Intrinsic activity temporal structure reactivity to behavioural state change is correlated with depressive symptoms

Abstract

Patients with major depressive disorder (MDD) tend to focus their thoughts on their personal problems and negative self-reflection. This negative self-focus has a major impact on patient quality of life and is associated with a range of cognitive deficits. Self-related thoughts, such as those seen in rumination, have been associated with intrinsic activity within cortical midline structures. In normal conditions this intrinsic activity is responsive to behavioural state, changing as an individual switches from an internally to externally oriented context. It was hypothesised that this responsiveness would be blunted in patients with MDD (n = 26; control n = 37) and that the degree to which an individual was fixed in a particular intrinsic state would be correlated with reported ruminatory behaviours. This was tested by measuring intrinsic EEG activity temporal structure, quantified with detrended fluctuation analysis (DFA), in eyes-closed and eyes-open task-free states and contrasting between the conditions. The difference between the internally oriented eyes-closed and externally oriented eyes-open states was then correlated with ruminatory behaviour, measured with the Rumination Response Scale. Healthy controls showed a robust beta band DFA change between states, moving from a critical to sub-critical activity state with the opening of the eyes. This change was not seen in MDD patients, with the eyes-closed DFA remaining similar to that in eyes-open. A negative correlation was seen between the DFA difference and rumination scores over the midline electrodes. These results identify a reduced reactivity of intrinsic activity properties in MDD that is related to greater ruminative symptoms.