PSYC 479 - Ch. 11 - Cerebral Asymmetry PDF

Ch 11 – Cerebral asymmetry p. 262 – 265; 268 - 279  * Anatomical asymmetries in the human brain Laterality: the idea that the hemispheres have distinct functions (and structure) Left: producing and understanding language Right: per...

Ch 11 – Cerebral asymmetry p. 262 – 265; 268 - 279  * Anatomical asymmetries in the human brain Laterality: the idea that the hemispheres have distinct functions (and structure) Left: producing and understanding language Right: perceiving and synthesizing nonverbal information such as music and facial expression > spatial functions -  Variables to consider… 1. Laterality is relative not absolute 2. Cerebral site is at least as important in understanding brain function as cerebral side > - i e difflobes whin hemi diff that.... same lone blu hemi. 3. Environmental and genetic factors affect laterality > - left-handers & females have more symmetrical brains 4. A range of animals exhibit laterality 5. We act as though there is a single mind > left - hemisphere likely dominant interpreter Cerebral asymmetry IIIII ! larger temporal- larger in paretal lobe the left hemisphere (larger ↳Al ① ⑫  8 Major anatomical differences between hemispheres 1. Right hemisphere is slightly larger and heavier, but left has higher grey : white matter ratio Wernicke's larger ↑ 2. Structural asymmetry in temporal lobes (previous slide); likely corresponds to functional difference (left/language and right/music) ↳ Al larger 3. Thalamic asymmetry. Left dominance for language. > - thalamus has minor role in language (LH. larger 4. Steeper lateral fissure on right side 5. The frontal operculum (part of Broca’s area in left hemi) Left: larger area buried in sulci; grammar production Right: larger area visible on surface; possibly influences tone of voice (prosody)  Brudmann's area Wikimedia Commons , via S. Wise, CC BY 3.0 Fatemeh Geranmayeh, Sonia L. E. Brownsett, Richard J. > - Broid's L. hemisphere ↓ only functional structural / Broca's - open en frontal Chemisthere the insula Sebastian023, CC BY-SA 3.0 of cerebral part , via Wikimedia Commons cortex / of inferior S8 * Broca's area part · frontal frontal gyrus operculum ( part of Brocals area) = 6. Asymmetric distribution of A neurotransmitters in both cortical https://commons.wikimedia.org/w/index.php?curid=69773025 By Marc HE de Lussanet - Own work, CC0, and subcortical regions 7. Right hemisphere extends farther anteriorly, left hemisphere extends farther posteriorly. P Aka cerebral torque or. Rhander entral view Yakolevian torque > - more pronounced in Methodology – studying lateralization 1. Double dissociation 2. Commissurotomy patients 3. Carotid sodium amobarbital injection 4. Laterality studies in the intact brain 1. Double dissociation * provides strongest evidence for lateralization A Hans-Leukas Teuber (1955) An experimental technique by which 2 neocortical areas are functionally dissociated by two behavioural tests; performance on each test is affected by a lesion in one area, but not the other. > - functions are complimentary  Single Dissociation Lesion to structure A affects function X, but not Y > - localization of function Double Dissociation Patient 1: Lesion to A affects function X, but not Y Patient 2: Lesion to B affects function Y, but not X Hypothetical Reading Task Writing Task Neocortical Lesion Site A, Left Hemi Impaired Normal B, Left Hemi Normal Impaired single hemisphere provides evidence > - win of localization provide evidence of lateralization > equivalent structures - Hypothetical Language Task Spatial Task Neocortical Lesion Site A (Left Hemi) Impaired Normal B (Right Hemi) Normal Impaired 2. Commissurotomy (“split-brain”) patients ↳ all commissures have been severed just corpus callosum callostomy · = Cutting the 200 million nerve fibers of the corpus callosum First performed by William Van Wagnen in the early 1940s, soon abandoned ↳ variable outcomes ; split to prevent spread of epilepsy Resurgence in the 60s Research by Ron Myers and Roger Sperry in cats and monkeys (more in Ch 17) Joseph Brugen and Philip Vogel – severed cc and the smaller anterior commissure in about 2 dozen patients  Effect of commissurotomy on interhemispheric connections Sensory info can be presented to one hemisphere in isolation > sensation - & vision of opposite side is the wl access to stimuli only one Functions can then be studied without the other hemisphere having access to that information  Review: Geniculostriate System VI : striate cortex retina cells ↓ Cretinal ganglion optic nerve/tract ↓ lateral geniculate nucleus cranial nerve ↓ VI X - # to brain lpms) eye optic CONS) tract  I I Visual na tempora no temna nasal crosse , pathways retina chiasmt processed in contralateral hemisphere ⑭ Q ↑ tract that carries in fo from LGN to VI © 2023 Springer Nature Switzerland AG. Part of Springer Nature.  Visual info from one hemfiela right pathways left - hits ashemifield of an hemifield processed hitsan eye eye contralaterally in - 2 L ~ V V ~ L v the brain - L ~ L ~ ~ L L - v ~ - s X all info from left LVI RVI hemifield VI processed in right 12 vice versa)  Visual pathways the base at of the brain; not the corpus callosum  Corpus callosum is required to join both sides of the visual world X damage = in split brain patient ↳ refina + LON-VI RVI * Chemisphere ↑ ⑪ X corpus callusum verbal hemisphere > - Broca's area R. hemisphere is mute > - doesn'tproduce language Does the right hemisphere left hemifield perceive the spoon, even though it can’t speak? Patient N.G. > - able to pick up Spoonwl left hand , but can't describe object > - can't say what they saw de Haan, E. H. F., Corballis, P. M., Hillyard, S. A., Marzi, C. A., Seth, A., Lamme, V. A. F., Volz, L., Fabri, M., Schechter, E., Bayne, T., Corballis, M., & Pinto, Y. (2020). Split-Brain: What We Know Now and Why This is Important for Understanding Consciousness. Neuropsychology review, 30(2), 224–233. https://doi.org/10.1007/s11065-020-09439-3 The left hemisphere as the “interpreter” (Michael