Are critical periods critical for early childhood education? The notion of a window of opportunity opening in early childhood, and then closing, never to open again, evoked a powerful visual image in the mid-1990s. It galvanized scientific and popular media to attend to the problems of early childhood education. lectures notes for developmental psychology, ps241, 2004, prof catherine l harris, boston university

Newsweek cover story in 1996 But they imply, too, that if you miss the window you're playing with a handicap. They offer an explanation of why the gains a toddler makes in Head Start are often so evanescent this intensive instruction begins too late to fundamentally rewire the brain. -- Newsweek, February 19, 1996

From animal research Hubel and Wiesel (1970), suturing shut the eye of a kitten The ducklings raised by Konrad Lorenz imprinted on first moving object (recent film, Fly Away Home)

Understanding the programmatic nature of early brain development Born with all (cortical) neurons you will have, neurons die at furious pace in first years of life (apoptosis: programmed cell death) Neurons that fire together, wire together Identifiable waves of synaptogenesis, followed by pruning of connections

Neurons that don't connect, die

What happens to animals raised in complex environments? Greenough's research: rats reared in enriched environments had more dendritic branching "Revelation" for Caregivers: that they could engage in activities that would influence their child's brain development Are the effects of complex environments “critical period” effects? Do we think that same kind of neural processes underlie both kinds of effects?

Synaptic Density: Infancy to Adulthood

More factors that raised awareness Deleterious effects of prenatal teratogens (alcohol, cocaine), and early childhood exposure to lead Early childhood risk factors: poverty, nutritional deprivation, social neglect, maternal depression, childhood abuse, multiple risk factors neglect (Romanian orphanages)

Summary of Ideas from Neuroscience Synaptogenesis -- in infancy the brain forms synapses in excess of adult levels. Critical periods -- normal development of neural systems requires specific experiential input at specific times. Pruning at Puberty -- at sexual maturity synapses are pruned back to adult levels. Enriched environments increase synaptic connections.

Two Categories of Human Abilities Our brain underwent evolved under the pressure of natural selection to have some abilities. basic vision, first language learning, categorization, number sense, time sense, deception, social relations Our brains didn't evolve to manifest: writing, algebra, astronomical understanding, breeding of animals, etc.

Environmental input necessary for these abilities are those that the brain could expect to encounter. If they are not present, brain development proceeds abnormally, and critical period effects can occur. .

No special areas of the brain evolved to support writing, algebra, etc. When these abilities develop, they generally recruit specific areas of the brain. BUT: Brain development depends on the exposure to the relevant concepts. If this experience doesn't occur, brain development is not abnormal. Brain development is normal, because the brain doesn't *expect* these inputs. The hypothesis here is that critical period effects will not occur for these "experience-dependent" activities. All of education is about experience-dependent behavior.

Side note: Controversial whether these “evolved” second language acquisition art, music, dance, religion, story telling abstract "patterning" (cf. Gardner) warfare, infanticide, genocide,

“Critical Period” for Music? In the brains of nine string players examined with magnetic resonance imaging, the amount of somatosensory cortex dedicated to the thumb and fifth finger of the left hand -- the fingering digits -- was significantly larger than in nonplayers. How long the players practiced each day did not affect the cortical map. But … the younger the child when she took up an instrument, the more cortex she devoted to playing it. -- Newsweek, February 19, 1966

Did not control for duration or practice effect

John Bruer, Myth of the First Three Years ,1999 and other authors: Critical periods are the exception rather than the rule Adults can learn to read or can learn a new language Do critical periods exist for providing an organism with a higher-quality experience? Recent neurobiological work: life-long plasticity; neural reorganization after brain injury Wide variability in human performance for non-evolutionary, "higher cognition"

Rationale for early childhood initiatives What are “Sensitive periods”? Windows for learning open at birth The first years are foundational Early childhood enrichment can compensate for social deprivation Shift attention away from critical periods to critical experiences Teachable moments; transitions, crises