Personality and individual differences in spinal motoneuronal excitability.

Abstract

ABSTRACTAlthough individual differences in sensation‐seeking are characterized by a wide range of differences in the expression of motor behavior, the psychophysiological correlates of these characteristics have not been extensively explored. In the present investigation the response characteristics of compound muscle action potentials, the H‐reflex and associated motor responses, were examined in young adult subjects who were administered the Sensation Seeking Scale (Zuckerman, 1979) and the Eysenck Personality Questionnaire (Eysenck & Eysenck, 1975). Variations in reflex responses were observed using two independent procedures. A paired stimulus method assessed the extent of reflex amplitude recovery at varying pulse intervals. A second method, termed homosynaptic depression, examined motoneuronal excitability in response to trains of pulses delivered at varying rates. The personality groups did not differ with respect to the intensity of stimulation required to elicit muscle action potentials or the nerve conduction velocities of those potentials. High disinhibition and high extraversion groups displayed reduced motoneuronal excitability as assessed by analysis of reflex recovery functions. For extraversion, similar effects were observed with the homosynaptic depression measure. These results demonstrate that individual differences in disinhibition and extraversion can be referred to discrete levels of CNS motor system activity. In this context, stimulus seeking behavior is not distinguished by a need for stimulation (initial hypoexcitability) but reflects instead reduced motor excitability which becomes evident once motoneuronal activity is initiated.