Behavioral Inhibition as a Temperamental Category
Authors: Kagan Jerome 
Published: November 2023

Abstract
Historical changes in the sense meaning of the term temperament have been less dramatic than alterations in other important psychological concepts, such as emotion, memory, symptom, or perception. Most ancient and modern writers agreed that the human temperaments were combinations of psychological profiles (behaviors, thoughts, and emotions) and their presumed biological foundations, which, during this century, were assumed to be genetically mediated. A set of psychological features was not sufficient evidence to posit a temperamental disposition. Chronic shyness with strangers, for example, need not be due to a temperamental bias, because some shy adults could have acquired that trait during adolescence. A combination of a psychological profile and its presumed biological foundation represents the ideal definition of a temperament. Combining behavior with biological measures is common in other domains. An individual born with the genes for compromised pancreatic function who has normal blood sugar levels is not diabetic. An adolescent born to two schizophrenic parents who displays one non debilitating marker of this illness is not regarded as schizophrenic as long as he or she does not display any of the primary symptoms that define the category. However, the lack of insight into the biological contribution to temperament has meant that, at present, the psychological features compose the primary definition of temperament. The definition of temperament offered here suggests the potential error in classifying a trait as temperamental simply because it is stable over long periods of time. Future research on the temperaments will gather biological data and, if possible, begin with observations of young children. As investigators discover sensitive biological markers for each of the temperamental types, they will be able to separate groups of children or adults who display similar behavioral phenotypes into those who probably do and probably do not possess the relevant temperaments. The research of Davidson (1994, 1995) and Fox, Schmidt, Calkins, Rubin, & Coplan (1996) on asymmetry of alpha power in frontal areas illustrates this point. These investigators suggest that greater activation in the right frontal area than in the left (that is, greater desynchronization of alpha frequencies on the right side) is a sensitive sign of a temperamental vulnerability to uncertainty and/or anxiety. As a result, scientists can gather the electroencephalograph (EEG) data on groups of anxious adults and parse these samples into distinct groups based on the presence or absence of right-hemisphere activation. This suggestion is not fanciful. My laboratory has been following a large group of middleclass, Caucasian children who were evaluated initially at 4 months of age (see Kagan, 1994). Twenty percent of the infants, called high reactive, displayed high levels of motor activity and distress to a variety of unfamiliar stimuli; 40% of the sample, classified as low reactive, showed the complementary profile of minimal motor activity and distress. More children from the high-reactive group became shy and fearful in the second year, whereas most low reactives became relatively sociable and fearless.