During goal directed activity (away from oneself), some brain regions show decreased activity. Activity in these areas spring back while at rest or engage in self referential tasks. This brain network is the default mode network and includes superior and inferior anterior medial frontal regions, lower precuneus, and posterior lateral parietal cortices. This network plays a crucial role in self-referential processing.
Self referential tasks (tasks that involve perspective taking of intentions, beliefs and desires of others, remembering own past,planning own future ) are altered in schizophrenia and depression. Self- outside boundaries are blurred in schizophrenia ie fails to differentiate exogenous from endogenous stimuli. self referential (self generated) memory is poor in schizophrenia but external source memory is intact. Medial frontal cortex is the key to self referential processing. As self referential processing is poor, hypoactivity in medial frontal cortex is expected in schizophrenia. Self focus is increased in major depression ie negative ideas are extensively attributed to self and this manifest in rumination. As self referential processing is increased, the resting state is likely to be hyperactive in depression.
Contrasting resting state function is expected in these two disorders. Is this supported by evidence?
Simone Kuhn and Jurgen Gallinat report the results of a meta analysis of all f MRI /PET studies on resting state alterations in medial frontal cortex that compared patients with healthy controls. Meta-analysis include 11 studies reporting 140 foci of altogether 567 participants for schizophrenia and 11, studies with 70 foci of altogether 470 participants for depression.
There is a decrease in resting-state (hypoactivity) compared with healthy controls in ventromedial prefrontal cortex (vmPFC) in schizophrenia. In contrast, hyperactivity was seen in major depression.
Resting state activity is reduced in schizophrenia. This could explain the reduction in self referential processing and lack of insight. In contrast to this, resting activity is increased in depression and this goes with the idea of increased rumination and self focus in depression.
Summary of the article:
Kühn S, Gallinat J.Schizophr Bull. 2013 Mar;39(2):358-65