Psychology of InfancyDefining development, prenatal development, brain development D. Messinger, Ph.D.
Questions (single essay format) • Define development. Argue for why you believe development does or does not have an endpoint. • Describe genetic and experiential factors in brain development referring to experience expectant and experience dependent factors. • Give examples of how prenatal sensory experience impacts sensory development. • Is it is all over after age 3? • Provide examples from Nelson. • What are some basic patterns of synaptic and brain development in infancy? • How they are influenced by experience? • What can go wrong in this pattern?
Development defined • Individual change that is, normative, non-reversible, relatively stable, and sequential. • Normative process • Everyone’s doing it • Non-reversible • Reorganization of the entire person • Relatively stable • You can’t go back, • Sequential change • Crawl before you walk • Examples
Is development • Increasing functionality in all things? • Loss of perceptual acuity in non-native languages between 6 & 12 months • Old-age
Is development • Headed toward a goal? • Development has normative outcomes, • but time goes forward • prior events cause subsequent events • not the opposite • What does Thompson (2001, p. 21) mean? • “A drive to development is inborn, propelling the human infant toward learning and mastery.”
Three models In class assignment: What would a cross-tab of the transactional model look like?
What does individual development look like? Individuals Group
Overview • Increasing differentiation of areas of cortex • Infant is born during height of brain development • Tertiary sulci develop from 1 month before to 12 months after birth
Four levels of brain development From Nelson, 1999
Proliferation & migration of neurons • General pattern of brain development genetically specified • By 20 weeks, most neurons present • 3rd - 16th prenatal week most crucial • At 8 weeks, head is half of fetus • But specific connections depend on generic growth processes and sensory-motor stimulation • Trillions of connections still forming • Trimming of these connections is developmental task
Neural migration • Many elements of initial neural migration specified genetically • By 20 weeks gestation, 100 billion neurons! • 50,000 – 500,000 neurons per minute • Neurons follow path of glial cells outward from ventricles • To form 6 layers of cortex
Neural development: Synaptogensis • Once in place, synapses are overproduced somewhat haphazardly • 1 year old has 150% more synapses than adult • These are pruned (diminish) during development • Repetition of sensory-motor patterns create more specific set of experience dependent synaptic linkages
Time lapse sequences of radial migration (also known as glial guidance) and somal translocation neurite outgrowthhttp://www.youtube.com/watch?v=n_9YTeEHp1E&NR=1 Typical and Atypical http://www.youtube.com/watch?v=GBIa8G3gBH0&feature=related
Increase in complexity of neural connections Like a growing forest
How do the correct synapses form? • 15,000 synapses for every cortical neuron • 1.8 million per second in first 2 years! • Cerebral cortex triples in thickness in 1st year • Sensory and motor neurons must extend to correct brain are and form correct synapses • This quantity of information cannot be genetically micro-managed
Experience-expectant Experience dependent Two types of experience in brain development
Experience-expectant • “How common early experiences provide essential catalysts for normal brain development” • Early visual stimulation, hearing, exposure to language, coordinating vision and movement, • “The developing brain “expects” and requires these typical human experiences, and relies on them as a component of its growth.”
