Biological Correlates of an Internet-based Psychological Intervention for Depression

Dysregulation of the hypothalamus-pituitary-adrenal (HPA) axis as well as maladaptive activation of the autonomic nervous system (ANS) are discussed as relevant factors in the development of a major depressive episode and as a correlate of its clinical manifestation. Preliminary evidence suggests that the hypercortisolaemic pattern in a subgroup of depressed patients may predict non-responses to psychotherapeutic treatment. At the same time, it is conceivable that disorder-related alterations in HPA axis and ANS regulation change in response to effective treatment, such as cognitive behavioural therapy (CBT), and that those changes could parallel changes in depressive symptoms. Identifying such associations may shed light on biological and psychological mechanisms of action underlying successful treatment.

However, so far, no studies have investigated depressed patients with regard to dysregulation in both stress systems, HPA axis and ANS, before psychotherapeutic treatment, nor have changes in functioning of both systems been inspected in response to treatment. Moreover, a detailed investigation of depressive symptom trajectories over the course of treatment and its associations with changes in HPA axis and ANS regulation is lacking. It can be speculated that specific techniques of the treatment, e.g., typical CBT elements, such as behavioural activation or cognitive restructuring, might particularly be associated with changes in HPA axis and ANS regulation.

The main aims of this project are to investigate:

1. whether diurnal salivary cortisol and alpha-amylase as well as hair cortisol concentrations change from pre- to post-intervention in treatment responders compared to non-responders;
2. whether diurnal salivary cortisol and alpha-amylase concentrations change from pre- to mid-intervention and from mid- to post-intervention in treatment responders compared to non-responders;
3. whether changes in diurnal salivary cortisol, alpha-amylase and hair cortisol concentrations are significantly correlated with changes in depressive symptoms;
4. whether concentrations of diurnal salivary cortisol and alpha-amylase as well as hair cortisol at pre-treatment predict future treatment response (i.e., on a psychological level).

On an exploratory level, it will be investigated: 5. which elements of a CBT intervention for depression (behavioural activation vs. cognitive restructuring) are associated with changes in diurnal salivary cortisol and alpha-amylase concentrations.

It is hypothesised:

1. that pre- to post-intervention decreases in diurnal salivary cortisol and alpha-amylase as well as hair cortisol concentrations will be more pronounced in responders compared to non-responders.
2. that pre- to mid-intervention and mid- to post-intervention decreases in diurnal salivary cortisol and alpha-amylase will be more pronounced in responders compared to non-responders.
3. that changes in depressive symptoms will significantly correlate with changes in diurnal cortisol and diurnal alpha-amylase as well as hair cortisol concentrations.
4. that pre-intervention diurnal salivary cortisol and alpha-amylase as well as hair cortisol concentrations will be higher in future non-responders, compared to responders.