FUNDAMENTELE PSIHOLOGIEILateralizarea cerebrală

seminar 7

Asist. univ. drd. Elena BOULEANUSibiu, 2009

Universitatea “L. Blaga din SibiuFacultatea de Ştiinţe

Specializarea Psihologie

Aphasia and Apraxia:The Dominant Left Hemisphere

Broca’s area that is associated with grammar and speech productionLiepmann 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 damageThis 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

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

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; andEarly left-hemisphere damage can cause the right hemisphere to become dominant for speech and the left hand to be preferred

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 hemispheresIt was designed to reveal the function of the brain’s largest commissure, the corpus callosum

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 discourseThe right hemisphere proved better than the left at a variety of tasks involving spatial ability, emotional stimuli and musical tasks

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)

Three Theories ofCerebral Asymmetry

Analytic-synthetic theoryMotor theoryLinguistic theory

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 differentLH (pieces of the whole) operates in logical, sequential, analytic fashionRH (the whole) makes immediate, overall synthetic judgments

Motor Theory

Posits that LH is specialized for fine motor movement of which speech is but one exampleTwo lines of evidence:

Lesions of the LH disrupt facial movements more than do RH lesions, even when they are not related to speechDegree of disruption of nonverbal facial movements is positively correlated with the degree of aphasia

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?)

Broca’s AreaInferior left prefrontal lobe in left hemisphereDamage leads to deficits primarily speech production (problems with expression) and also grammatical comprehension

Wernicke’s AreaLeft temporal lobe, just posterior to the primary auditory cortexDamage leads to deficits to semantic language comprehension (problems with reception) and speech is imcomprehensible, despite having correct grammar, rhythm an intonation (word salad)

Aphasia

Broca – limbajul articulat http://www.youtube.com/watch?v=f2IiMEbMnPMWernicke – înţelegerea limbajului oral http://www.youtube.com/watch?v=aVhYN7NTIKU&feature=related

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

Disgraphia (Agraphia)

Also due to damage to the left angular gyrus Inability to write despite intact language comprehension and productionInvolvement of LAG in alexia and agraphia show its responsible for language related visual input

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.

Sex differences and Lateralization

No documented gender disparity in overall intelligence

Male advantage on spatial tasksFemale advantage on language and memory tasksDisproportionate male incidence of dyslexia, delayed speech, attention disorders and mental retardation

Brain size

Modern study of brain size (Nopoulos et al., 2000)

Male and female brains similarNo 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

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)

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 intelligenceSimilar IQ scores, but brain functions in different ways

Men – frontal and parietal lobesWomen – frontal lobe and Broca’s areaAllows for differences in IQ subtests, but similar overall IQ

Women’s brains more efficient?

Dominanţa emisferică - Iluzia balerineihttp://www.argento.ro/depenet/iluzie-

optica/Dacă o vezi rotindu-se în sensul acelor de ceas, atunci foloseşti mai mult partea dreaptă a creierului, iar dacă o vezi în sens invers, partea stângă.

Unii pot să vadă balerina rotindu-se în ambele directii (cam 50% din cei testaţi).

Testarea dominanţei emisferice:http://psihologice.3x.ro/

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