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Bryan Kolb & Ian Q. Whishaw’s. Fundamentals of Human Neuropsychology, Sixth Edition Chapter 12 Lecture PPT. Prepared by Gina Mollet, Adams State College . Variations in Cerebral Asymmetry. Portrait: Individual Responses to Injury. A.B. vs. L.P. A.B.
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Bryan Kolb & Ian Q. Whishaw’s Fundamentals of Human Neuropsychology, Sixth Edition Chapter 12 Lecture PPT Prepared by Gina Mollet, Adams State College
Portrait: Individual Responses to Injury • A.B. vs. L.P. • A.B. • Damage to the posterior part of the left temporal lobe • Difficulties in reading, speaking and remembering words • L.P. • Similar injury • Trouble recognizing faces, and drawing pictures • What could account for the differences?
Handedness and Functional Asymmetry About 10% of the population is left-handed Marion Annett
Anatomical Studies Hand preference correlated with differential asymmetry patterns Left-handers show more variation in asymmetry More fibers descend to the right hand MRI Little evidence of differences in anatomy in right and left-handers Greater hemispheric interaction in left-handers
Functional Cerebral Organization in Left-Handers Majority of left-handers have left lateralized speech Larger incidence of left-handedness among mentally defective children and children with neurological disorders Little known about cerebral organization of those with right hemisphere speech
Theories of Hand Preference: Environmental Theories Behavioral utility Proposes left hand is better for holding a shield or holding a baby, thus allowing the free right hand to perform skilled tasks Environmental Reinforcement Bias in the environment Environmental Accident Genetic bias towards right-handedness Left-handedness develops through a cerebral deficit
Snapshot: Genetic Influences on Brain Structure • Thompson and colleagues • Examined gray matter distribution in unrelated people and monozygotic and dizygotic twins • High similarity in monozygotic twins, but not in unrelated people
Theories of Hand Preference: Anatomical Theories Right-handedness Enhanced maturation and greater development of the left hemisphere Most species have a left-sided developmental advantage
Theories of Hand Preference: Hormonal Theories Geschwind and Galaburda Different levels of testosterone influence cerebral asymmetry Higher testosterone = increased likelihood of left-handedness
Theories of Hand Preference: Genetic Theories Annett Dominant gene rs+ for speech in the left hemisphere and right handedness Recessive gene rs- that results in no systematic bias for speech or handedness Model predicts about 12.5% left-handers
Sex Differences in Cerebral Organization Sex Differences in Behavior Motor Skills Men superior at throwing and intercepting objects Women superior at fine motor tasks Both present in young children
Sex Differences in Cerebral Organization Sex Differences in Behavior Spatial Analysis Men superior at mental rotation and in spatial navigation Women superior at spatial memory
Sex Differences in Cerebral Organization Sex Differences in Behavior Mathematical Aptitude Men superior at mathematical reasoning Women superior at computation Perception Women more sensitive to all sensory stimuli except vision Men superior at drawing mechanical objects
Sex Differences in Cerebral Organization Sex Differences in Behavior Verbal Ability Women superior verbal fluency and verbal memory Aggression Physical aggression more prevalent in men than women Genes or Experience? Effects are found in young children and adults Even after training women perform poorly on a water-level task
Sex Differences in Brain Structure Male brain larger than the female brain Females: larger volumes in areas associated with language, in medial paralimbic regions and some frontal lobe regions Men larger: Medial frontal and cingulate region Amygdala and hypothalamus Ventricles and overall white matter
Sex Differences in Brain Structure Differences in volume and organization in gray matter Influence of sex hormones Sex differences in the brain appear due to the distribution of estrogen and androgen receptors during development
Sex Differences in Brain Structure Established Asymmetries Larger left planum temporale found more often in men Men have larger asymmetry in the Sylvain fissure Planum parietale is about twice as large in men Women have more interhemispheric connections Women more likely to show an atypical fingerprint asymmetry
The Homosexual Brain Homosexual men outperform all groups on verbal fluency Homosexual women throw more accurately than heterosexual men
Research with Neurological Patients Degree of asymmetry in the lesion effects Differences in verbal IQ and performance IQ in men and women after left and right hemisphere damage Intrahemispheric Organization Differences in the appearance of aphasia and apraxia in men and women after left hemisphere damage
Explanations of Sex Differences: Hormonal Effects Organizing Effect Effects of hormones on brain organization Leads to sexual differentiation Assumed to take place during development
Explanations of Sex Differences: Hormonal Effects Functional effects of hormones seen in adulthood High estrogen associated with depressed spatial ability Estrogen affects levels of catecholamines and neuron structure Low testosterone associated with high spatial ability in men Hormone replacement in women increases verbal fluency and verbal and spatial memory
Explanations of Sex Differences Genetic Sex Linkage Recessive gene on the X chromosome accounts for spatial ability in girls Maturation Rate Brain matures faster in girls The slower the brain develops, the more asymmetry appears
Explanations of Sex Differences Environment Girls and boys are encouraged to engage in different activities leading to different abilities Not supported by a bulk of the evidence Preferred Cognitive Mode Women prefer to solve problems using a verbal strategy
Explanations of Sex Differences Conclusions Six significant behavioral differences appear between men and women Verbal ability Visuospatial analysis Mathematical ability Perception Motor skills Aggression
Environmental Effects on Asymmetry Culture and Language Asian languages might promote more right-hemisphere participation Reading pictorial Chinese produces right hemisphere activation not seen in reading English Exposure to multiple languages may influence cerebral organization of language
Sensory or Environmental Deficits Brain organization in nonhearing people Congenitally deaf subjects do not show a right visual field superiority for language tasks Deaf signers may acquire language in the left hemisphere, which may lead to development of visuospatial abilities in the left hemisphere
Sensory or Environmental Deficits Environmental Deprivation The case of Genie Rescued from an experiential deprivation and malnutrition at the age of 13 Developed cognitive abilities, but language lagged Found to be processing verbal and nonverbal stimuli in the right hemisphere Romanian orphanages Children had little environmental stimulation Long lasting damage to their brain development
Sensory or Environmental Deficits Epigenetics Changes in gene regulation that take place without changes in the DNA sequence Alterations in gene expression can influence cerebral function
Effects of Hemispherectomy Both hemispheres specialized at birth Removal of the right hemisphere Deficits on complex visuospatial deficits Removal of the left hemisphere Deficits in understanding spoken language Equipotentiality Equal potential for the hemispheres to perform any task Hemispherectomy provides evidence against equipotentiality
Ontogeny of Asymmetry Cerebral asymmetries are present before birth and become more pronounced in adulthood Left hemisphere shows a greater response to language at 1 week of age Parallel development theory At birth functional overlap between hemispheres Hemispheres becoming increasingly specialized for more complex tasks