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Chapter 5

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University of Toronto Mississauga
Elizabeth Johnson

[LECTURE 4] CHAPTER 5: THE  CHILD’S GROWTH BRAIN ,BODY ,MOTOR  SKILLS AND  SEXUAL MATURATION BRAIN DEVELOPMENT IN INFANCY I. The prenatal period a. Brain grows rapidly b. Infant’s brain weighs ¼ as much as a mature brain, a 6 month old’s weighs ½, and a 2 year old’s weighs ¾ II. Largest portion of the brain consists of two connected hemispheres that make up the cerebrum (the two connected hemispheres of the brain) a. The covering layer of the human cerebrum (the cerebral cortex) i. Highly convoluted and contains about 90% of the brain cell’s bodies ii. Contains the cells that control specific functions like seeing, hearing, moving, and thinking NEURONS AND SYNAPSES I. Baby’s brain has most of its neurons at birth II. During the embryonic period, neurons multiply at a rapid pace in a process called neuron proliferation a. Neurons: a cell in the body’s nervous system consisting of a cell body, a long projection called an axon, and several shorter projections called dendrites; neurons send and receive neural impulses, or messages, throughout the brain and nervous system b. Neuron proliferation: the rapid proliferation (multiplication) of neurons in the developing organism’s brain III. Brain gets bigger b/c existing neurons grow and the connections between them proliferate IV. Glial cells a. Surround and protect neurons b. Also grow c. Provide neurons with structural support, regulate their nutrients, and repair neural tissue d. Some are responsible for myelination i. Parts of neurons are covered with layers of a fatty, membraneous wrapping called myelin ii. Makes the neuron more efficient in transmitting information iii. Most myelination occurs during the first two years of life but continues into adulthood V. Neurons are constantly moving VI. Neural migration is guided by neurochemical processes a. Ensures that all parts of the brain are served by a sufficient number of neurons b. Absence of sufficient neurons in their proper locations is associated w/ various forms of mental disability and disorders like dyslexia and schizophrenia VII. Synapses: connections b/w neurons a. the extended axon of one neuron transmits a message to the projected dendrites of another neuron, usually by means of chemicals that cross the small space b/w neurons b. crucial to surviving and learning i. as the brain’s neurons receive input from envt they create new synapses, allowing for complex communications VIII. Synaptogenesis: forming of synapses a. beings early in prenatal life (as soon as neurons begin to evolve) b. brain forms more synapses than neurons IX. 2 processes reduce the number of neurons and connecting fibres i. Neuronal death: death of some neurons that surround newly formed synaptic connections among neurons to make space for the new information ii. Synaptic pruning: the brain’s disposal of the axon and dendrites of a neuron that is not often stimulated; frees up space for new synaptic connections b. Increases speed, efficiency, and complexity of transmissions b/w neurons and allows room for new connections that develop as the child encounters new experiences SEQUENTIAL DEVELOPMENT OF THE BRAIN I. There is an orderly sequence to brain development during infancy a. Early months of life: move from mostly reflexive behaviour to voluntary control of movements i. Motor area of brain develops most rapidly b. 2 months old: motor reflexes (rooting, startle response) drop out and motor cortex begins to oversee voluntary movement (reaching, crawling, walking) i. In the visual cortex, the number of synapses per neuron is multiplied some six times within the first two years of life ii. Infants’ visual capacities are greatly enhanced (ex. become more skilled at focusing on objects at different distances) HEMISPHERIC SPECIALIZATION I. Hemispheres: the two, left and right, halves of the brain’s cerebrum a. Anatomically different b. Control different functions II. Corpus callosum: the band of nerve fibres that connects the two hemispheres L EFT AND  R IGHT  B RAIN  FUNCTIONS I. Hemispheric specialization: differential functioning of the two cerebral hemispheres II. Left hemisphere of motor cortex controls simple movement in the right side o the body III. Right hemisphere controls the body’s left side IV. Lateralization: the process by which each half of the brain becomes specialized for the performance of certain functions a. Right hemisphere i. processes visual-spatial information, non-speech sounds (music), perception of faces 1. If damaged, drawing skills may deteriorate, trouble following maps or recognizing friends, spatial disorientation ii. Processing emotional information 1. If damaged, can have difficulty interpreting facial expressions 2. Left hemisphere is activated in the expression of emotions associated with approach to the external environment (joy, interest, anger) 3. Right hemisphere is activated in emotional expressions that cause the person to turn away or withdraw from that environment (distress, disgust, fear) b. Left hemisphere i. Associated w/ language processing 1. People w/ damage may have trouble understanding what is said to them or speaking