Overgeneral and intrusive memories in depression: The role of rumination and resistance to proactive interference

Several studies have shown that depressed patients have difficulties to retrieve specific autobiographical memories in response to cue words (see Williams et al., 2007, for a review). Compared to controls, depressed patients tend to retrieve relatively more memories that summarize categories of events (e.g., when I go for a hike ) rather than memories that refer to a single episode (e.g., when I stood on top of mount Kilimanjaro , in response to happy). This memory phenomenon is called reduced autobiographical memory specificity (rAMS) or overgeneral memory (OGM). Other research has shown that depressed individuals may experience intrusive memories (e.g., Patel et al., 2007). These are very specific, involuntary, disturbing memories. Up to now, it is unclear how this paradoxical co-occurrence of rAMS (during voluntary memory retrieval) and very specific intrusive memories (during spontaneous, involuntary memory retrieval) in depressed patients can be understood. The starting point of the current dissertation was the exploration of the role of rumination as a potential explanation for this paradox. Rumination refers to repetitively thinking about the causes, meanings, and consequences of certain feelings or cognitions. It seems a likely candidate for explaining the paradox because several studies have indicated that rumination leads to rAMS (see Sumner, 2012, for a recent review), and other studies have shown that rumination also triggers intrusive memories (e.g., Watkins, 2004).Twelve studies were conducted. A recurrent finding across several of these studies was that rumination and intrusive memories are clearly associated. Furthermore, I consistently found that rumination and intrusive memories were associated with depressive symptoms. The first three chapters focus on these robust findings. In Chapter 1 and 2, three studies in non-clinical samples are presented. Chapter 3 contains a review paper. In this review paper, the concepts of rumination and intrusive memories are clarified, an overview of studies investigating rumination and intrusive memories is presented, and a theoretical account for how rumination may lead to intrusive memories is proposed. In contrast to the repeated observation that rumination and intrusive memories are associated, I failed to observe a reliable relationship between (trait-)rumination and rAMS in any of my studies (Chapter 4). I additionally aimed to examine the role of resistance to proactive interference in relation to rumination, overgeneral memories, and intrusive memories. Resistance to proactive interference refers to the executive ability to ignore interference of previously relevant but currently irrelevant cognitions (Friedman & Miyake, 2004). Research shows that impaired executive functioning is related to rAMS (see Sumner, 2012, for a recent review), and that weak resistance to proactive interference is associated with more intrusive memories of a laboratory stressor (e.g., Verwoerd, Wessel, de Jong, Nieuwenhuis, & Huntjens, 2011). These combined findings suggest that weak resistance to proactive interference may be another important player in the paradoxical co-occurrence of rAMS and intrusive memories. In Chapter 5, I present evidence that weak resistance to proactive interference is related to rAMS in students as well as in depressed patients. Weak resistance to proactive interference was, however, not related to rumination, intrusive memories, and depressive symptoms. Chapter 6 presents a study in pregnant women on the role of rumination, intrusive memories, rAMS, and weak resistance to proactive interference in predicting prospective levels of depressive symptoms. Results showed that rumination during pregnancy could reliably predict postpartum depressive symptoms. In addition, my findings suggested that experiencing intrusive memories might be a risk factor for developing depressive symptoms. Somewhat counter to predictions, rAMS during pregnancy was related to lower levels of postpartum depressive symptoms, which may suggest a protective role of rAMS. Resistance to proactive interference during pregnancy could not predict postpartum depressive symptoms, but may render women vulnerable for developing delivery-related intrusive memories. To test the causal hypothesis that rumination underlies both rAMS and intrusive memories, four experiments were conducted in which a ruminative versus non-ruminative thinking style were induced (Chapter 7). However, these experiments yielded mixed and inconclusive results. These seven chapters are preceded by a general introduction and followed by a general discussion. The general introduction contains a brief background with respect to the research questions and aims. In the general discussion, the associations between all key variables are discussed one by one in the light of their theoretical and clinical implications.status: publishe