Cerebral lateralisation


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Cerebral lateralisation

  1. 1. Universitatea “L. Blaga din Sibiu<br />Facultatea de Ştiinţe<br />Specializarea Psihologie<br />FUNDAMENTELE PSIHOLOGIEILateralizarea cerebralăseminar 7<br />Asist. univ. drd. Elena BOULEANU<br />Sibiu, 2009<br />
  2. 2. Aphasia and Apraxia:The Dominant Left Hemisphere<br />Broca’s area that is associated with grammar and speech production<br />Liepmann discovered that apraxia(difficulty performing movements with either side of the body when asked to do so, but not when performing them spontaneously) was almost always associated with left-hemisphere damage<br />This led to the view that all complex activities were performed by the left hemisphere; the left and right hemispheres thus became known as dominant and minor hemispheres, respectively<br />
  3. 3. Tests of Cerebral Lateralization<br />The first evidence of language laterality came from comparisons of the effects of left and right unilateral lesions; today, the sodium amytal test and dichotic listening test are commonly used to assess language laterality<br />PET of FMRI techniques have revealed that there is typically more activity in the left hemisphere than the right during language-related activities<br />
  4. 4. Tests of Cerebral Lateralization<br />Many studies have reported a relation between speech laterality and handedness; the following general conclusions have been reached:<br />Nearly all (about 95%) right-handed subjects are left-hemisphere dominant for speech; <br />most left-handed or ambidextrous subjects (about 70%) are also left-hemisphere dominant for speech; and<br />Early left-hemisphere damage can cause the right hemisphere to become dominant for speech and the left hand to be preferred<br />
  5. 5. Tests of Cerebral Lateralization<br />In 1953, Myers and Sperry performed an experiment on cats that changed the way that we think about the brain; and it provided a means of comparing the function of the two hemispheres<br />It was designed to reveal the function of the brain’s largest commissure, the corpus callosum<br />
  6. 6. Differences BetweenThe Left and Right Hemispheres<br />Language is the most lateralized of all abilities; the left-hemisphere is better than the right at most language-related tasks<br /> however, the right hemisphere proved to be able to understand single written and spoken words; also right-hemisphere detects prosody and discourse<br />The right hemisphere proved better than the left at a variety of tasks involving spatial ability, emotional stimuli and musical tasks<br />
  7. 7. Differences BetweenThe Left and Right Hemispheres<br />The two hemispheres seem to engage different types of memory processing; LH attempts to place its experience in a larger context (relation of parts that make up the whole), while the RH attends strictly to the Gestalt perceptual characteristics of the stimulus (parts or whole but not relation between)<br />This is usually termed analytical (LH) versus holistic (RH)<br />
  8. 8. Three Theories ofCerebral Asymmetry<br />Analytic-synthetic theory<br />Motor theory<br />Linguistic theory<br />
  9. 9. Analytic-Synthetic Theory<br />Suggests that there are two fundamentally different modes of thinking, an analytic mode (LH) and synthetic mode (RH), and that the neural circuitry for each is fundamentally different<br />LH (pieces of the whole) operates in logical, sequential, analytic fashion<br />RH (the whole) makes immediate, overall synthetic judgments<br />
  10. 10. Motor Theory<br />Posits that LH is specialized for fine motor movement of which speech is but one example<br />Two lines of evidence:<br />Lesions of the LH disrupt facial movements more than do RH lesions, even when they are not related to speech<br />Degree of disruption of nonverbal facial movements is positively correlated with the degree of aphasia<br />
  11. 11. Linguistic Theory<br />Based on the view that the primary function of the LH is language; this is based on studies of deaf people who communicate using ASL; this ability is lost if these people suffer damage to the LH, even when they are able to make the movements required<br />(or is this just showing ASL is a language, and that language is highly analytical?)<br />
  12. 12. Broca’s Area<br />Inferior left prefrontal lobe in left hemisphere<br />Damage leads to deficits primarily speech production (problems with expression) and also grammatical comprehension<br />Wernicke’s Area<br />Left temporal lobe, just posterior to the primary auditory cortex<br />Damage leads to deficits to semantic language comprehension (problems with reception) and speech is imcomprehensible, despite having correct grammar, rhythm an intonation (word salad)<br />
  13. 13. Aphasia<br />Broca– limbajularticulat http://www.youtube.com/watch?v=f2IiMEbMnPM<br />Wernicke– înţelegerea limbajului oral http://www.youtube.com/watch?v=aVhYN7NTIKU&feature=related<br />
  14. 14. Dislexia (Alexia ) <br />Damage to the left angular gyrus (area of left temporal and parietal cortex jost posterior to Wernicke’s)<br />Inability to read despite intact language comprehension and production<br />
  15. 15. Disgraphia (Agraphia)<br />Also due to damage to the left angular gyrus<br />Inability to write despite intact language comprehension and production<br />Involvement of LAG in alexia and agraphia show its responsible for language related visual input<br />
  16. 16. Sex differences and Lateralization<br />Some evidence suggests that the male brain is more lateralized than female brain.<br />Some fMRI studies show that females tend to use both hemispheres in language-related tasks more so than males.<br />
  17. 17. Sex differences and Lateralization<br />No documented gender disparity in overall intelligence<br />Male advantage on spatial tasks<br />Female advantage on language and memory tasks<br />Disproportionate male incidence of dyslexia, delayed speech, attention disorders and mental retardation<br />
  18. 18. Brainsize<br />Modern study of brain size (Nopoulos et al., 2000)<br />Male and female brains similar<br />No significant differences in volumes of cerebrospinal fluid, volume of the cerebellum, cortical depth, gyral and sulcal shape, and degree of cortical surface complexity <br />Males have larger cerebrum<br />
  19. 19. Functional Organization<br />Brain Lateralization Theory<br />“Left-brain” females and “right-brain” males?<br />Theory does not work – females should be superior at math<br />Bilateral language processing theory – <br />Damage to specific hemisphere has distinct effects on men, but not women (Springer & Deutsch, 1981)<br />Women use both hemispheres to process language, men more lateralized to left (Shaywitz et al., 1995)<br />Research inconclusive<br />Other studies show same amount of lateralization (Frost et al., 1999)<br />Meta-analysis: no significant differences (Sommer, Aleman, Bouma, & Kahn, 2004)<br />
  20. 20. Functional Organization<br />Brain matter – MRI study (Haier, Jung, Yeo, Head, & Alkire, 2005)<br />Women have more white matter and less gray matter than men in regions associated with intelligence<br />Similar IQ scores, but brain functions in different ways<br />Men – frontal and parietal lobes<br />Women – frontal lobe and Broca’s area<br />Allows for differences in IQ subtests, but similar overall IQ<br />Women’s brains more efficient?<br />
  21. 21. Dominanţa emisferică - Iluzia balerinei<br />http://www.argento.ro/depenet/iluzie-optica/<br />Dacăo vezirotindu-se în sensulacelor de ceas, atuncifoloseştimaimultparteadreaptăa creierului, iardacăo veziîn sensinvers, parteastângă. <br />Uniipot săvadăbalerinarotindu-se în ambeledirectii (cam 50% din ceitestaţi).<br />Testarea dominanţei emisferice:<br />http://psihologice.3x.ro/Dominantacerebrala.html <br />