clearly 2. In deaf persons who use sign language (motor movements of hands) – right side of brain takes over language functions 3. Possible better processing of auditory and musical pitches C ONSEQUENCES  OF  BRAIN  LATERALIZATION I. Dyslexia: a term for difficulties experienced by some people in reading or learning to read a. Difficulty integrating visual and auditory information (ex. matching written letters or words to their sounds) b. Suggested that children w/ dyslexia don’t show normal lateralization pattern i. Process spatial information on both sides of the brain rather than primarily on the right, and thus their left hemispheres may become overloaded ii. Leads to deficits in language skills II. Handedness – another lateralized function a. 90% of adults are right handed and a majority of infants show right hand dominance b. Gene for handedness identified c. Many left handed people are ambidextrous – suggests brains may be less clearly lateralized than brains of right handed people THE BRAIN'S PLASTICITY: EXPERIENCE AND BRAIN DEVELOPMENT I. Plasticity: capacity of the brain, particularly in its developmental stages, to respond and adapt to input from the external environment II. 2 types of experience influence brain development a. Experiences like touch, patterned visual input, sounds of language, affectionate expressions from caregivers, nutrition i. All expected in normal environment ii. Trigger synaptic development and pruning iii. Critical for normal brain development iv. When there’s an interference, basic abilities are impaired 1. Ex. when children have congenital cataracts, their visual system is deprived of stimulation and fails to develop properly 2. When cataracts are removed, the adult is blind b. Experiences that are unique to individuals i. Encountered in particular families, communities and cultures ii. Brains respond to different environments by developing synaptic connections that encode specific and unique experiences 1. Ex. children in Mozambique develop aspects of the motor cortex that correspond to the skills associated w/ hunting and fishing 2. North American children develop parts of the brain that reflect the fine motor and eye hand coordination needed for success at video games III. Animal research shows that the size, structure, and biochemistry of the brain can be modified by experience a. Rosenzweig study i. Placed rats in 2 dif environments ii. ‘enriched’ envt w/ large, brightly lit communal cages with wheels and toys iii. ‘impoverished’ environment where each rat was alone in a bare cage in a dim room iv. Discovered that after 3 months, the weight of the cerebral cortex (controls higher-order processes) was 4% heavier for rats in enriched environment, and the weight of the occipital region (controls vision) was 6% heavier v. Enriched envt tends to increase the complexity of neurons as measured by the number of dendrites they develop 1. More dendrites = more synapses with other neurons 2. More information can be sent via these synaptic connections 3. Activity of key chemicals in the brain (esp in cerebral cortex) increases as a result of an enriched environment b. Adult rats exposed to impoverished or enriched envts after being reared in regular lab conditions show changes similar to those of young rats IV. Research on human infants also demonstrates the brain’s plasticity a. Infants respond to the sounds of all languages b. Become more selective over first year of life, responding increasingly to sound of own language c. Dif sets of neuronal connections become programmed to respond to particular aspects of speech, so infants’ brains develop ‘auditory maps’ or templates to respond to certain auditory features and not others V. Exposure to music can enrich brain development a. Natural harmonics of music may help brain develop a wiring diagram that promotes spatial- temporal reasoning b. Piano study i. After 6 months of weekly piano lessons, 3 and 4 year olds improved in this kind of reasoning as demonstrated by their ability to look at disassembled picture of an elephant and to know how to put it together ii. Children who received computer training or no stimulation showed little improvement VI. Some research demonstrates that the brain can undergo structural change based on unique experiences even in adulthood a. Looked at structure of brains of humans w/ extensive navigational experience (London taxi drivers) and compared w/ control subjects who did not drive taxis b. Found that the posterior hippocampi (associated w/ spatial representations of the envt) was larger in taxi drivers c. Suggests a remarkable degree of plasticity in the brain structure in response to envt demands VII. Lack of stimulation and exposure to traumatic events can damage the brain and cause it to malfunction a. In abused children the cortex and the limbic system (involved in emotion and infant parent attachment) are 20-30% smaller and have fewer synapses than non abused children b. Techniques such as PET scans (positron-emission tomography) also show the effects of early deprivation on the developing brain i. Under unstimulating and unresponsive envts, there is a reduced connectivity or communication between regions of the brain ii. Reduced cortical activity involving neurons acting together to solve a