Experience-dependent • “How individual experience fosters new brain growth and refines existing brain structures” • “Can be unique to an individual” • Reading • Singing, music
Neural Darwinism (Edelman) • Use it or lose it • What is not used, is pruned • What is used, develops stronger connections • Organism & environment are system that shapes brain • Brain development is guided by environment • Brain enables behavior which shapes brain • Synaptic development is not teleological
The fetus as constructing its own development • Fetal behavior impacts physical development • In chicks prevented from moving, cartilage turns to bone • Fetal sensory experience impacts sensory development • Mice whose tongues were anesthetized had malformed cleft palates
Prenatal sensory experience impacts sensory development • Hearing typically develops before sight • Rats, ducklings, and quail chicks exposed to visual stimulation prenatally • before they normally would • lose hearing ability at birth
Normal sensory development contingent on extra-fetal environment • Differences in the timing of augmented prenatal stimulation led to different patterns of subsequent auditory and visual responsiveness following hatching. • No effect on normal visual responsiveness to species-typical maternal cues was found when exposure to tactile and vestibular stimulation coincided with the emergence of visual function (Days 14-19) • When exposure took place after the onset of visual functioning (Days 17-22), chicks displayed enhanced responsiveness to the same maternal visual cues. • When augmented tactile and vestibular stimulation coincided with the onset of auditory function (Days 9-14), embryos subsequently failed to learn a species-typical maternal call prior to hatching. • Honeycutt, H. & R. Lickliter (2003). Developmental Psychobiology43: 71-81. The influence of prenatal tactile and vestibular stimulation and visual responsiveness in bobwhite quail: A matter of timing
Prenatal behavioral development • 9 weeks - movement • 16 weeks - frowning, grimacing • 25 weeks - moves to drumbeat • 26 weeks - remembers sounds • 32 weeks - all brain areas functioning • 34 weeks - can habituate
Overview of brain growth • Subcortical areas responsible for reflexes develop first • E.g. spinal cord • Followed by cortical areas in a specific progression • What is most human develops last • Most but not all neurons present at birth • Synapses develop • Myelin develops
At the same time - Myelinization • Fatty sheaths develop and insulate neurons • Dramatically speeding up neural conduction • Allowing neural control of body • General increase in first 3 years is likely related to speedier motor and cognitive functioning • allowing activities like standing and walking • Endangered by prenatal lead exposure
“Promoting early brain development”? • Re-discovery of importance of early experience • “How brain connections grow and change as a result of stimuli from the environment. • How early stress can be harmful to the developing brain. • Principle of "use it or lose it" • Seven ways to support brain development: • http://www.pitc.org/
“Considerable misunderstanding of early brain development occurs when neurons and synapses are considered independently of the development of thinking, feeling, and relating to others.” Thompson, 2001, p. 29
Is it all over after 3? • Is the course of development set in infancy? • Early experience is important • But, with some exceptions, human beings remain open to the positive effects of additional experience • The same is true for the impact of experience on brain development • How important is it to ‘stimulate your child’s brain’?
What does Nelson say • Acrobatic rats (p. 423)… • Adult neurogenesis …
Implications for practice • It is important to provide a safe, warm, supportive, stimulating environment for infants • But its never too late to improve developmental outcome for an individual • At any point, current conditions are as important as past conditions • No flashcards
Brain Overgrowth in the First Year of Life in Autism • The clinical onset of autism appears to be preceded by 2 phases of brain growth abnormality: a reduced head size at birth and a sudden and excessive increase in head size between 1 to 2 months and 6 to 14 months. Abnormally accelerated rate of growth may serve as an early warning signal of risk for autism • Courchesne, Carper, Akshoomoff, (2003) • Why overgrowth?
Nelson • Later developing processes more susceptible to the effects of experience • Motor development more plastic than language development • Sensitive periods • Genetics and experience: Indissoluble
Birth Process Midwifery – the first profession
Human birth – cephalo-pelvic proportionality Are human beings evolving? How might the rise in the rate of delivery by c-section be related to evolution?
Human birth – a social process "In nonhuman primates, the fetus usually emerges with its face toward that of its mother. She may then reach down and pull it up toward her along the normal flexion of its body. "In humans, however … the close equivalence of cephalopelvic dimensions has resulted in … infant being born facing away from its mother. In this position, the use of her own hands to assist delivery before the shoulders have emerged could result in pulling the infant against the normal flexion of its body, again with the risk of injury particularly to the nerves of the neck." Wenda R. Trevathan, Human Birth, (New York: Aldine de Gruyter, 1987), p. 89-92
Final project ideas • Prenatal maternal stress • Prenatal behavior • Impact on outcomes (after birth)
Human birth – graphic content • More medical, ‘produced’ video • http://video.google.com/videoplay?docid=-7170052415220169972&q=birth+videos • Just video of birth • evtv.com • NPR segment on birth process