Catecholamines, including epinephrine (E), norepinephrine (NE), and dopamine (DA), are associated with the response to stressful conditions. However, the relationships of catecholamines with intelligence and their interactions with stress remain unclear. This study assessed stress, intelligence quotient (IQ), and catecholamine levels in 70 healthy subjects to elucidate associations between catecholamines and stress, and between catecholamines and IQ. Additionally, the associations of catecholamines with stress and IQ were analyzed according to hemispheric dominance using the Brain Preference Indicator (BPI). There were positive correlations between the NE/E ratio and the somatization of stress but negative correlations between the E/NE ratio and the somatization of stress among the total number of subjects. In the right-brain-dominant group, a high E/DA ratio was correlated with low levels of stress, somatization and depression, and high NE/E and DA/E ratios were associated with high levels of somatization. In the left-brain-dominant group, high E levels were correlated with low levels of depression. In the total subjects, there were positive correlations between the NE/E and DA/E ratios and the sum of the vocabulary, arithmetic, picture arrangement, and block design IQ subtests. Thus, these catecholamines were associated with stress and IQ, which suggests that the autonomic functional regulation of catecholamine levels in relation to stress may also affect cognitive functions related to intelligence in the brain. Furthermore, the relationships between catecholamines and stress or IQ differed depending on hemispheric dominance, which suggests that the present results could be used to inform the development of personalized therapies based on hemispheric asymmetry.
Keywords: Dopamine; Epinephrine; Intelligence; Norepinephrine; Stress.