cognitive task such as memory or face processing MOTOR DEVELOPMENT HAND SKILLS I. Newborns display a grasping reflex and rudimentary form of reaching - ‘prereaching’ a. Involves uncoordinated swipes at objects they notice II. At 3 months, infants initiate a more complex and efficient pattern – ‘directed reaching’ III. By 5 months, generally succeed in reaching in for an object and successfully grasping it a. Involves muscle growth, postural control, control of movement of arms and hands IV. How reaching develops is consistent with the dynamic systems view of development (from chapter 1) a. One component of the dynamic system is visual perception i. If infant has nothing to look at, there’s no incentive to reach out b. Another component involves the motor ability to grip an object i. 4 month olds use touch to determine their grip while 8 month olds use vision (can preshape hand as they reach for an object) V. Over the first year of life, infants’ progress in controlling their hands is remarkable (become highly skilled reachers) a. Begin to use objects as tools b. Learn the use of gestures in social communication c. By age 2, use hands in play (ex. building a tower) d. By age 3, use hands to scribble with crayons LOCOMOTION I. Development of locomotion involves 3 phases a. 1 : when you hold a baby upright and let his feet touch a flat surface, tilting his body from side to side, the baby responds by reflexively moving his feet in a rhythmic stepping motion i. Reflex disappears by 2 months old nd b. 2 : during the second half of baby’s first year; reappearance of stepping movements rd c. 3 : about 1 year; infants begin to walk without support II. Theories of how walking develops a. Maturational theorists i. Depends on development of the motor cortex b. Cognitive theorists i. response to cognitive plans or representations that are the consequence of watching other people walk c. Thelen’s dynamic systems theory i. Walking skills are determined by the interplay of a variety of factors (Ex. emotional, postural) ii. Newborn stepping response disappears for 10 months before true walking emerges b/c of anatomical factors 1. Baby’s size and weight become too much of a load on emerging motor system rd III. Running well established by the 3 year IV. Hopping emerges b/w 2 and 3 years V. These skills depend on improvements in balance and coordination and the opportunity for practice HOW LOCOMOTION MAY AFFECT OTHER ASPECTS OF DEVELOPMENT I. Increased independence as result of ability to walk a. Can explore envt more fully and initiate more contact w/ other people b. Leads to increased parent-child interaction – babies can move from place to place and make a mess/get into a dangerous situation II. ‘perception-action coupling’ approach a. Motor/action systems are functionally interrelated to sensory or perceptual systems such that changes in one aspect influence the development of the other aspect b. Locomotion can change the way babies understand their perceptual world i. Ex. beginning of crawling = fear of heights, spatial abilities c. Locomotion possibly helps infants deal better w/ changes in spatial orientation i. Study where crawling babies were better at precrawling babies at finding a hidden toy that was moved III. ‘moving room’ experiments a. Room in which walls and ceilings can be moved back and forth while the floor stays immobile b. 3-6 year olds will only sway back and forth to visual movement c. Self produced locomotion is critical for infants’ use of visual information in such situations i. Crawling infants but not precrawling ones used moving room input to control their balance THE ROLE OF EXPERIENCE AND CULTURE I. Cross cultural studies a. When parents give babies special physical attention (massage, exercise) infants achieve motor milestones somewhat earlier i. Zambia – mothers carry new babies in sling on backs; when sitting, leave infants sitting alone, where they can practice the development of motor skills ii. Jamaica – mothers massage infants, stretch arms and legs, let practice stepping; children also are motorically advanced iii. Zinacantecos of Mexico – infants tightly swaddled for first 3 months, have less advanced motor skills iv. Chinese families – babies put on pillows, crawling restricted; some infants fail to develop adequate strength in muscle groups critical for crawling; crawling is delayed II. Geographic region where children are reared may influence motor development a. Infants born in summer months or fall months acquired motor skills later than winter-spring infants b. Summer/fall infants would begin developing motor skills in winter time when there are shorter days, cold temperatures and restrictive clothing (more difficult to move) PHYSICAL GROWTH I. Study of physical growth is guided by 2 classic principles a. Growth characterized by cephalocaudal development i. Growth occurs from the head downward ii. Brain and neck develop earlier than legs and trunk b. Growth follows a proximal-distal pattern i. Centre outward ii. Internal organs develop earlier than arms and hands II. Height and weight a. 2 principal measures of overall growth b. Babies grow faster in first half of life than ever again c. Nearly double their weight in first three months and triple it by end of first year d. Top heavy