Voluntary and involuntary mental time travel in dysphoria and depression - characteristics and mechanisms

Mental time travel (MTT) refers to an individual’s ability to mentally travel through subjective time, autonoetically re-experiencing past events under the form of autobiographical memories (past MTT), and pre-experiencing events as future autobiographical representations (future MTT). MTT can occur voluntarily, whereby a past/future autobiographical event is subjectively experienced as an intended occurrence, or involuntarily, wherein such an event is subjectively experienced as an unintended outcome of which the individual is aware. Studies investigating MTT’s characteristics in dysphoria and depression show that dysphoric and depressed individuals produce more overgeneral and negative MTT events when compared to control groups. However, existing research has been limited to past and voluntary MTT events, with few studies investigating involuntary MTT and future MTT in dysphoria and depression. The overarching aim of the present research was to compare the phenomenological characteristics of MTT in dysphoric individuals vs. normal mood individuals (Study 1), and in clinically depressed individuals vs. never-depressed individuals (Study 2), with the purpose of furthering existing knowledge on MTT and its relation with dysphoria and Major Depressive Disorder. This aim was addressed by conducting two studies, using a 2 x (2 x 2) mixed-factorial design, with temporality (past vs. future events) and type of retrieval (voluntary vs. involuntary events) as within-subjects independent variables, and participant group as a between-subjects variable. In Study 1, Portuguese university students were categorised into a dysphoric (n=17) or a normal mood group (n=39) depending on their score on the Beck Depression Inventory (BDI-IA) – cutoff point (≥ 10). In Study 2, clinically diagnosed depressed patients (n=32) were recruited from a Portuguese hospital and matched for age and gender with never-depressed control participants (n=32) recruited from the community. The dependent variables tested were: level of spatiotemporal specificity, self-relevance, mood and physical impact, valence, and visual perspective of the MTT events produced. A diary methodology was used in both studies, with an open-ended time period that lasted for a minimum of two weeks, for participants to record their MTT events and grade them on the above mentioned variables using Likert-type ratings. Between seven and fourteen MTT events were produced for each of the four MTT conditions (past voluntary, past involuntary, future voluntary, future involuntary). Results showed that when compared to their respective control groups, depressed, but not dysphoric participants, exhibited a clear influence of mood on several of the phenomenological characteristics of MTT. In Study 1 there were no statistically significant differences in the specificity, negative valence, and mood/physical impact of the MTT events produced by dysphoric and normal mood participants. On the contrary, in Study 2, results partially supported a lower specificity and fully supported a greater negativity and mood/physical impact of MTT events in depressed individuals compared with never-depressed participants. Both studies supported the greater self-relevance of voluntary MTT events and partially supported the hypothesised effect of type of retrieval in specificity. These were the first studies to directly compare past and future, voluntary and involuntary MTT events in dysphoric and depressed individuals, addressing existing gaps in the literature. The key limitation is the relatively small sample size of both studies, however each participant was comprehensively assessed for at least two weeks, providing a rich set of reliable data. Despite limitations, this thesis provides novel pilot findings that help understand the similarities and differences between involuntary and voluntary, past and future MTT, as well as providing new information regarding the possible role of MTT in dysphoria and depression