The Long Shadow of Temperament is a book by Dr. Jerome Kagan (a psychology professor at Harvard) and Dr. Nancy Snidman (Director of the Child Development Unit at Children’s Hospital Boston). The book describes the results of a longitudinal study that indicates infant temperament is heritable and stable throughout childhood and into adulthood.
This post has some notes from the book.
• A study of middle-class men in California found that those who were shy as children established their careers, chose wives, and became fathers later in life than their more sociable peers.
• Eighteen-year-olds in New Zealand who had been categorized by observers as shy when they were 3 years old described themselves as cautious when facing new challenges or dangerous situations.
• A study of children over nearly 30 years found that a small group of children who usually avoided unfamiliar people, objects, and events during the first 3 years preserved some derivatives of that bias as young adults. They were introverted, cautious, and dependent for emotional support on family, friends, or spouses. By contrast, the bolder, sociable children were extroverts who chose competitive, entrepreneurial vocations. The adults who had been the timid children had high, minimally variable heart rates, suggesting higher sympathetic tone in the cardiovascular system.
• A study of children who were assessed at ages 4, 5, 7, and 13 found that children classified originally as inhibited retained an inhibited behavioral style, while children who had been classified as uninhibited preserved a bold, sociable profile. The children were evaluated again when they were between 12 and 14 years old. Those who had been inhibited were more likely to show signs of social anxiety.
• A study of children who were 4.5 years old found that twice as many low-reactive as high-reactive children were extremely sociable and talkative during a play session with unfamiliar children. By contrast, 46 percent of those who had been high-reactive infants were shy, quiet, and timid, compared with only 10 percent of those who had been low-reactive infants.
• 7-year-olds who had been high-reactive infants were most likely to have anxious symptoms. 45 percent of high-reactives but only 15 percent of low-reactives received this classification.
• The high-reactives displayed fewer spontaneous comments and smiles while interacting with the examiner.
• The low-reactives were more likely than high-reactives to report they were “happy most of the time.”
• The biological measures regarded as indirect signs of amygdalar excitability were more frequent among the 11-year-olds who had been high-reactive infants than among those who had been low-reactive.
• A slightly shorter stature, lighter weight, and blue eyes were more common among the high-reactives, while more low-reactives were taller, heavier, and more often brown-eyed.
• When teachers in 133 different classrooms nominated the Caucasian child in thier class who was most shy and the Caucasian child who was least shy, 60 percent of the most shy children were blue-eyed and 58 percent of the least shy children were brown-eyed.
• A study found that 10 girls born to a parent with panic disorder were extremely shy with the examiner and had a very high heart rate – and all 10 girls had very light blue eyes.
• The fact that more than twice as many high-reactives as low-reactives had values on some of the physiological variables that imply an excitable amygdala, whether these adolescents were shy or bold, implies preservation of a biological property over the course of childhood.
• Very few high-reactives became exuberant, sociable, minimally aroused preadolescents, and very few low-reactives became fearful, quiet introverts with high levels of biological arousal. Less than 5 percent of the children from each of these temperamental groups developed the behavioral and biological features characteristic of the other type.
• When teachers in kindergarten and, later, in sixth grade rated over 1,800 Canadian children for fearfulness, most of the sixth-graders received a rating that resembled the one they had received in kindergarten.
• A study found that shy and over-controlled Icelandic children were more likely than their classmates to remain shy at adolescence.
• A study found that two-year-old children who were described by their adoptive Dutch mothers as shy and dysphoric possessed similar traits when they were 7 years old. Neither the family’s social class nor the mother’s sensitivity with her infant predicted these psychological properties at 7 years.
• A group of fourth-grade and fifth-grade children living in south Florida had been assessed for the presence of anxiety 15 months before Hurricane Andrew struck the area. The 11 percent of the children who remained distressed 7 months after the fierce storm had been categorized as anxious prior to the hurricane.
• A study found that only 10 percent of a sample of 2-year-olds were consistently inhibited across varied unfamiliar events, and only the consistently inhibited children had low vagal tone.
• The degree of amygdalar activation is correlated primarily with the magnitude of discrepancy or degree of unexpectedness of an event, rather than with its degree of danger or level of aversiveness.
• Estimates of the heirtability of panic disorder range between 0.5 and 0.6
• The heritability of smiling and laughter in a large sample of monozygotic and dizygotic twin pairs approached 0.6, which is higher than the heritability of behavioral inhibition.
• Adult extroverts have more power in the alpha frequency band in frontal areas in EEG studies than introverts, and this frequency band increases in power from 6 to 11 years of age.
• Individuals with greater activation in the left frontal area of the brain more often report sanguine moods, are biased to detect pleasant features in pairs of words, and show less anxiety than the smaller portion who show greater activation on the right side.
• Social phobics showed increased activity in the right dorsolateral prefrontal cortex when they thought they had to give a short speech while strangers watched.
• Four-year-olds who were shy with 3 other unfamiliar children in a laboratory playroom showed right frontal activation, while those who were sociable showed left frontal activation. A similar result was found in 9-year-olds.
• Adults who reported being shy and minimally sociable showed right frontal activation, while extroverts, with the opposite persona, showed left frontal activation.
• Perhaps the most intriguing relation between the child’s self-reports and asymmetry involved the item “I feel really bad if one of my parents said I did something wrong.” Every high-reactive boy who was right-active at frontal and parietal sites ranked this item as more descriptive than the total sample, compared with only one-third of the high-reactive boys who were left active at both sites.
• Only 23 percent of right-active, high-reactive boys endorsed the item “I enjoy going on roller coasters in amusement parks,” compared with 67 percent of left-active, high-reactive boys.
• 47 percent of low-reactives, but only 15 percent of high-reactives, combined a preference for novelty with low biological arousal.
• When low-reactive children reported a preference for novelty, the probability was 0.8 that they would show low biological arousal. When high-reactive children disliked novelty, the probability was 0.8 that they would show high biological arousal.
• A longitudinal study of British children reported that the children who preserved their inhibited behavioral style from 4.5 to 7.5 years of age had higher heart rates than others.
• Asian and Caucasian populations differ in a DNA segment that defines the promoter region monitoring the production of the serotonin transporter molecule and in alleles that affect the receptors for gastrin-releasing peptide. This peptide mutes activity in the basolateral nucleus of the amygdala by enhancing GABA activity.
• Clinicians have learned that Asian-American psychiatric patients require a lower dose of psychotropic drugs than Caucasian-American patients with the same symptoms living in the same region, implying that Asians are at a lower level of limbic arousal.
