Notes From Developmental Psychology Lecture

It used to be thought that you were born with all of the neurons that you would have the rest of your life. Researchers tended to extrapolate from this that the brain and the NS in general was relatively unresponsive to the environment. This is wrong. Research over the past 20 years has suggested that the development of the brain is remarkably influenced by the environment.

Moreover, recent research has demonstrated that your brain actually is growing new neurons all the time. Nottebohm's research on neurogenesis (creation of new neurons) in songbirds (e.g., free-ranging chickadees have twice the neurons in the area of the brain associated with songs, compared to caged chickadees--and this is directly related to their repertoire of songs. Explanation: environmental pressures requiring a greater range of communication in free-ranging songbirds leads the brain to make more neurons to increase the repertoire of songs. In humans neurogenesis has been demonstrated. A large quantity of neurons are created everyday (in the lining of the ventricles), which then migrate both to the hippocampus and to various areas of the cerebral cortex itself--areas associated with higher brain functions. This work, published in Science in 1999, by Liz Gould, Charlie Gross, and colleagues at Princeton is groundbreaking because all neuronal theories of learning and memory (how and where are memories stored in the central nervous system?) are based on changes at the synapse (Myers pp.330-1). Gould et al. suggest that synaptic changes might not be the full story--that perhaps introducing new neurons may also be involved in learning/memory. If you are interested, check out the Princeton press release describing this research

Rosenzweig: Experiments with rats. Baby rats randomly assigned to two conditions:

• Impoverished environment--Plain cages in a dimly illuminated, quiet room; nothing to do

• Rich environment--running wheels, ladders, slides, and "toys" Change toys everyday to ensure that they learn as much as possible.

1. Thicker cortex, better capillary supply, more glial cells, more protein content, more ACH (important since ACH has been implicated in memory--remember Alzheimer's Disease-->cholinergic (ACH) neurons die).

2. More dendrites in the cortex; more dendritic branching, more increases in area of contact at the synapses.

Greenough: The beneficial effects of rich environment also happens with middle-aged rats and elderly rats. 2,000 additional synapses per neuron compared to control rats. Extrapolates to trillions of new connections.

Effects of handling--even handling rats once a day dramatically increases performance on a maze, and leads to beneficial physiological effects on the brain.

Conclusion: Plasticity of the brain: the brain is very responsive to the environment. Stimulation-->positive effects. But if the brain is exposed to a negative environment-->negative effects. One example: fetal alcohol syndrome.

Videotape on Teratogens and Their Effects on the Developing Brain and Mind (#12--12:44)

• Neurons and glial cells work together: glial cells find the neurons and help them migrate to their proper places in the brain.
• Teratogens--substances that, when present in the growing fetus, create damage in the developing brain.
• First example: radiation leak at Chernobyl: led to a 5-fold increase in the rate of mental retardation
• Hiroshima and Nagaski: atomic bomb radiation led to problems in brain development. Children exposed to radiation in utero (in the womb) were severely affected.
  • There were differences in the extent of the effects of radiation on the child depending on what stage in fetal development the exposure occurred. Specifically--the greatest damage occurred when the neurons were migrating (8-16 weeks after conception). In fact, 80% of the mental retardation cases in Hiroshima and Nagaski are due to exposure during that critical period. The radiation caused the migrating neurons to stop short of their final destination; thus, those neurons could not perform their programmed function because they weren't where they should have been.

• Second example of a teratogen: alcohol during pregnancy. Fetal alcohol syndrome (FAS)--mental retardation, hyperactivity, short attention span, and a variety of other cognitive and behavioral difficulties.
  • Gyri--convolutions of the cortex
  • Ventricles--holes in the brain. Ventricles are much larger in FAS infants. Less white matter.
• Brain cells migrate to various places in the brain. FAS: disrupts the migration. Cells don't migrate to where they should be going. This is called heterotopias: brain cells in the wrong place. The videotape suggests that radiation exposure causes the migration process to stop short and that alcohol causes the migration to run wild, with neurons going past their destination.
• How much does it take to damage the brain? The classification of FAS=heavy use of alcohol--alcoholic mother. But there are studies suggesting that children of moderate drinkers (1-2 drinks/day) are affected: they were less attentive and alert, and the effects were still present at four years of age (Streissguth et al., 1984).

