Cerebral Lateralization

Hemispheres of the Brain

Our brain is divided into two main hemispheres, the left and the right. Each hemisphere is dominant in certain functions. Click either the left or the right hemisphere of the brain below and fill in the hemisphere’s appropriate functions. 

LEFT HEMISPHERE                            RIGHT HEMISPHERE

LEFT HEMISPHERE: Vision: words and letters, Audition: language sounds, Touch: NA, Movement: complex movement and ipsilateral movement, Memory: verbal memory and findings of meanings in memories, Language: speech, reading, writing, and arithmetic, Spatial Ability: NA

RIGHT HEMISPHERE: Vision: faces, geometric patterns, and emotional expression, Audition: non-language sounds and music, Touch: tactile patterns and Braille, Movement: movement in spinal patterns, Memory: nonverbal memory and perceptual aspects of memories, Language: emotional content, Spatial Ability: Mental rotation of shapes, geometry, direction, and distance

·         Sodium Amytal

     The sodium amytal test of language lateralization is normally administrated to patients before neurosurgery (Pinel, 2011). Neurosurgeons prepare and plan for surgery after the results are ready from each patient’s sodium amytal test. The results are important to avoid damaging any areas of the cortex; likely to be involved in language (Pinel, 2011). When this test takes places the carotid arteries, one at a time on both sides of one’s neck are the sites where a small amount of sodium amytal is injected (Pinel, 2011). Pinel, (2011), “the injection anesthetizes the hemisphere on that side for a few minutes, thus allowing the capacities of the other hemisphere to be assessed” (p. 413). While this test is administered twice separately, patients are asked to recite a different series of phrases such as days of the week and to name pictures of common objects (Pinel, 2011). Once the hemisphere normally the left hemisphere, which is specialized for speech is anesthetized, the patient is rendered completely mute for a minute or two and once the ability to talk returns, there are errors of serial order and naming (Pinel, 2011).

·         Dichotic Listening

     The dichotic listening test is administered to healthy patients because it is noninvasive (Pinel, 2011). During the standard test three pairs of spoken digits are presented through earphones; the digits of each pair are presented simultaneously, one to each ear (Pinel, 2011). This is where a patient will hear digits like 1, 4, and 6 in one ear while hearing 7, 9, and 10 in the other ear; afterward the patient is asked to recite all digits that were heard. Kimura found that most people report slightly more of the digits presented to the right ear than the left, which is indicative of left-hemisphere specialization for language; although patients identified by the sodium amytal test as having right-hemisphere specialization for language performed better with the left ear than the right (Pinel, 2011). Although sounds from each ear are projected to both hemispheres, Kimura believed that contralateral connections are stronger and take precedence when two different sounds are simultaneously competing for access to the same cortical auditory centers (p. 414).

         ·            Functional Brain Imaging

     The use of functional brain-imaging is how lateralization of function is studied. One’s activity in the brain is monitored by positron emission tomography (PET) or functional magnetic resonance imaging (fMRI) while activities are achieved such as reading (Pinel, 2011). Functional brain-imaging techniques show that there is significantly more activity in the left hemisphere than in the right hemisphere through the use of language tests (Pinel, 2011).   

·         Comparing effects of unilateral lesions

     Lesions in the left-hemisphere are more likely than lesions in the right-hemisphere lesions to produce ipsilateral motor problems; although the effects of unilateral brain lesions indicates that the right hemisphere is superior to the left as far as performance on some tests of emotion (Pinel, 2011).  

Reference

Pinel, J. P. J. (2011). Biopsychology (8th ed.). Boston, MA: Pearson.