Pavlov's nervous system property of equilibrium or balance between excitatory and inhibitory processes provided the basis for Eysenck's (1957) early attempt to find a biological basis for the personality dimension of extraversion-introversion.
　 Gray (1964) reinterpreted the Pavlovian concept of strength of the nervous system within the framework of the influential Western concept of arousal; Eysenck used differences in tonic-arousal as the central concept in his later explanation of extraversion-introversion.
　Strelau (1983) translated the strength of the nervous system model in to one for human personality. His "reactivity" dimension combines the characteristics of sensitivity and endurance in reaction to the range of stimulus intensity. Strelau's "reactivity" construct is a psychological (behavioral) one and deals primarily with nonemotional reaction phenomena and only secondarily with emotional response.
　The aim of the first sensation seeking scale (Zuckerman, Kolin, Price and Zoob, 1964) was to measure a personality trait directly representing the seeking of stimulation that is highly arousing. The scale was developed to predict individual reactions to the experimental situation of sensory deprivation. Sensation seeking has to do with positive emotions like joy as well as the positive feelings produced by novel experiance.