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Chapter 3&12

PSYB65 Chapter 3 & 12.docx

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University of Toronto Scarborough
Zachariah Campbell

PSYB65H3 LEC60 Chapter 3: Organization of the Nervous System Portrait: Stroke - R.S.: numbness in hand and unable to stand, suffered stroke (an interruption of blood to the brain that kills brain cells and causes he sudden appearance of neurological symptoms) - Ischemia – deficiency of blood flow to the brain due to functional constriction or to the actual obstruction of a blood vessel (ex. By a clot); can be treated with tissue plasminogen activator (t-PA) which breaks up clots, has to be given within 3 hours - Damaged right frontal cortex - Stroke – second leading cause of death - Neurons in brain are organized in layers and groups called nuclei – groups of cells forming clusters that can be visualized with special stains Neuroanatomy: Finding Your Way Around the Brain Describing Location in the Brain - Fig. 3.1 pg. 53 ** - Anterior or frontal = in front - Posterior = behind - Lateral = side - Medial = center or between - Coronal section = cut on vertical plane from crown of head - Horizontal section = viewed from looking down on a brain from above - Sagittal section = cut lengthways, front to back, and viewed from the side - Ipsilateral – same side; contralateral – diff; bilateral – if one structure lies on both sides - Proximal vs distal – close vs far apart - Afferent vs efferent – movement towards brain and spinal cord vs. movement from brain to body - Spatial orientation of spinal cord in humans and animals is different – ―dorsal and ventral in quadrupeds is anterior and posterior in upright humans‖ A Wonderland of Nomenclature - Precentral gyrus – the motor strip; M1 (primary motor cortex) - Longest name for brain structure – nucleus reticularis tegmenti pontis Bechterewi (NRTP) An Overview of the Nervous System Structure and Function - CNS – brain and spinal cord - PNS – everything else  Somatic NS ( cranial & spinal nerves) + Autonomic NS ( Sympathetic & parasympathetic division) - SNS – produces movement and transmits oncoming sensory information to the CNS (vision, hearing) - ANS – balances body’s internal organs to rest and digest through PNS (calming) nerves OR fight and flee or engage in vigorous activity through the sympathetic (arousing) nerves Support and Protection - Brain and spinal cord supported and protected from injury in Four ways: 1. Brain enclosed in skull and spinal cord in bony vertebrae; PNS can renew itself after injury (grow new axons and dendrites) 2. Triple layer set of membranes in skull - meninges a. Outer dura mater – tough double layer of tissue b. Arachnoid membrane – thin sheet of delicate tissue that follows contours of brain c. Pia mater – moderately tough tissue – clings to brain 3. Cerebrospinal fluid (CSF) – cushions from shock and pressure changes; circulates in ventricles, brain and spinal column, and subarachnoid space a. Hydrocephalus – if outflow of CSF is blocked; ―watery brain‖; severe mental retardation and possibly death 4. Blood-brain barrier – cells of capillaries are tightly packed and prevent any forms of blood-borne substances getting into the capillaries that leads to the CNS Blood Supply - To brain from 2 internal carotid arteries & 2 vertebral arteries (side of neck) - Anterior cerebral artery (ACA) – irrigates medial and dorsal parts of cortex - Middle cerebral artery (MCA) – lateral surface of cortex - Posterior cerebral artery (PCA) – ventral and posterior surfaces of the cortex - If an artery gets blocked by a blood clot, stroke symptoms will vary according to location of loss of blood – however other arteries can supply blood to the brain if there are connections between the arteries - Veins of brain through which blood returns to heart = external, internal cerebral and cerebellar veins Neurons and Glia - Neural stem cell – produce specialized cells that make up the brain and produce additional stem cells that persist in adulthood - Divides and produces 2 stem cells - Source of new neurons for certain parts of the adult brain - Give rise to progenitor cells that turn into blasts – non-dividing, primitive type of cells - Blasts  neurons or glial cells - New neurons are produced after birth in some regions of the brain - Sensory neuron – bipolar neuron; simple cell (body, axon, dendrite) - Somatosensory neurons – project from the body’s sensory receptors into the spinal cord; modified so that dendrite and axon are connected  speeds up connection (don’t have to pass through cell body now) - Interneurons – in brain and spinal cord; link-up sensory and motor-neuron activity in the CNS; dendrites branch extensively - Motor neurons – in brainstem; project to facial muscles and in spinal cord to the muscles of the body - Types of glial cells – Table 3.1 on page 58 Gray, White, and Reticular Matter - Gray matter = gray-brown colour from capillary blood vessels and cell bodies - White matter = axons that extend from cell bodies; axons coated with glial cells – thus white - Reticular matter = mixture of cell bodies and axons; molted gray and white; netlike