Jerome Kagan and Nancy Snidman made a great attempt at finding a solid and agreeable definition of temperament. In order to prove or disprove their hypothesis, “that most temperamental biases are due to heritable variation in neurochemistry or anatomy, although some could be the result of prenatal events that are not strictly genetic,” Kagan and Snidman performed a number of ethical studies on children’s reactions to certain objects, people and environments. They did additional studies on rats, as well. These studies included: EEG power and asymmetry of activation, brain stem auditory-evoked potential, balance between sympathetic and vagal reactivity in the cardiovascular system, event-related potentials, startle and corrugator activity, and anthropometry. In completing these studies, Kagan and Snidman were able to prove or disprove their hypothesis.
Kagan and Snidman went about trying to prove their hypothesis by conducting ethical studies and observations on children. The first study was the EEG power and asymmetry of activation study. The EEG study was actually more of an observation. This observation allowed Kagan and Snidman to be able to categorize children based upon their temperament. These observations included the reactions of children in the dark or in situations where strangers would approach them. More specifically, during the bombing London during World War II, British children younger than five years old who became fearful after being taken from their homes were shown to have been highly fearful before the bombing occurred. Children such as those in London during World War II have been proven to have more activity in the relative right frontal electroencephalogram (EEG), which is what actually categorizes them as inhibited or shy. Children who exhibit opposite behavior have been proven to have more activity in the relative left frontal EEG, which is what classifies them as uninhibited or social and outgoing.
These observations did not prove that the temperaments were based on biology or that they were heritable, however, they did verify that these temperaments were demonstrated early in life and remained the same over time. Children who were highly fearful at two years of age, preserved an inhibited persona through the age of eleven. The observations also illuminated the fact that parental behavior had an effect on the children’s temperament. Inhibited two year olds with intrusive, hypercritical mothers were more likely to preserve their shy behaviors than those with less intrusive mothers. This factor also disproves the hypothesis that temperaments are inherited, but verifies that temperaments are learned.
Studies were also conducted on brain stem auditory-evoked potential. Variation in the magnitude of Wave 5 in the brain stem auditory-evoked potential differentiates among the temperamental and personality classifications. Introverts, or inhibited people, have the tendency to peak in Wave 5 before extroverts,...