red] (same hemisphere) - moves to different structure in same hemi ex) Right Frontal Right Parietal Written by:{noah Wagoner}, {nwagone4@mail.naz.edu} Page 4 of 7

5 V. Investigation Tools 1. Sodium Amytal (Wada test) Put one hemisphere to sleep to examine capabilities of other hemisphere Only used when surgery is necessary to remove part of brain *risk of stroke (a) inject amytal (anesthetic) into L carotid artery (puts L hemi to sleep) - give patient spoon (b) ask patient what the object was unable to answer because language hemi is asleep (c) patient is able to use R hemi to imagine object and correctly identify a picture of it 2. fmri and Recording fmri: examine brain activity at certain point or during specific task recording: (epilepsy) used to find start of seizure 3. Surgery & Lesion Studies remove pieces of brain best outcome = young kids due to plasticity of brain ex) Patient H.M. bilateral surgery (medial parts of both temporal lobes) affected long term and declarative memory 4. Split Brain - corpus callosum is severed - prevents communication between the hemis - used when: several starting points of seizures uncontrollable through meds ex) image to right a. words (key ring) flashed on screen b. L visual field detected key R hemi R hemi controls left hand picks up key c. R visual field detected ring L hemi L hemi controls speech = says Ring Written by:{noah Wagoner}, {nwagone4@mail.naz.edu} Page 5 of 7

6 (a) normal brain full communication R hemi tells L hemi to say knight (a) partial split some communication R hemi sees word L hemi has to phish for word (b) complete split no communication R hemi sees word L hemi can t say it saw anything ex) Split Brain Video - Joe saw hammer - say hammer (triggered L hemi) - draw saw VI. Hemisphere Dominance 1. Language L hemi: comprehension (spoken, written) production (talking, writing) R hemi: recognize letters, words, and simple sentences (not complex sentences) emotional aspects of language (humor) music 2. Vision (image to right) L hemi: visual acuity apraxia local: small ex) small z s & squares R hemi: face processing (FFA) visuo-motor global: larger ex) large M & triangle 3. Development - If L hemi is damaged, R hemi can take over before 4 y/o - Corpus Callosum takes 5-10 years to mature *3 y/o are similar to split brain patients - People born without a C.C. are usually fine Written by:{noah Wagoner}, {nwagone4@mail.naz.edu} Page 6 of 7

7 For more information: Dr. V.S. Ramachandran humorously explains the case of split-brain patients with a Right Hemisphere that believes in God and the Left hemisphere that does not - followed by the question If this person dies what happens? Does one hemisphere go to heaven and the other go to hell? Documentary about 20-year old Tony Grombeier who was born without a corpus callosum. Brief description of what split brain is, the history of research, and shows Tony performs multiple experimental tasks as well as describing aspects of his everyday life. Brief news story of John Lawson Florer a 6-year old born with only half a brain. Real-life example: Knowing how different aspects of the brain are lateralized might be helpful in predicting brain damage based on a patient s observable physical characteristics. For example, a patient could have a limp right leg. From there you might be able to predict damage in the left hemisphere and further predict a language deficiency in the patient. Written by:{noah Wagoner}, {nwagone4@mail.naz.edu} Page 7 of 7