appearance Layers, Nuclei, and Tracts - Tract – large collection of axons projecting to or away from a nucleus; aka fiber pathway - Carry info from one place to another - Nerves – fibers and fiber pathways that enter and leave the CNS and after they have entered they are called tracts (ex. Auditory nerve or vagus nerve) The Origins and Development of the Central Nervous System - Three regions of the primitive, developing brain - Prosencephalon ―front brain‖ – olfaction - Mesencephalon ―middle brain‖ - seat of vision and hearing - Rhombencephalon ―hindbrain‖ – movement and balance; spinal cord part of this - In mammals - Prosencephalon develops further to form the cerebral hemisphere = telencephalon ―endbrain‖ - Diecephalon – between brain – remaining part of old prosencephalon; includes thalamus - Back part further divides into metencephalon (across brain; cerebellum) and myelencephalon (low region of brain stem) - Human brain - Three part scheme – forebrain, brainstem and spinal cord - Never levels partly replicating work of older parts - Brain begins as a tube and remains hollow as it unfolds - Ventricles = 1-4; filled with CSF made by ependymal glial cells (adjcted to ventricles)  Lateral (first and second) – C-shaped lakes under cerebral cortex  Third and fourth – extend into brainstem and spinal cord The Spinal Cord Spinal Cord Structures and the Spinal Nerves - Categorized into 5 regions - 30 spinal cord segments (dermatomes) – 8 cervical, 12 thoratic, 5 lumbar, and 5 sacral - Dorsal root vs ventral root - Afferent fibers entering spinal cord (dorsal) converge as they enter the spinal cord - Efferent fibers leaving ventral part of spinal cord - Dorsally located tracts = sensory; ventral = motor - Inner part of cords are gray matter – organize movements and give rise to the ventral roots Spinal-Cord Function and the Spinal Nerves - Magendie – cute ventral and dorsal roots in puppies and found that by cutting dorsal root there was a loss in sensation and cutting the ventral roots cause loss of movement - Bell-Magendie Law – principle that the dorsal part of the spinal cord is sensory and the ventral is motor - Sherrington – spinal cord retains many functions even after separated from brain - Paraplegic – spinal cord cut so person no longer has control over their legs - Quadriplegic – cut is higher on the cord, so person cannot use their arms - Restoring connections between the brain and the cord can help restore function to those injured – BUT fibers in spinal tracts in adult mammals do not have the capacity to regrow - New growth is said to be prevented by the presence of certain inhibitory molecules on tracts of the cord below the cut - Scarring is another possible factor as to why there is inhibited growth in the injured areas; removing vs building bridges over scars – Tested on non human animals - Movements depends only on spinal cord function = reflexes – specific movements elicited by specific forms of sensory stimulation - Pain and temp receptors are smaller than those for muscles and touch - Flexion movements created by stimulation of pain or temperature that make the limb move inward, towards the body and away from the injury - Extension movements caused by the stimulation of fine touch and muscles receptors; move limb outwards, away from the body; limb maintains contact with the stimulus Connections Between central and Somatic Nervous Systems - Controlled by CNS - Brain overseas 12 pairs of crania nerves – have afferent functions (sensory input from eyes) and efferent (motor control of facial muscles) and some have both - Order of cranial nerves – On old Olympus’s towering top, and Finn and German view some hops. - Olfactory - Optic - Oculomotor - Trochlear - Trigeminal - Abducens - Facial - Auditory Vestibular - Glossopharyngeal - Vagus - Spinal accessory - Hypoglossal Automatic Nervous System Connections - ANS regulates internal organs and glands by connections through the SNS to the CNS - Sympathetic system arouses the body for action (ex, inhibiting digestion); parasympathetic system calms down the body (ex. Stimulating digestion) - Activation of the sympathetic system starts in the thoratic and lumbar spinal-cord regions - Spinal cord is connected to a chain of autonomic control centers – collections of neural nerves called sympathetic ganglia which control the internal organs - Greater part of parasympathetic system derived from three cranial nerves – vagus nerve (calms most internal organs), oculomotor nerve (controls pupil dilation and eye movements) and facial nerve (controls salivation) - Parasympathetic system connects with para. ganglia near target organs - Referred pain – pain in internal organs is perceived as coming from the outter part of the body – ex. Pain in heart = felt in shoulder and arm and kidney pain= in back The Brainstem - 3 main regions - Diencephalon - Midbrain - Hindbrain The Hindbrain - Cerebellum – surface gathered in folia (narrow folds) - Coordinating and learning skilled movements; damage  equilibrium problems, postural defects, and impairment to motor activity - Reticular formation – aka reticular activating system; Mouruzzi and Magoun = function of this are is