Autonomic Nervous System Function and Aging: Response Specificity

Age differences in autonomic nervous system response patterns were investigated to determine if there was an age-related increase in the tendency to respond to multiple stimuli with a consistent response hierarchy (individual consistency). Five stimuli were administered in a Latin Square design—mental arithmetic, cold pressor, isometric exercise, comic slide, and time estimation. A warning tone was presented before each stimulus. Physiological measures included heart rate, systolic and diastolic blood pressures, skin potential, breathing rate, and digital blood flow. To compare responses in different systems, responses were standardized according to the formula, Z = [50 + 10 (X ? M)]/σ, where Z is the standardized score, X is the difference between stimulation and warning levels, M is the average response for that system, and σ is the square root of the mean square for error from the analysis of variance computed for each response system. A matrix was generated for each subject which included his Z scores from the six response systems for the five stimuli. Intraclass correlations were then computed. Individual consistency significantly increased with increasing age (r= .33, p<.005).