An integration between psychiatry, neurochemistry and differential psychology gives an evidence-based framework for the diagnosis of mental illness rooted both in modern neurophysiology and clinical observations.

To investigate whether, a neurochemical model of temperament might (FET) provide a better discrimination between major depression (MD), anxiety (GAD), co-morbid depression and anxiety and delusional disorders than existing emotionality-based temperament models.

Three studies compared the profiles on temperament and personality disorder inventories in patients who were diagnosed and treated for named disorders across four adult age groups (17–24, 25–45, 46–65, 66–84).

The FET distinguished between MD and GAD in line with the DSM descriptors and showed significant differences for the traits of motor endurance and motor tempo (much lower values in MD), and neuroticism (much higher value in GAD). The results showed benefits of differentiation between physical and social types of fatigue as a symptom of MD and that high impulsivity and low plasticity can be also considered symptoms differentiating between mental disorders. Moreover, high sociability appeared as a symptom associated with high dominance–mania tendencies. The FET framework appeared to be sensitive to age and sex differences: higher anxiety and anti-social symptoms appeared to be more prominent in the younger age (unlike depression symptoms), and declined with age.

This study suggest the utility of using a functional approach to both taxonomy of temperament and classification of mental disorders and the benefits of systemic differentiating between 12 functional aspects of behavior, with special attention to non-emotionality-related aspects of behavior.

The author has not supplied his/her declaration of competing interest.