controlling waking and sleeping – maintain general arousal or consciousness; within core of hindbrain The Midbrain - 2 subdivision - Tectum – roof of the third ventricle; dorsal – receives sensory info from eyes & ears  Superior colliculi – upper hills; projections from retina and mediate auditory related behaviors  Inferior colliculi - lower hills; projections from ears; mediate auditory- related behaviors; orientation of movements related to sensory input (turning head to look at source of sound) - Tegmentum – floor of the third ventricles; ventral  Red nucleus – limb movements  Substantia nigra – connected to forebrain; reward and initiating movement  Periaqueductal gray matter – controlling species-typical behaviors and modulating responses to pain The Diencephalon - Between brain - 3 structures: - Hypothalamus – lower room  22 nuclei ; takes part in nearly all parts of motivated behavior – feeding, sexual behavior, sleeping, moving, emotional behavior - Epithalamus – upper room  Overall function poorly understood  Pineal gland – secretes melatonin (influences daily & seasonal body rhythms  Habenula – regulates hunger and thirst - Thalamus – inner room  Largest structure  20-odd large nuclei that route info from 3 sources of cortex 1. Info from sensory systems to appropriate targets; LGB – visual projections; MGB – auditory projections; VLP – touch, pressure, ad pain projections from the body 2. Info between cortical areas – posterior cortex sends projections to the pulvinar nucleus (P) 3. Info from forebrain and brainstem regions - Almost all info received by the cortex is first relayed through the thalamus The Forebrain - Two subcortical – basal ganglia and limbic system The Basal Ganglia - Collection of nuclei laying beneath the anterior regions of the cortex - Putamen – shell - Globus pallidus - pale globe - Caudate nucleus – tailed nucleus – receives projections from all over the cortex and sends its own projections through the putamen and globus pallidus to the thalamus and then it goes to the frontal cortical areas - Movement and simple forms of learning The Basal Ganglia and Movement - Damage to different part of basal ganglia can result in changes in posture, increases or decreases in muscle tone and abnormal movements – jerks, tremors, and twitches - Diseases of basal ganglia – disorder of controlling movement 1. Huntington’s Chorea – genetic; cells die progressively; involuntary movements occur continuously – dancelike quality of the movements = in Latin that’s what Chorea means 2. Parkinson’s disease – projections from the substantia nigra to basal ganglia die; rigid & problems moving and maintaining balance; rhythmic tremors of hands and legs 3. Tourette’s syndrome – involuntary motor tics ( face and head); complex movement such as hitting or jumping; involuntary vocalizations (curse words of animal sounds) - Role of basal ganglia = control and coordination of movement patterns The Basal Ganglia and Learning - Support stimulus-response, or habit, learning - People with basal ganglia disorders can have difficulty performing such stimulus- response actions such as turning the handle to open a door or flicking a light switch to turn it on The Limbic System - Reptilian brain/ limbic lobe – coined by Broca; sandwiched at the border between the new brain and the old brain - Connections exist between the olfactory system and the limbic system – thus structures came to be called rhinencephalon (Smell-brain) - Consists of the amygdala, hippocampus, septum - Cingulate cortex – strip of limbic cortex that lies above corpus callosum - Septum and amygdala – roles in emotion and special-typical behaviors - Hippocampus – mediate memory and spatial navigation and vulnerable to effects of stress - From limbic ―lobe‖ to limbic ―system‖ - Papez – suggested that emotions is a product of the limbic system - Emotional brain = circuit of info that flows from the bodies in the hypothalamus  anterior thalamatic nucleus  cingulate cortex  hippocampus  mammillary bodies - Ideas could come from other parts of the brain and ultimately in the end influence the hypothalamus to release a hormone to prompt the appropriate physical response to the ideas and its emotional corollary - Limbic system was proposed to be the memory system of the brain (H.M) - Today, although some limbic structures play roles in emotional and sexual behaviors, it also serves other functions in memory, motivation and rewrd, and navigation The Neocortex - Cortex – refers to any outer layer of cells - 80% by volume of the human brain - Unique to mammals - Create and respond to perceptions in the world - Consists of 6 layers of cells (gray matter) and is 1.5-3.0 mm thick (2500 square cm) - Four lobes – frontal, parietal, occipital and temporal - Frontal lobes are bound by the central sulcus, inferiorly by the lateral fissure and medially by the cingulate sulcus - Anterior boundary of the parietal lobes is he central sulcus, inferior is the lateral fissure - Temporal lobes – dorsally bound by lateral fissure Fissures, Sulci, and Gyri - Cleft = called a fissure if it extends deeply enough into the brain to indent the ventricles; sulcus if its shallower - Ridge = gyrus - Cingulate gyrus located just above the corpus callosum, spans the length of the inner surface of the four neocortical lobes Organization of the Cortex in Relation to its Inputs and Outputs - Projection map – constructed by tracing axons from sensory systems into the brain and those from the neocortex to the motor system of the brain stem and spinal cord - Inputs to the cortex are relayed through the thalamic nuclei - Parietal, temporal and occipital lobes – considered largely sensory - Frontal lobes – motor functions - Parietal lobes – body senses - Temporal lobes – temporal lobes - Occipital lobes – visual functions Primary Areas - Structures that receive projections from structures outside the neocortex or send projections to it = primary areas Secondary Areas - Interpret sensory input or organize movement - Less directly connected with the sensory receptors and motor neurons Tertiary Areas - Encompass all cortex that is not specialized for sensory or motor function but mediates complex activities such as language, planning, memory and attention Snapshot: Imaging the Conversion Reaction - Conversion reaction – once called hysteria - Variety of disorders, mainly in women, including paralysis and other illnesses that could not be explained as physical ailments - Hippocrates – if the uterus wandered in the body and became lodged in a particular body part, the functional blockage of the part resulted in a patient’s symptoms - Brain imaging reveals changes in functions of certain brain regions - As participants attempted limb movements, regional cerebral blood flow was decreased in the paralyzed patients left dorsalteral prefrontal cortices but in the right of the feigners - Paralysis is associated with the brains executive control of movement Cellular organization of the Cortex - Neurons of neocortex arranged in 6 layers - Layers V ad VI send axons to other brain areas – areas and cells are particularly large and distinctive in the motor cortex, which sends projections to the spinal cord (large size = long distance) - Layer IV – receives axons from sensory systems and other cortical areas – large number of small, densely packed cells in the primary areas of vision, somatosensation, audition, and taste-olfaction - Layers I, II, and III – receive input mainly from layer IV and are quite well developed in the sensory and tertiary areas of cortex - Cytoarchitectonic map = map based on the organization, structure and distribution of cortical cells - Broadmann’s map = divided the brain at the central sulcus and examined the front and back halves separately; one problem is that current techniques have shown that many of the areas can be further subdivided Connections Between Cortical Areas - Neocortical regions are interconnected by 4 types of axon projections - Long connections between lobes - Relatively short connections between one part of a lobe and another and another - Interhemipheric connections (commissures) between one hemisphere and the other - Connections through thalamus - Interhemispheric connection link homotopic pointin the two hemispheres (contralateral points that correspond to each other) – act as zippers to link the two hemispheres - Two MAIN – corpus callosum & anterior commissure The Crossed Brain - Each of the hemispheres responds mainly to sensory stimulation from the contralateral side of the body or sensory world and controls the musculature on the contralateral side of the body - Visual pathways are arranged to ensure that each hemisphere gets visual info from the opposite visual field - Decussations of the sensory and motor fibers – numerous crossings; found along the center of the nervous system - Damage to a hemisphere produces symptoms related to perception and movement related to the opposite side of the body Chapter 12 – Variations in Cerebral Asymmetry Portrait: Individual Responses to Injury - A.B. and L.P. suffered two similar brain injuries but responded very differently - Injury to the posterior part of the left temporal lobe - A.B. had verbal difficulties, in reading, speaking and remembering words - L.P. had trouble recognizing faces and drawing pictures - A.B – right-handed man; L.P. left-handed woman - L.P. found to have language in the right hemisphere thus no language impairments Handedness and Functional Asymmetry - 10% of the population are left-handed; with broader criteria – 10 – 30% Anatomical Studies - Hand-preference is correlated with differential patterns of right-left asymmetry in the parietal operculum, frontal cortex, occipital region, vascular patterns, and cerebral blood flow - A lot of left-handed people show no asymmetry or a reversal of left and right anatomical symmetries - Left- and right- handers with speech in the left hemisphere had a mean right-left difference of 27 degrees in the angle formed by the vessels leaving the posterior end of the Sylvian fissure; vs. speech in right hemisphere – 0 degrees - More fibers descend to the right hand both from the contralateral left hemisphere and the ipsilateral right hemisphere than to the left hand - Difficulty in accounting for variations in anatomical asymmetries is that some left- and right-handers show a