light bulb shaped bodies become cylindrical e. Centre of mass moves from sternum to below the belly button f. Growth is episodic rather than continuous DO GENES AFFECT HEIGHT AND WEIGHT? I. Research suggests genetic factors strongly influence height and weight a. May determine as much as 2/3rds of variance b. Identical twins are twice as likely to resemble each other in weight as fraternal twins c. Twins reared apart w/t a common envt still show similarity in weight II. Gender has a clear effect on height and weight a. Girls taller than boys from 2 to 9 b. At 14 girls’ height plateaus but boys continue to grow until they’re 18 c. Girls tend to weigh less than boys early on and then exceed them in weight until 14 when boys’ weight continues to accelerate THE INFLUENCE OF ENVIRONMENTAL FACTORS N UTRITION BOTTLE VS. BREASTFEEDING I. Breastfeeding is best for babies’ healthy development a. Benefits of breastfeeding: i. Protection against infectious disease (strengthens immune system) ii. Better development of the brain and nervous system iii. Reduction in likelihood of sudden infant death syndrome (SIDS) iv. Supports appropriate weight gain v. Builds denser bones vi. Promotes efficient absorption of iron and therefore lessens likelihood of iron deficiencies b. Study: i. Children in Britain and New Zealand who have been breastfed were found to have higher intelligence than bottle fed children but only if they had a specific genetic makeup 1. Children who were genetically predisposed to benefit from fatty acids present in breast milk showed the advantage in IQ II. Benefits for mothers a. More convenient (no warming up or refrigeration required) b. Helps women lose weight gained during pregnancy c. Delays ovulation d. Promotes closeness b/w mother and baby e. Lower cost (formula is expensive) i. Women in developing countries usually dilute formula to make more which endangers health of babies ii. Lack of clean water in developing countries = infected formula III. Breastfeeding habits in the USA a. 60% of mothers breastfeed for several months b. After 6 months, baby starts eating solid foods and rate of breastfeeding drops c. Women over 25, better educated, and of higher socio-economic status are more likely to breastfeed d. Some women are unable to breastfeed due to medical conditions (AIDS, tuberculosis) NUTRITION AND PHYSICAL GROWTH I. Nutrition plays a controlling role in physical growth II. Evidence from wartime restrictions on food consumption st nd a. Trend toward less growth during 1 and 2 World Wars b. Nutritional factors can affect age at which children enter puberty nd i. during 2 World War girls didn’t get periods until 16 III. studies of peace time also demonstrate role of nutrition in growth a. Bogota, Columbia i. provision of food supplements for the whole family from mid-pregnancy until 3 years old prevented severe growth retardation in children at risk for malnutrition ii. Remained taller and heavier at 6 years old than control children b. Rural Bangladesh i. changing traditional unhygienic practices with educational interventions improved children’s health, growth, and nutrition ii. Safer methods of food preparation = less food contamination, reduced incidence of diarrhea which interferes with the absorption of essential minerals and vitamins c. iron-deficiency anemia: i. disorder in which inadequate amounts of iron in the diet causes listlessness and may retard children’s physical and intellectual development ii. common among poor minority children and children in low-income countries especially those w/ low amounts of meat in diet iii. Kenya and Zanzibar: iron or meat supplements found to improve children’s rates of growth and motor + mental development C ATCH ­U P G ROWTH I. Tendency for human beings to regain a normal course of physical growth after injury or deprivation a. Degree of catch up growth that can be achieved depends on duration, severity, and timing of original deprivation and nature of treatment II. Studies a. Malnourished infants who had 5% deficit in height and weight were able to catch up but those with 15% deficit remained shorter b. 20 year longitudinal study of starved children: nutritional program failed to enable full dev in head circumference (and presumably brain dev) i. Effect of malnutrition on brain dev may account for intellectual and attentional deficits shown by malnourished children III. Timing a. Undernourishment early in life = serious consequences b. Children starved in utero = partial catch up c. The earlier and more prolonged the malnutrition, the more dif it is to achieve normal growth PEOPLE ARE GROWING TALLER th th I. b/w 11 and 14 century the avg British male was 5’6; now it’s 5’9 a. shows a secular trend: a shift that occurs in the normative pattern of a particular characteristic over some historical time period II. differences in socio-economic status a. North Americans = upper 75% reached maximum growth b. Less advantaged segments of society = continue to grow III. Feet are growing as well IV. People now reach adult height at 16-17 instead of 20s like in the past V. Reasons a. Health and nutrition has improved i. Growth retarding illnesses are under control ii. nutritional intake has improved in terms of quantity consumed and balance among essential food