Infant Sensation and Perception

• Sensation: Information about external events is detected by the sensory receptors and transmitted to the brain. Babies can sense the environment. Newborns turn their head toward sounds. React to brightness, they respond to pain.
• Perception: Interpreting the sensory input by the brain. Can newborns interpret or understand the sensory information that her receptors detect?

• Long before anyone began to conduct experiments on sensation and perception, philosophers debated whether newborns could perceive. Two diametrically opposed positions:
  • Empiricists: Locke (1690)--infants are tabula rasa (blank slate). They must learn how to interpret their sensory experiences. James (1890)--"To the infant, sounds, sights, touches, and pains, form one unanalyzed blooming, buzzing confusion." James believed that the senses are all jumbled up and indistinguishable at birth. Over time, the infant discriminates different senses.
  • Nativists: Descartes--innate ideas. The major perceptual abilities are already present at birth. Kant (1780)--spatial perception is innate. Apparent size, etc. Already hardwired. Example: Mikey in Look Who's Talking.
• Of course, the debate isn't this extreme today--somewhere in the middle. There are indeed some abilities that are apparent in newborns. In fact, it really is surprising just how much infants can do. It used to be the case that the newborn was seen as a brainstem until 3 months of age.
• But there is a basic problem--how can we tell how well an infant can see or hear? How can we tell whether they can taste, smell, or tell the difference between red and blue? Research methods to study infant perception:

Preference Method

1. Present at least two stimuli simultaneously. See whether infants attend more to one of them.

2. Early 60's after Fantz used it to determine whether very young infants could discriminate visual patterns (faces, concentric circles, newsprint, unpatterned disks)

Method:

1. Babies placed on their backs in a looking chamber. Shown two or more stimuli
2. Observer located above records the amount of time infant gazes at each of the stimuli
3. Looking longer at one than the other: assumption--prefer that stimulus.

Fantz's results:

1. Babies less than 2 days old could easily discriminate visual forms.
2. They prefer to look at patterns (faces, concentric circles) rather than unpatterned disks.

Preference studies still conducted today.

Interpretation problem: If you get a difference, everything's OK. Can be interpreted--infant can discriminate. But suppose no preference is indicated. Interpretation isn't clear. Two possibilities:

1. Maybe infant cannot discriminate yet.
2. But maybe the infant can discriminate, but finds the two to be equally interesting.

Habituation Method

1. Most popular method
2. Habituation: Introduce a new stimulus--infant responds (head/eye movements, heart rate, respiration, etc.). But as you repeat the stimulus, the responses go away. Habituation is a simple form of learning. As infant stops responding, it is indicating that it's old hat.
3. Not just true of babies. We also show habituation effects. Even though we may can smell our own perfume when we first apply it, after awhile, we adapt to the stimulus. Don't even smell it after awhile.

1. Present first stimulus until the infant habituates (that is, the infant's reactions, e.g., heartrate, etc. return to baseline.
2. Now present the second stimulus. If infant discriminates the two, then she will indicate by attending closely, or change in respiration/heart rate, etc. If infant fails to discriminate--no such changes will occur (no responding).
3. Good method because babies habituate to so many different kinds of stimulation.

1. Electrical recording of the brain
2. Present stimuli--see how brain activity in particular locations is changed. e.g., visual stimuli--occipital; auditory stimuli--temporal
3. If infant detects the stimulus, change in the pattern of brain waves-- evoked potential.
4. For two stimuli that are sensed differently--different patterns of electrical activity

High-Amplitude Sucking (A Kind of Habituation Method)

1. Developed in the late 1960's
2. Special pacifer with electrical circuitry that allows the infants some control over their environment.

Method

1. Establish baseline sucking
2. Whenever sucking harder or faster than baseline (high-amplitude sucking), activates slide projector or tape recorder--present stimuli
3. If infant finds it interesting--will continue to suck more than baseline for as long as he/she is interested
4. When not interested--habituation occurs--sucking goes back to baseline
5. If you now introduce another stimulus--if the infant can tell the difference, then sucking will go up; if the infant can't tell the difference, sucking remains at baseline
6. Can modify to let the infant tell us which of two stimuli she prefers