marked dissociation between structural and functional asymmetry - A large amount of the right-handed studies do not show the expected asymmetries but have reversed asymmetries or none at all - Studies in mice – gene Lmo-4 that is asymmetrically expressed and may be related to paw preference - Male right-handers have a deeper Sylvian fissure on the right than on the left; no dif in left-handers - Size of corpus callosum = 11% larger in left-handed and ambidextrous people than right- handed people Functional Cerebral Organization in Left-Handers - Although a small proportion of left-handers have bilateral speech or right-hemisphere speech, the majority of left-handers do not - Familial left-handers – have history of left-handedness vs nonfamilial left-handers - Nonfamilial l-h with unilateral lesions perform like right-handed patients; familial l-h patient perform differently, suggesting that they have a different pattern of cerebral organization - There is a larger incidence of l-h among mentally defective children and those with neurological disorders than is found in the general population Theories of hand Preference Environmental Theories - Behavioral Utility  Sword-and-shield theory  Soldier who held his shield in the left hand better protected his heart  improving survival chances; right hand became more skilled at various offensive and defensive movements, and eventually was used for most tasks  Female-oriented hypothesis version – it is adaptive for the mother to hold an infant in her left hand, to be soothed by the rhythm of her heart; right hand did skilled movements  Problem = failure to consider the probability that right-handedness has preceded behavior is is responsible for it rather than having been caused by it - Environmental reinforcement  Handedness is established by a bias in the environment  Child’s world is right-handed in many ways, which reinforced the use of the hand  Taught to write with the right hand, and thought left hand was unclean  Does not account for biological factors – diffs between patterns of familial and nonfamilial handedness or relation of handedness to cerebral dominance  When given the choice to choose left or right- handedness, left-handedness rose by 10% in school settings (norm) - Environmental accident  Genetically determined bias towards r-h  L-h develops through a cerebral deficit caused by an accident  L-h and neurological disorders in twins – 18% of twins are l-h & twins also show high incidence of neurological disorders (due to intrauterine crowding during fetal development and stress during development)  There is no/little support for such a theory that left-handedness is a form of brain injury Anatomical Theories 1. R-h to enhanced maturation and greater development of the left hemisphere – nonfamilial l-h will show an asymmetry mirroring that of r-h; familial l-h – show no asymmetry 2. Left-side bias for the localization of the heart, the size of the left temporal cortex in humans, and size of the ovaries in birds; many animals have a left-sided developmental advantage that is not genetically encoded; predominance of left- favoring asymmetries put the left-hemisphere speech dominance in the more general, structural perspective of all anatomical asymmetries Hormonal Theories  Brain plasticity can modify cerebral asymmetry significantly early in life, leading to anomalous patterns of hemispheric organizations  Testosterone in altering the cerebral organization – dif in levels may influence cerebral organization especially if the receptors were asymmetrically distributed  Higher than normal levels will slow down development – inhibition of the left hemisphere  altered cerebral organization  left-handedness  Testosterone also affects the immune system  more diseases related ot malfunctions in the immune system  Bulk of evidence doesn’t support this model  Does show however that l-h at a greater risk for asthma and allergies & arthritis is more preventable in right-handers Genetic Theories  Recessive gene for l-h  Annette’s model accounts for 12.5% of the population as being l-h  Theory doesn’t predict the number of l-h with right-hem speech nor attempts to differentiate between familial and nonfamilial l-h - Little doubt that the major factor in cerebral asymmetry is the asymmetrical representation of language and spatial functions rather than handedness Sex Differences in Cerebral Organization - On average women tend to be more fluent than men in using language and men tend to perform better on spatial analysis Sex Differences in Behavior Motor Skills - Men are superior in throwing objects and are superior at intercepting objects thrown towards them - Differences present in children as young as 3 years old - Chimpanzees show a similar sexual dimorphism - Women have superior fine motor control and surpass men in executing sequential and intricate hand movements Spatial Analysis - Men are superior at mental rotation of objects and at spatial navigation tasks - Men have better overall map knowledge than women - Women are better than men at identifying which objects were moved and have better recall for landmarks along the route - Spatial info is not the critical factor – how the spatial info is to be used is the difference in sex Mathematical Aptitude - on average, men do better at tests of computation - Stanley study with children and Scholastic Math Test – sex differences increased as the scored increased - Looking at the children with only the highest scores they found that there were 12x as many ―gifted‖ boys as girls at the top - Found worldwide across different cultures Perception - Women are more sensitive to all forms of sensory stimuli, except for vision - Women are more sensitive to facial expressions and body postures than men - Women have lower threshold for stimuli detection and they detect sensory stimuli faster - Males have the advantage of drawings of mechanical objects such as bicycles – no general advantage in drawing Verbal Ability - Women superior on test of verbal fluency and they have a superior verbal memory - Girls begin to talk before boys Aggression - Physical aggression is more prevalent in men than women - Research in animals – aggression in males is probably due to testosterone pre- and postnatallly Genes or Experience? - Most or all these differences are found in both children and adults and the differences are largely unaffected by training - Some sex differences seem unrelated to life experience - Drawing the water level in tipping jars – women constantly underperform and the difference is seen in both young and old - Difference in performance is not due to the inability of women to understand the concept that the water line will always be horizontal, but rather that women are affected by the tilt of the jar than men are - Dif remains even if women are given training Sex Differences in Brain Structure - Men’s brains were 100 grams heavier than women throughout the range of body sizes - 4 billion more neurons in male brains and body size didn’t account for the difference - Men have a small advantage in IQ scores - Female brains appear to have large volumes in regions associated with language functions, in medial paralimbic regions, and in some frontal lobe regions - Women have a greater relative amount of gray matter and they have more densely packed neurons - Men have a larger medial frontal and cingulate region, a larger amygdala, and a larger hypothalamus - Men also have larger overall white matter volume and larger cerebral ventricles - Males have more-uniform gray-matter concentration, females have a patchwork of concentration differences – increased concentration in peri-Sylvian fissure regions could be related to the female advantages in fine motor skills - Increased cortical thickness in females throughout the cortex – thickness greatest in parietal and posterior temporal regions - Females have a more complex patterns of gyrification in the cortex – dif in underlying cytoarchitecture and connectivity - * Gray matter in females is organized differently such that it offsets the difference in volume - Little is known about how size relates to cognitive functions within each sex Influence of Sex Hormones - Sex dif in brain structure has been related to difs in distribution of androgen and estrogen during development - Due to the differences in distribution of receptors of gonadal hormones during development - Ate of cell death in the course of aging may be higher in men than women (especially in frontal lobe) so there is a possibility that some of the sex differences are not present in childhood Establish Asymmetries - Reliable sex differences in anatomical asymmetry 1. Larger asymmetry in males (left 38% larger) in the planum temporale 2. Horizontal component was longer in the left hemisphere of both sex, men had a larger horizontal component in the left hemisphere; sex dif in the organization of language-related functions 3. Asymmetry of the planum parietale (right hem) is twice as large in males 4. Posterior part of the callosum in women is larger; women have a larger anterior commissure than do men, even without correcting for brain size – dif likely due to the number of neural fibers in the two sexes 5. Ridges on our finger prints are asymmetrical – more ridges on our right fingerprints; women far more likely to show an atypical pattern; patterns of ridges is correlated with performance on certain cognitive tests - Right testicles tend to be bigger than left; breasts tend to be larger on the left than the right – dif is found in fetuses The Homosexual Brain - Sexual orientation is related to performance on test - Homosexual men outperform all groups on verbal fluency, where heterosexual women outperform heterosexual men, and homosexual women have the lowest scores - Heterosexual men outperform heterosexual women in throwing abilities, where homosexual men throw less accurately and homosexual women throw more accurately than their counterparts Sex Differences Revealed in Imaging Studies - **Fig. 12.6 - EEG, MEG, and fMRI studies show more asymmetrical activity in men than women particularly in the language-related activities - Blood flow shows that women have more rapid overall blood exchange possibly because of the density in the neurons or the distribution of gray matter and white matter - Presumably the anatomical difs correspond to