Recall performance, plasma cortisol and plasma norepinephrine in normal human subjects

This study investigated hypothalamic-pituitary-adrenal (HPA)-axis and sympathetic nervous system (SNS) correlates of recall performance in normal human subjects. Twenty-two normal human subjects were given one memory task: short-term recall of unrelated non-organizable lists of neutral words, in immediate recall conditions. Two types of memory were individualized: measures reflecting effortful processing and measures reflecting automatic processing, which were related to 3 daytime plasma cortisol (CORT) and plasma NE values, and assessed after venipuncture. It was hypothesized that plasma CORT is positively related and plasma norepinephrine (NE) is negatively related to effortful processing. Pearson correlation was computed and regression analysis was performed. Positive correlation appeared between plasma CORT values and negative correlation appeared between plasma NE values and measures reflecting effortful processing. However, stepwise multiple regression analysis showed that only morning plasma CORT values are functionally positively and afternoon plasma NE values are functionally negatively related to effortful processing. This suggests that morning HPA-axis activities enhance and afternoon SNS activities inhibit effortful processing.