Sept 271.ppt - Prenatal Brain Development Brain constructs itself from the inside out Brain growth reflects neuronal proliferation production of neurons

Sept 271.ppt - Prenatal Brain Development Brain constructs...

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Unformatted text preview: Prenatal Brain Development Brain constructs itself from the inside out Brain growth reflects neuronal proliferation production of neurons begins about 10 weeks after conception Complete at 28 weeks 250,000 new neurons every minute in embryonic period Growth also reflects development of glial cells As the brain develops, neurons migrate from the inner surface to form the outer layers. Left: Immature neurons use fibers from cells called glia as highways to carry them to their destinations. Right: A single neuron, shown about 2,500 times its actual size, moves on a glial fiber. Brain Development At birth an infant’s brain has: •A lot more neurons than an adult •A lot fewer synapses than an adult •12-month-old has 150% more synapses than the adult ‘Neural Darwinism’ brain is programmed to create more nerve cells and more connections between these cells than are needed neuronal death synaptic pruning Provides more space Refining internal circuitry Experience-expectant growth Fall, 2005 How Do Young Brains Get Hooked Up? • Greenough (1980s): Brain development is an extended process strongly influenced by postnatal experience • Specific experiences produce neural activity that in turn determine which of the excess synapses will survive – Nervous system prepared by evolution to expect certain types of stimulation (e.g., patterned light, moving objects) – These experiences form and maintain synapses • Experience-expectant processes – Certain functions (e.g., visual acuity) will develop for those who have the experience – if not, the connections are pruned Fall, 2005 How Do Young Brains Get Hooked Up? Maurer et al. studied infants who were born with cataracts and had them removed at different points in life. Those who had the cataracts removed within the first several months after birth displayed the typical pattern of visual development. Those who had the cataract removed later showed poor visual development, and poor face processing. Blakemore, C., and Cooper, G. F. (1970). Development of the brain depends on the visual environment. Nature , 228:477-478 The result is that the “vertical” cells multiply, while the “horizontal” cells shrink and degenerate Horizontallyreared Verticallyreared Apoptosis (cell suicide) death is preprogrammed for the cells that disappear from the hand plates Syndactyly Human Brain Development Synapse Formation Dependent on Early Experiences Language Sensory Pathways (Vision, Hearing) Higher Cognitive Function FIRST YEAR -8 -7 -6 -5 -4 -3 -2 -1 1 2 3 4 5 6 7 8 9 10 11 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Birth (Months) (Years) “Critical Periods” in Brain Development Are there “optimal environments” for brain development? Rats raised in stimulating environments develop 25% more synapses than rats who are raised with little stimulation (Greenough, Black, & Wallace, 1987); There is no evidence that shows that intensive enriching experiences in the early years enhances brain power through the lifespan (Bruer, 1999; Thompson & Nelson, 2001). California obstetrician named Rene Van de Carr founded a "Prenatal University“ with a curriculum that started four months before birth ‘First Years Last Forever’ ?????? ?????? out of 65 families surveyed, 97 percent owned a touch screen device average age of a child starting to use a touch-screen device was about 11 months Christakis et al (2004) found the more television children watched before the age of three, the more likely they were to have attention problems at school compared to those who watched none "Some have advocated providing extremely enriched environments, full of bells, whistles, moving objects and so on for human infants. Actually there is no evidence at all that such "super rich" environments have any effect on the development of normally raised human infants. The normal environment provided by caring parents or other caregivers seems quite sufficient. On the other hand, tragic situations where human infants are left alone in cribs except for feeding and changing do result in substantially retarded development.” (Thompson, 2000) Play with electronic toys is associated with decreased quantity and quality of language input compared with play with books or traditional toys. To promote early language development, play with electronic toys should be discouraged. Traditional toys may be a valuable alternative for parent-infant play time if book reading is not a preferred activity Sosa AV.Association of the type of toy used during play with the quantity and quality of parent-infant communication. JAMA Pediatr 2016 Feb 1; 170:132. Attention One way of investigating perception in very young infants is to look at the orienting response An indication of attention and learning Decrease in the orienting reaction is termed habituation Found in 27- to 36-week-old fetuses and 1-day-old newborns • Listened to a word, turned head toward sound, heard same or different word next day How do we know that an infant is not merely fatigued when he stops responding to a familiar stimulus? dishabituation or recovery of attention indicates ability to distinguish familiar from the unfamiliar Sensory receptors are not simply fatigued habituation improves dramatically throughout the first year Under 4 mos, may require long exposure to a stimulus b/t 5 and 12 mos, after a few seconds Newborn Taste Abilities Newborns discriminate the four basic flavors of Sweet, Sour, Bitter, Salty Newborns prefer sweet and salty Most infants seem to have a “sweet tooth”. Infants will nurse more after their mother has consumed a sweet-tasting substance like vanilla (Menalla, 1997) Newborns prefer sweet. However, at 4 months, infants will have a salty preference They will start liking salt which was aversive to them as newborns. Sensory and Perceptual Capacities ...
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