the functional differences Research with Neurological Patients - Two types of lesion-related differences are possible o Degree of asymmetry in lesion effects – if the two hemispheres were more similar functionally in one sex than in the other sex; men might show more asymmetrical effects of unilateral lesions o Intrahemespheric organization - injury to frontal lobe may have greater effects in one sex than in another – consistent with greater relative volume of much of the frontal lobe of women - Evidence for both - Assess asymmetry by looking at the effects of the lesions on general tests of verbal and nonverbal abilities and look at the differences of the results - Although left- and right-hemisphere lesions in men affected the verbal and performance subscales; left-hem lesions in women depressed both IQ scores equally, and right-hem lesions in women failed to depress either IQ scores - Men with right-hem lesions were more disrupted than women were on the performance IQ - Women could be more likely to use verbal strategies to solve the WAIS tests - Men and women are almost equally likely to be aphasic subsequent to the left-hemisphere lesions - Men more likely to be aphasic and apraxic after damage to left posterior cortex while women are likely to experience speech disorders and apraxia after anterior lesions - Anterior lesions in right-hem in women – impaired performance on block-deisgn and object-assembly subtests; men – equally affected on tests by anterior or posterior lesions - Left-hem damage in infancy is known to lead to the shifting of language to the right-hem; epileptic patients study revealed that girls with left-hem damage after 1 year of age were more likely to show reorganization and boys were likely to shift language perhaps as late as puberty - **Male brain may be more plastic after cortical injury Explanations of Sex Differences Hormonal Effects - In birds and mammals, testosterone during the developmental period has effects on the organization of hypothalamic and forebrain structures, and the observed morphological effects are believed to be responsible for the behavioral dimorphism - Inductive (or organizational) effect - influence of gonadal hormones on the brain and behavioral development which leads to sexual differentiation - Androgen is converted into estradiol and the binding of estradiol to receptors leads to masculinization of the brain - Estradiol has not been found in adults, but in the developing rodents and nonhumans - High estrogen levels are associated with depressed spatial ability and enhanced articulatory and motor capability - Greater blood oxygenation was found in a variety of cerebral regions at low estrogen time points vs high-estrogen time points (such as amygdala, hippocampus, and frontal lobe) with high arousing (negative valence) stimuli - Estrogen also directly affects the structure of neurons – in female rats there are large changes in the in the number of dendritic spines on hippocampal neurons - Female rats and removes ovaries – increase in dendritic spines and cortical neurons - Testosterone levels in men are higher in the fall and in the morning - Spatial scores fluctuate with testosterone levels – men with lower testosterone levels have highest scores - Men perform better on spatial tests in the spring and evening - Lower average testosterone do better on spatial and mathematical reasoning tests - Women with higher testosterone levels do better on cog activities - Testosterone blockages affect verbal memory and attention but NOT nonverbal memory - Cog effects can be reversed with estradiol – metabolite of testosterone - Estrogen treatment in menopausal women – improves verbal fluency and verbal and spatial memory – findings controversial - Critical period hypothesis – estrogen has max beneficial effects on cognition in women when it is initiated closely in time to natural or surgical menopause - Neurons become less sensitive to estrogen after a prolonged period without the hormone/ its possible that a lot of neurons have died and its impossible to reverse the effects of aging - Exposure to gonadal hormones perinatally determines later ability of environmental stimulation to alter the synaptic organization of the cerebrum - Female hippocampus is more fluid in new environments than male hippocampus – plasticity depends on estrogen - Cognitive functions may diverge functionally at puberty and begin to converge again after menopause – no known testing Genetic Sex Linkage - Recessive gene on the X chromosome is postulated to be responsible for determining variations in spatial ability - If a gene for a particular trait is recessive, it will not be expressed in a girl unless the recessive gene is present on both X chromosomes - If mother carries gene on both X chromosomes, all her sons will have the trait, but the girl will only have the trait if her father also carries the recessive gene on his X chromosome - Hypothesis has yet to be proven Maturation Rate - Earlier evolution of cerebral asymmetry in girls - Male brains might mature slower than the female brain; maturation rate is a critical determinant of brain asymmetry - More slowly a child matures, the greater