Before you know it: cognitive changes in depression

Abstract

Depression is a common mental disorder affecting an estimated 350 million people globally (World Health Organization, 2016). Despite the global prevalence and impact of depression, the main treatments, including antidepressant drugs and psychotherapy, are only partly effective (Arroll et al., 2009; Bschor & Kilarski, 2016; Churchill et al., 2013; Churchill et al., 2010) and further research is therefore required to better understand and treat this illness. Although the symptoms of depression are heterogeneous, two specific cognitive symptoms appear to be relatively ubiquitous: (a) an impaired ability to disengage from negative material (Armstrong & Olatunji, 2012; Donaldson, Lam, & Mathews, 2007; Gotlib & Joormann, 2010; Koster, De Lissnyder, Derakshan, & De Raedt, 2011; Koster, De Raedt, Goeleven, Franck, & Crombez, 2005); and (b) a distortion in the processing of temporal intervals, leading to a sensation that time is dragging (Bschor et al., 2004; Kitamura & Kumar, 1982; A. Lewis, 1932; Sevigny, Everett, & Grondin, 2003; Wyrick & Wyrick, 1977). The specific aims of this thesis were to investigate, using psychophysical methodologies, whether the impairment in disengagement from negative material and the distortions in temporal processing occur at 'shorter durations' (less than one second). If this is the case, it might suggest that the impairments are related to changes in the underlying mechanisms associated with attention, cognition, and temporal processing, rather than, or in addition to, the typical ruminative thinking of depression that takes place over 'longer durations'. We investigated the relationship between depression symptoms and impaired disengagement from negative and positive emotional material using an emotion-induced blindness (EIB) paradigm, which tested stimulus durations of 200ms and 800ms. No evidence was found of any relationship between depressive symptoms and impaired disengagement from negative or positive emotion stimuli. We also investigated the relationship between depression symptoms and impairments and distortions in temporal processing. The study used a 2AFC paradigm to compare the duration of two images, neutral-neutral and neutral-negative. The reference duration was 200ms and the measures of impairment and distortion were PSE shift and WF. Once again, no evidence was found of any relationship between depressive symptoms and the impairments or distortions. Together, the findings suggest that depression symptoms were unrelated to an impaired temporal processing mechanism or impaired mechanisms responsible for the disengagement from emotion stimuli. Instead, the findings were more consistent with the cognitive models of depression. Specifically: (a) the impaired disengagement from negative material in depression was more likely to be related to rumination and its effects on attentional control rather than earlier cognitive processes (Donaldson et al., 2007; Koster et al., 2011), and, (b) the perception of time slowing in depressed individuals was likely to be related to the cognitive impairments in sustained attention, especially that people with depression tend to focus on the passage of time (Gallagher, 2012; Msetfi, Murphy, & Kornbrot, 2012). Show more