Despite considerable progress in the understanding of depression, the treatment of those who have entered a chronic course of the disorder still represents a major challenge. In order to develop more effective interventions it is important to learn more about maintaining mechanisms and the ways in which these can be addressed. Recent research has outlined aberrations in neurophysiological parameters that may serve as risk factors underlying tendencies to engage in maladaptive responses to negative mood, and that may be particularly pronounced in patients with chronic depression. Initial evidence suggests that such deficits may not be easily amenable through established treatments. The current study investigated whether mental training using mindfulness mediation, as compared to an active control training, could alter these parameters in chronically depressed patients.

Persistent engagement in maladaptive patterns of thinking is a hallmark of depression. In those who suffer from a chronic course of the disorders, tendencies towards engagement in such patterns of thinking are likely to have become habitual and automatic in nature. Recent research has begun to elucidate potential cognitive and neurophysiological bases of such persistence. There is evidence that depressed patients show significant deficits in performance monitoring (Weinberg, Dieterich, & Riesel, 2015). Research on error-related negativity (ERN), a signal that occurs briefly after commission of an error, has reported significant aberrations in depressed suggesting deficits at the early stages of processing discrepancies. Deficits in ERN have been suggested to serve as an endophenotype for depression and psychopathology more generally (Manoach & Agam, 2013). Preliminary findings suggest that deficits remain even when symptoms are reduced following established treatments. Similarly, there is evidence for increased tendencies to elaborate negative information as evidenced by stronger late positive potentials (LPP; Auerbach, Stanton, Proudfit, & Pizzagalli, 2015) and an increased rigidity of spontaneous activity of the brain during rest as indicated by increased long-range temporal correlations of spontaneous brain oscillations (LRTC; Bornas et al., 2013).

Interventions using mental training may be particularly suited to address these aberrations. Indeed even brief training in mindfulness has been found to have significant neuroplastic effects (Tang et al., 2010) The aim of the current study was therefore to investigate the effects of a brief intervention using training in mindfulness meditation on the above listed parameters. Chronically depressed patients were randomly allocated to receive either a two-week mindfulness training or a resting control training. EEG was measured before and after the intervention along with self-reports of current symptoms and resilience/vulnerability factors. We expected the mindfulness training to have significantly stronger effects on ERN, LPP, and LRTC than the resting control training.

Inclusion Criteria:

• a current diagnosis of Major Depression as assessed by Structured Clinical Interview for DSM IV (First, Spitzer, Gibbon, & Williams, 2002)
• a lifetime history of depression with onset before age 19 and either chronic persistence of symptoms or a history of at least three previous episodes of depression, two of which needed to have occurred during the last two years
• self-reported severity of current symptoms on a clinical level as indicated by Beck Depression Inventory-II (Beck, Steer, & Brown, 1996) scores above 19
• age 25 to 60 thus excluding cases of late-onset depression, and e) fluency in spoken and written German.

Exclusion Criteria:

• history of psychosis or mania, current eating disorder, OCD, current self-harm, current substance abuse or dependence
• history of traumatic brain injury
• current treatment with CBT
• We allowed patients who were currently taking antidepressants into the study provided that the medication had not been changed during the last four weeks before entry into the study.