the observed cerebral asymmetry - Early-maturing individuals (despite sex) do better on test of verbal abilities than on tests of spatial ones - Maturation rate may affect the organization of cortical function Environment - Although environmental theories may be appealing, there is no evidence that environmental or social factors can solely account for observable differences in verbal and spatial behavior - Ex. Horizontal line of liquid when tilted – even with training, women failed to show much improvement and claimed that the water is level in the bottle when its upright but inclined when the bottle’s titled Preferred Cognitive Mode - Different modes of cognitive analysis in women and men - Women solve problems based on verbal modes – which is less effective at solving spatial problems, women exhibit apparent deficit - Women should do better on verbal tasks but this hasn’t been investigated yet Conclusions - Biology likely plays a part in the observed sex differences - Ex. Sex and handedness – sex differences in verbal and visuospatial behaviors varies as a function of handedness - Neurological factors may be modulated by the environment partly account for sex-related differences Environmental Effects on Asymmetry Culture and Language - Asian languages might promote right-hem participation because the Asian languages appear to have more prosody (song) and the reading of pictoral Chinese characters requires more spatial processing - All oral language is probably located in the left hem in bilingual people - There is no change in organization of the brain for those individuals with exposure to multiple languages - Language acquired later in life may activate different frontal regions from those activated by first languages or seconds languages acquired early in life - Japanese writing consists of phonograms (kana) and ideograms (kanji) - Each phonogram represents a spoken sound - Ideogram represents a unit of meaning which may correspond to a word or words - Brain may process the two types of characters differently however there is no clear evidence to suggest this - Some imaging evidence supports the idea that alphabetic language and kanji might be processed differently – phonological task activated large regions of the left hemisphere where the semantic task activated the right inferior frontal cortex = result not seen in semantic matching Sensory or Environmental Deficits - Educational and congenital deafness are alleged to alter hemispheric specialization Brain Organization in Nonhearing People - Left-hem damage produces aphasia in people who converse by using ASL possibly because of praxic requirements - Congenital deafness may alter cerebral processing - Congenitally deaf persons show the usual right-visual-field superiority in tasks of linguistic processing – could be that if experience with auditory language is absent, lateralization of some aspect(s) of nonauditory language function is abolished; or could be a result from strategy differences due to absence of auditory experience - During the perception of line drawings, visual evoked potentials are larger on the right in children who use ASL and no asymmetry appears in children who who are deaf and cannot sign but use pantomime = Deaf signers acquired their visual signing symbol much as hearing children acquired auditory verbal symbols: with the left hemisphere - Lack of asymmetry in nonsigners could mean that the absence of language experience somehow abolishes certain aspects of cerebral asymmetry, OR that expression of cerebral asymmetry depends on language experience - 34 congenitally deaf subjects with unilateral brain injury = left-hem patients – performed poorly on all measures of language use and right-hem poorly on the visuospatial tasks – exactly what would be expected in hearing people  exposure to spoken language was not necessary for hem specialization Environmental Deprivation - Genie – adolescent girl who endured 12 years of extreme social and experiential deprivation and malnutrition - After discovering her, her cognitive development was rapid, but her language lagged behind other abilities - Strong left-ear effect for both verbal and nonverbal sounds - Right hemisphere seemed to be processing both verbal and nonverbal acoustical stimuli – a case with people who have had a left hemispheroctomy - 3 explanations for the abnormal lateralization: 1) Disuse of left hem  degeneration – unlikely 2) Absence of auditory stimuli  left hemisphere lost the ability to process linguistic stimuli 3) Left hem was either being inhibited by the right hem or by some other structure or it was performing other functions - Abandoned Romanian children warehoused by the communist regime in orphanages  little environmental stimulation  children adopted into homes  even after placement in excellent conditions, the effects of early experience on their brain development is long lasting - Reduced brain size by 20% and significant cog and behavioral problems Epigenetics - Changes in gene regulation that takes place without a change in DNA sequence - Changes in gene expression may occur spontaneously or in response
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