groups iii. medical care and personal health practices improved b. Socio-economic conditions have improved i. Child labour less common ii. Living conditions and sanitation improved c. Influence of genetic factors affected by intermarriage among people of dif backgrounds i. Produces increases in height of offspring ARE WE GROWING HEAVIER? OBESITY AND EATING DISORDERS I. Obesity: condition in which a person’s weight is 30% or more in excess of the average weight for his or her height and frame II. Early 1960s – 5% of children were overweight, 2004 = 18% of children were obese W HY  DO  CHILDREN  G AIN  TOO  M UCH  W EIGHT ? I. Level of caloric intake combined with a growing trend toward physical inactivity a. 62% of Canadians are relatively inactive II. Genetic factors a. Risk for obesity was greater among first degree relatives than spouses b. Identical twins are twice as likely to resemble each other in weight as fraternal twins c. Studies of early infant behaviour i. Newborn infants w/ two overweight parents were more responsive to a sweet tasting solution than plain water than infants of normal weight parents ii. Babies’ genetically determined sucking patterns predict later obesity iii. Children who are overweight tend to stay that way III. Education and income a. National health survey found that as income increases there’s a decreasing likelihood that excess weight constitutes a health risk b. Chances of being overweight decreases with education i. Canadians w/ less than a high school education are about one and a half times more likely to face problems due to being overweight than university graduates IV. Modelling by others affects children’s eating behaviours a. Parents of obese children encourage them to eat more than their thinner siblings b. Rewarding children for eating everything on the plate may teach them to rely on external instead of internal cues in deciding whether to eat i. Eating when food is in sight instead of when you’re hungry V. Obese individuals suffer from many physical problems a. Asthma b. Sleep problems c. Hypertension d. Diabetes e. Risk of high cholesterol levels VI. Also suffer from psychological problems a. Body image disturbances b. Discrimination by thinner peers VII. Overweight adolescents date less and are less likely to be admitted to prestigious colleges T REATING  O VERWEIGHT  CHILDREN I. It appears to be important to involve the family in any treatment program a. Parents often encourage overeating b. Reducing the likelihood of stressful interactions with family members at mealtime can help curb overeating c. School based peer tutoring programs show promise as an obesity prevention strategy (teaching lessons about healthy living) II. Increasing the physical expenditure of energy in innovative ways a. Making small lifestyle changes like walking an additional 2000 steps a day and reducing calorie intake by replacing sugar with non-caloric sweeteners b. Study i. Choice may be important in getting children to increase level of exercise ii. Letting kids ride bikes or skate instead of forcing them to do specific exercises E ATING  DISORDERS  IN A DOLESCENCE I. Afflict more women than men II. Generally strike b/w 10 and early 20s III. More prevalent in industrialized societies IV. May exhibit symptoms of depression V. Often come from families with histories of eating disorders or substance abuse VI. Linked to images prevalent in the media VII. Anorexia nervosa: a disorder in which a person is preoccupied with avoiding obesity and often diets to the point of starvation a. see themselves as obese despite being slender b. eat little, although may be preoccupied with food and even hoard it c. may lose up to 25% of body weight and become so weak that hospitalization is required to correct electrolyte imbalances d. may begin at various points in life, especially in puberty e. affects 1% of young women f. become socially withdrawn g. tendency toward obsessive-compulsiveness (recurrent obsessions or compulsions to do certain things), perfectionism, and a strong need to control the environment i. controlling food intake is the only way the feel they can exert control over their lives h. families often high achieving and protective i. overbearing mothers and ‘emotionally absent’ fathers i. treatment: i. may require initial hospitalization and physical intervention ii. longer term psychotherapy including the family has led to some success iii. fewer than half make a complete recovery iv. 5-10% die from starvation or suicide VIII. bulimia nervosa: alternate periods of binging with vomiting and other means of compensating for the weight gained a. cycles of uncontrollable binge eating followed by either vomiting or the use of laxatives to compensate for bingeing to prevent weight gain b. sometimes seen in women pursuing activities that stress slimness like gymnastics and ballet c. risk fluid and electrolyte abnormalities, loss of stomach acid, frequent induction of diarrhea can cause metabolic problems d. most causes emerge during late teens and early twenties e. affects 1-3% of young women f. rarely diet to point of starvation g. typically extraverted and have poor self-images h. families often chaotic, conflict ridden and stressed, f
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