Central nervous system

1. Universitatea “L. Blaga din Sibiu Facultatea de Ştiinţe Specializarea Psihologie FUNDAMENTELE PSIHOLOGIEILateralizarea cerebralăseminar 7 Asist. univ. drd. Elena BOULEANU Sibiu, 2009

2. Aphasia and Apraxia:The Dominant Left Hemisphere Broca’s area that is associated with grammar and speech production 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 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

3. Tests of Cerebral Lateralization 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 PET of FMRI techniques have revealed that there is typically more activity in the left hemisphere than the right during language-related activities

4. Tests of Cerebral Lateralization Many studies have reported a relation between speech laterality and handedness; the following general conclusions have been reached: Nearly all (about 95%) right-handed subjects are left-hemisphere dominant for speech; most left-handed or ambidextrous subjects (about 70%) are also left-hemisphere dominant for speech; and Early left-hemisphere damage can cause the right hemisphere to become dominant for speech and the left hand to be preferred

5. Tests of Cerebral Lateralization 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 It was designed to reveal the function of the brain’s largest commissure, the corpus callosum

6. Differences BetweenThe Left and Right Hemispheres Language is the most lateralized of all abilities; the left-hemisphere is better than the right at most language-related tasks however, the right hemisphere proved to be able to understand single written and spoken words; also right-hemisphere detects prosody and discourse The right hemisphere proved better than the left at a variety of tasks involving spatial ability, emotional stimuli and musical tasks

7. Differences BetweenThe Left and Right Hemispheres 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) This is usually termed analytical (LH) versus holistic (RH)

8. Three Theories ofCerebral Asymmetry Analytic-synthetic theory Motor theory Linguistic theory

9. Analytic-Synthetic Theory 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 LH (pieces of the whole) operates in logical, sequential, analytic fashion RH (the whole) makes immediate, overall synthetic judgments

10. Motor Theory Posits that LH is specialized for fine motor movement of which speech is but one example Two lines of evidence: Lesions of the LH disrupt facial movements more than do RH lesions, even when they are not related to speech Degree of disruption of nonverbal facial movements is positively correlated with the degree of aphasia

11. Linguistic Theory 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 (or is this just showing ASL is a language, and that language is highly analytical?)

12. Broca’s Area Inferior left prefrontal lobe in left hemisphere Damage leads to deficits primarily speech production (problems with expression) and also grammatical comprehension Wernicke’s Area Left temporal lobe, just posterior to the primary auditory cortex Damage leads to deficits to semantic language comprehension (problems with reception) and speech is imcomprehensible, despite having correct grammar, rhythm an intonation (word salad)

13. Aphasia Broca– limbajularticulat http://www.youtube.com/watch?v=f2IiMEbMnPM Wernicke– înţelegerea limbajului oral http://www.youtube.com/watch?v=aVhYN7NTIKU&feature=related

14. Dislexia (Alexia ) Damage to the left angular gyrus (area of left temporal and parietal cortex jost posterior to Wernicke’s) Inability to read despite intact language comprehension and production

15. Disgraphia (Agraphia) Also due to damage to the left angular gyrus Inability to write despite intact language comprehension and production Involvement of LAG in alexia and agraphia show its responsible for language related visual input

16. Sex differences and Lateralization Some evidence suggests that the male brain is more lateralized than female brain. Some fMRI studies show that females tend to use both hemispheres in language-related tasks more so than males.

17. Sex differences and Lateralization No documented gender disparity in overall intelligence Male advantage on spatial tasks Female advantage on language and memory tasks Disproportionate male incidence of dyslexia, delayed speech, attention disorders and mental retardation

18. Brainsize Modern study of brain size (Nopoulos et al., 2000) Male and female brains similar No significant differences in volumes of cerebrospinal fluid, volume of the cerebellum, cortical depth, gyral and sulcal shape, and degree of cortical surface complexity Males have larger cerebrum

19. Functional Organization Brain Lateralization Theory “Left-brain” females and “right-brain” males? Theory does not work – females should be superior at math Bilateral language processing theory – Damage to specific hemisphere has distinct effects on men, but not women (Springer & Deutsch, 1981) Women use both hemispheres to process language, men more lateralized to left (Shaywitz et al., 1995) Research inconclusive Other studies show same amount of lateralization (Frost et al., 1999) Meta-analysis: no significant differences (Sommer, Aleman, Bouma, & Kahn, 2004)

20. Functional Organization Brain matter – MRI study (Haier, Jung, Yeo, Head, & Alkire, 2005) Women have more white matter and less gray matter than men in regions associated with intelligence Similar IQ scores, but brain functions in different ways Men – frontal and parietal lobes Women – frontal lobe and Broca’s area Allows for differences in IQ subtests, but similar overall IQ Women’s brains more efficient?

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