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Chapter 4

Chapter 4 booknotes

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University of Toronto Scarborough
Ted Petit

Chapter 4 Lateralization Laterality the functional specialization of the right and left hemispheres Early studies of the brail demonstrated that the left (LH0 is specialized for language and the control of the right and fingers. Although the functions of the right hemisphere (RH) were not readily understood. Hughlings Jackson suggested that it played a role in visual identification of objects. The RH is specialized for music, emotion and spatial abilities as well as control of the left hand fingers. The poor linguistic ability of the RH , tends to make it difficult to obtain information regarding its function . Neurologically normal brain function relies on constant communication between RH and LH. RH interrupts the sound waves that composed the emotional tone of speech (Prosody ) MODULE ; 4.1 SPLIT BRAIN When the corpus callosum was severed , the information that is received from the right visual cortex can no longer is integrated with that of the right visual cortex . Severing the corpus callosum results in a brain that is split into two separate halves that can no longer communicate with each other . In the 1960s , they began to perform complete commissutomies (cutting the corpus callosum and all of the other forebrain commissures on individuals with intractable epilepsy . Vogal and Bogen observed that complete commissurotomy was a successful treatment and that the frequency and severity of seizures were reduced. Motor , visual , auditory and somatosensory abilities of each hemisphere are intact . RH was capable of comprehending spoken and written words RH played a special role in the reorganization of faces . Intracarotd Ambarbital testing Intracarotid amorbarbital testing (IAT) is also known as the Walda test , reflecting the role of the neurosurgeon Juhn wada , who pioneered its use in the late 1940s . www.notesolution.com IAT is commonly used to asses the laterality of language in individuals who will be under surgery . Sodium amobarbitual is injected to the right or left internal carotid artery. Patients hands in the air, when anathesied the contralateral hand drops . The neuropsychologist then asses the cognitive functions of the individual. The goal of IAT is to asses language and memory capabilities of the two hemispheres independently . Anesthesia tends to last for a period of minutes , during which the cognitive functions of the unanaesthesized hemisphere can be examined. Studies using IAT have revealed that most individuals exhibit LH dominance for speech , although some individuals exhibit either bilateral or RH dominance for language . Bilateral representation does not mean that language is dispersed evenly , rather some type of interference with different language functions. IAT is very invasive Visual System The visual system sends information from receptors located in the retina of both eyes to both hemispheres. Visual information that is presented in the left side of space (left visual field ) is transmitted to the primary visual cortex of the RH from the nasal hemiretina of the left eye ( the half of the retina that is closest to your nose ) and the temporal hemirtina of the right eye (the half of the retina that is closest to the temples . Important to remember that the division of information between the hemiretinas occurs in the periphery of the retina . The foeva (center of the retina is used for fine detail and color vision ) automatically transmits information to both the right and left visual cortex. To allow the fovea to observe the stimulus the participant stares at a point at the center of the screen while keeping the stimulus away from the center of the visual field. Auditory System The auditory system is not as segregated as the visual system , as all receptors in the cochlea send projections bilaterally . www.notesolution.com
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