Flashcards in Cerebral Asymmetry Deck (34):
What is the general function of the left hemisphere of the brain?
-Controlling movement on the right side of the body
What is the general function of the right hemisphere of the brain?
-Perceiving and synthesizing nonverbal information
-Controlling movements on the left side of the body
What are the anatomical asymmetries in the brain?
-Right hemisphere is larger and heavier, contains more gray matter
-Temporal lobes have marked asymmetry (planum temporale (Wernicke's area) is larger in the left hemisphere; primary auditory cortex (Heschl's gyrus) is larger in the right hemisphere)
-Asymmetry in the temporal lobes is correlated with asymmetry in the thalamus
In which areas of the brain do the neurons have more dendritic spines? Why?
-Left frontal operculum and left precentral cortex
-More locations for enhancement or suppression of graded potentials in the dendritic tree
What is a commissurotomy? What happens in patients with this?
-Surgical procedure to sever the corpus callosum
-Sensory information is sent to only one hemisphere
-Left hemisphere has access to speech brain areas, right brain does not
-When left hemisphere sees spoon in right visual field, the subject responds correctly
-When right hemisphere sees spoon in left visual field, the subject does not respond
-Illustrates right hemispheres role in facial recognition
What is the carotid sodium amobarbital injection?
-Injected into carotid arteries, anesthetizes hemisphere
Describe asymmetry in the visual system
-Tachistoscope used to present info to each hemisphere independently
-Infer which hemisphere is better at processing certain types of info by looking at accuracy of identification in each visual field
Describe asymmetry in the auditory system
-Simultaneous presentation of two different stimuli to left and right ears
-Recalled more digits presented to right ear
-Right ear advantage for verbal stimuli (speech) (left hemisphere)
-Left ear advantage for music and stimuli with tonal quality (right hemisphere)
Describe asymmetry in the somatosensory system
-Subjects blindfolded and asked to perform various tasks with their hands
-Braille read more rapidly with right hand
-Left hand or right-handed subjects superior at identifying shapes, angles, and patterns
Describe asymmetry in the motor system
-In direct observation, right side of mouth opens wider and more quickly for verbal and nonverbal. Onset of facial expressions sooner on the left side of the face
-Interference tasks. Simultaneous performance of two tasks (playing piano songs with two different hands). Speaking disrupts right hand, humming disrupts left hand
What are the two types of preferred cognitive mode?
-Left hemisphere people: Analytical, logical, verbal, meticulous
-Right hemisphere people: Concerned with organizing concepts and visualizing meaningful wholes
What are the anatomical differences in people who are left-handed compared to right-handed?
-Left-handers show more variation in asymmetry
-More fibers descend to right hand
-Sylvian fissure is deeper in left-handers
-Greater hemispheric interaction in left handers
What are the environmental theories of hand preference?
-Behavioural utility (proposes left hand is for holding baby/shield, thus leaving right hand to perform skilled tasks)
-Environmental reinforcement (bias in environment)
-Environmental accident (genetic bias towards right-handedness, left-handedness develops from cerebral deficit, twins have more incidents of left-handedness possible due to increased stress in the womb)
What are the hormonal theories of handedness?
-Testosterone (different levels of testosterone influence cerebral asymmetry, higher testosterone = increased likelihood of left-handedness)
-With amniocentesis, increased testosterone did not result in increased left-handedness
What are the five cognitive behaviours that men and women differ in?
How do men and women differ in motor skills?
-Men superior at throwing and intercepting objects
-Women superior at fine motor skills
-Both present in young childrens
How do men and women differ in spatial analysis?
-Men superior at mental rotation and spatial navigation
-Women superior at spatial memory
How do men and women differ in mathematical aptitude?
-Men superior at mathematical reasoning
-Women superior at computation
How do men and women differ in perception?
-Women more sensitive to all sensory stimuli except vision
-Men superior at drawing mechanical objects
How do men and women differ in verbal ability?
-Women have superior verbal fluency and memory
-Outperform men on Chicago word-fluency test (think of words starting with particular letter)
What are the sex differences in the anatomical structure of the brain?
-Male brain is larger than the female brain
-Females have larger volume in areas associated with language, in medial paralimbic regions, and some frontal lobe regions
-Males have larger medial frontal cingulate region, amygdala and hypothalamus, ventricles, and overall white matter
-Men have more neurons, but women have more dendrites and axons
-Increased cortical thickness in females
-Females have more complex patterns of gyrification
What are the influences of sex hormones in the brain?
-Sex differences in brain appear due to distribution of estrogen and androgen receptors during development
-Women --> frontal and medial paralimbic regions
-Men --> medial frontal cortex and angular gyrus
How does the homosexual brain differ from the heterosexual brain?
-Hypothalamus in homosexual men differs from heterosexual men and women
-Homosexual men outperform all groups on verbal fluency
-Homosexual women throw more accurately than heterosexual men
What is the difference in asymmetry in men and women with lesions?
-Differences in verbal IQ and performance IQ in men and women with right and left hemisphere damage
-Women perform more poorly on performance IQ with left lesions than men
-Men perform more poorly on performance IQ with right lesions than women
What differences does intrahemispheric organization cause in men and women with lesions?
-Differences in the appearance of aphasia (disturbance in comprehension and expression of language) and apraxia (inability to execute learned purposeful movements)
-Women have more apraxia and agraphia with damage to left frontal area
-Men have more apraxia and agraphia with damage to left posterior area
Why are sex differences present? What are the hormonal effects on organization?
-Organizing effect: Effects of hormones on brain organization leads to sexual differentiation. Assumed to take place during development
-Functional effects of hormones seen in adulthood: high estrogen associated with depressed spatial ability, estrogen affects neuron structure. Low testosterone associated with high spatial ability in men, optimal level of testosterone (also true for women). Hormone replacement in women increases verbal fluency and verbal and spatial memory
Why are sex differences present? What is the genetic sex linkage?
-Recessive gene on X chromosome accounts for spatial ability in girls
Why are sex differences present? What role does maturation rate play?
-Brain matures faster in girls
-Slower the brain develops, the more asymmetry appears
What role does the environment play in sex differences in the brain?
-Girls and boys are encouraged to engage in different activities leading to different abilities
-Not supported by bulk of evidence
What role does preferred cognitive mode play in sex differences in the brain?
-Women prefer to solve problems using a verbal strategy
What are the effects of hemispherectomy?
-Removal of right hemisphere - deficits on visuospatial abilities (complex)
-Removal of left hemisphere - deficits in understanding spoken language
-Hemispherectomy provides evidence against equipotentiality
Describe asymmetry in birds
-Left hemisphere dominance for songs
-Lateralization for visually guided functions (right eye focuses on food etc., left eye focuses on specifics of objects)
-Asymmetry for memory function
-One hemisphere sleeps at a time
Describe asymmetry in rodents
-Larger right hemisphere
-Left hemisphere dominance for species-specific calls
-Lateralized modulation of immune system - role in hormones