Gazzaniga, 1998) > makes more associations complex - > chose "ball" based on info - received from Rhemisphere ob all chosen b/ info the left hemisphere related to cow · right hemisphere (L hand , ( field) unable to process  Can the right hemisphere make non-verbal interpretations? Likely not. Split-brain subject presented with image pairs (e.g., matches, then wood) to each hemi separately R hand chose fire from a subsequent array of images L hand chose randomly from left Visual field to the left hand # i.e., The right hemisphere did not demonstrate ability to interpret the connection between image pairs The right hemisphere and facial recognition Jere Levy et al., (1972) – picka The chimeric figures test > - point > - pick a face ↑ would to face · point projected to left visual field  3. Carotid sodium amobarbital injection ↳i. e. Wada Test Jun Wada and Theodore Rasmussen (1960) Produces a brief period of anesthesia in the ipsilateral hemisphere - i e Lartery anesthesizes (hemisphere.. Today: injections made through catheter in femoral artery The Wada Test localizes speech to a particular hemisphere Injection into the speech hemisphere arrests speech for up to several minutes Advantages: Reversible Each hemisphere can be studied separately in the functional absence of the anesthetized one Can be used to study a variety of functions, including, memory and movement 4. Laterality studies in the intact brain Takes advantage of the crossed nature of our sensory systems to study the functions of one hemisphere over the other  Laterality studies in the visual system Tachistoscope Image flashed in one visual field for ~50ms Can investigate which hemisphere is best suited for processing specific types of info E.g., words processed more efficiently when presented to left hemi vs right E.g., faces and other visuospatial information show left visual field advantage ↳ R hemisphere The Auditory System ① ⑫ ① Man I inferior - ① auditory medulla > nerve > - - colliculus (ectum/ - ⑫MEN midbrain) * crosses at tectum ⑪  Laterality studies in the auditory system > - ipsilateral information suppressed when dichotic Early 1960s – Doreen Kimura: Dichotic listening task ↳ split brain patients report * info from one car travels to both hemisphere "Ga" * crossed connections more numerousrapid Neuropsychological test – RIGHT ear advantage > left hemisphere - Digits Words  Non-invasive task for Nonsense syllables identifying hemisphere dominant for language! Backward speech Morse code Difficult rhythms Ordering temporal information > - order in which References for each test information received found on p. 277 Neuropsychological test – LEFT ear advantage Melodies -right hemisphere Musical chords Environmental sounds Emotional sounds and hummed melodies Tones processed independently of linguistic content Complex pitch perception Neuropsychological test – NO ear advantage Vowels Isolated fricatives > - consonant soundul lots of airflow > - fff , SSS Rhythms Nonmelodic hums  Laterality studies in the somatosensory system Participants blindfolded; use each hand separately in various tasks Generally left hand is superior in spatial & - IDing shapes, angles, patterns R-hemisphere Both blind and sighted participants read braille more rapidly with left - hand ↓ of dots so spatial position , , right hemisphere  Laterality studies in the somatosensory system Dichaptic task – simultaneous presentation of a different tactile stimulus to each of the two hands Participants then look at objects and select those they previously touched E.g., letters or shapes made out of sandpaper Right hand advantage: letters Left hand advantage: shapes  Laterality studies in the motor system Left hemisphere lesions can produce apraxia – severe deficits in making or copying voluntary movement sequences ↑ complex Major confound: sensory/perceptual asymmetries exist, so the two sides do not start off equal Solutions: 1) Direct observation 2) Interference tasks  Laterality studies in the motor system 1. Direct observation Participants engaged in behaviour that doesn’t require a manual response left hemisphere dominance ↑ & language Kimura and Humphrys (1981): participants more likely to gesture with right hands when talking, equally likely to scratch themselves either hand Confound: hand preference vs functional asymmetry in motor control?  Laterality studies in the motor system 1. Direct observation Marilyn Wolf and Melvyn Goodale Sequence “mabopi” (1987) Single frame analysis of videotaped mouth movements produced when people make verbal vs nonverbal sounds left hemisphere dominance - for verbal non-verbal sounds Right side of mouth opens more quickly and widely  Laterality studies in the motor system 1. Direct observation Right hemisphere dominance: left side of face show emotions more strongly ↳ Rhemisphere dominance Wylie and Goodale (1988) showed that onset of facial expression occurs sooner on the left side of the face Thus, it’s not movement control itself which is asymmetrical, rather its function (i.e. movement for a purpose) ↳ is the purpose emotion ? verbal expression !  Laterality studies in the motor system 2. Interference tasks AKA multitasking Unpublished work by Hicks and Kinsbourne (1970s) Pianists learned to play different piece of music with each hand Were then asked to speak or hum while performing this task Speaking disrupted playing with right hand, humming disrupted playing with the left hand L nemi. R nemi. Confound: interference effects lessen with practice  Summary of data on cerebral lateralization Function Left Hemisphere Right Hemisphere Visual system Letters, words Complex geometric patterns, faces Auditory system Language-related sound Nonlanguage environmental sounds, music Somatosensory system Letters Braille, shapes Movement Complex voluntary Movements in spatial movement, verbal and patterns, facial expression nonverbal sound Memory Verbal memory Nonverbal memory Language Speech, reading, writing, arithmetic Spatial processes Geometry, sense of direction, mental rotation of shapes Top Hat