The Complex Role of Mental Time Travel in Depressive and Anxiety Disorders: An Ensemble Perspective
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Introduction
Depressive and anxiety disorders are two major categories of psychopathology, yet they have proven difficult to differentiate in some respects. As will be documented below, both are characterized by dysfunctional executive attention and pessimistic attributional styles, with a high degree of comorbidity. Here we build on the premise of Roepke and Seligman (2016) that the core problem in depression is a difficulty in mental time travel, specifically, an inability to envision positive events in the future. We consider the role of mental time travel in differentiating the two disorders and conclude that this component of human cognition is by itself insufficient. Mental time travel, we suggest, is moderated by problems with executive attention and an interpretive component responsible for causal attributions and inner speech.In an important paper, Roepke and Seligman (2016) argued that prospection, or the mental representation of future events, plays a major role in depression. Human episodic memory enables mental time travel, that is to say, the ability both to recall past autobiographical events and to imagine possible future events (Tulving, 2002). Roepke and Seligman suggested that the negative beliefs about the future and feelings of hopelessness that characterize depressive disorders (Beck, 1974) can be directly linked to faulty prospection, an inability to envision possible futures and poor evaluation of possible futures. In their view, “.faulty prospection is the core causal process of much depression” (p. 24). A similar proposal was advanced by Miloyan et al. (2014) to account for depression; they also extended the analysis by suggesting that a different form of faulty prospection, centered on worry rather than pessimism and hopelessness, lay at the core of anxiety disorders.
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We agree that problems with mental time travel are central to psychopathology, but we question whether this component can be isolated from other cognitive components to ascertain its relative contribution. Instead, we argue that other fundamental components of human cognition are concurrently at work in both depressive and anxiety disorders. In our view, it is important to consider how other components impair or even enhance the functioning of mental time travel. To develop this perspective, we draw on the ensemble hypothesis, which holds that human cognition depends on five core systems or components that interact in non-additive ways (Kellogg, 2013; Kellogg and Evans, 2019). Mental time travel is necessary but not sufficient for explaining either the remarkable competencies of human cognition or its breakdowns in disorders such as anxiety and depression. An advanced executive form of working memory, a theory of mind augmenting social cognition, language, the ability to interpret information using inner speech, and causal inference are necessary, as well as an episodic memory capable of mental time travel. Kellogg (2013) introduced the ensemble hypothesis in the context of understanding the exceptional cognitive abilities in the evolution of our species, Homo sapiens. The book provides the reasons for considering the five components and their interactions in normally developing and functioning human beings. Kellogg and Evans (2019) offered further evidence in support of the hypothesis from behavioral studies, lesion studies, and studies involving neuro-atypical populations.
The key claim of the ensemble hypothesis is that two or more mental capacities can interact in a multiplicative fashion to yield competencies in a well-functioning human being that exceed their simple additive effects. For example, delay of gratification is a phenomenon that entails an ability both to prospectively consider the future and to exercise cognitive control using executive attention. In typically developing children, growth in the capacity of executive attention for self-regulation boosts the ability to delay rewards in anticipation of a larger future reward (Mischel et al., 1989). Similarly, planning in problem solving requires future thinking and a normally functioning system of executive attention. Frontal lobe injuries that damage networks of executive attention often impair planning (Kellogg and Evans, 2019). In normally functioning adults, retrospective memory for a list of words presented in a laboratory task requires an intact hippocampus and medial temporal lobe, but it is also boosted by maintenance and elaborative rehearsal strategies that depend on executive attention. Failing to deploy attentional resources to an encoding strategy impairs the recall of a list of words presented in a laboratory task in individuals with depression (Hertel and Rude, 1991). As will be considered in detail later, the normal functioning of mental time travel can be altered by depression because of its effects, in part, on executive attention.
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The key claim of the ensemble hypothesis is that two or more mental capacities can interact in a multiplicative fashion to yield competencies in a well-functioning human being that exceed their simple additive effects. For example, delay of gratification is a phenomenon that entails an ability both to prospectively consider the future and to exercise cognitive control using executive attention. In typically developing children, growth in the capacity of executive attention for self-regulation boosts the ability to delay rewards in anticipation of a larger future reward (Mischel et al., 1989). Similarly, planning in problem solving requires future thinking and a normally functioning system of executive attention. Frontal lobe injuries that damage networks of executive attention often impair planning (Kellogg and Evans, 2019). In normally functioning adults, retrospective memory for a list of words presented in a laboratory task requires an intact hippocampus and medial temporal lobe, but it is also boosted by maintenance and elaborative rehearsal strategies that depend on executive attention. Failing to deploy attentional resources to an encoding strategy impairs the recall of a list of words presented in a laboratory task in individuals with depression (Hertel and Rude, 1991). As will be considered in detail later, the normal functioning of mental time travel can be altered by depression because of its effects, in part, on executive attention.
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The purpose of the present paper is to consider the implications of the ensemble hypothesis for two broad categories of psychopathology: depression and anxiety. We suggest that much of the phenomenology and symptoms that underlie depressive and anxiety disorders can best be understood as an interaction of components of the hypothesized ensemble. We wish to extend the insights provided by Miloyan et al. (2014) and Roepke and Seligman (2016) by demonstrating how the interpreter and executive attention influence mental time travel. As will be seen, language is considered in the form of inner speech, but the broader concept of language as interpersonal communication falls outside the scope of the current paper. Similarly, as will be addressed in the limitation section of our paper, an extensive literature on theory of mind and social cognition in depression ultimately needs to be accounted for. Even so, our focus on the interpreter, executive attention, and mental time travel documents the importance of the interactions posited by the ensemble hypothesis.
To illustrate, consider the case of depression (see Figure 1), as exemplified by major depressive disorder (MDD). As will be discussed in detail later, the interpreter shown in Figure 1 refers to the inner voice and causal inference capacity of the left hemisphere of the human brain that enables attributions about the self and other people (Gazzaniga, 2000; Kellogg, 2013). In depression, the interpreter is biased to assign blame to the self for negative experiences. This pessimistic and personally negative explanatory style (Petersen and Seligman, 1984) causes the depressed individual to focus attention on negative past events and have difficulty envisioning anything positive about the future. Further, there is evidence that depression is associated with a concurrent deficit in executive attention (Ólafsson et al., 2011), causing impaired cognitive control over mental time travel resulting in persistent negative rumination. Thus, the influence of both a bias in interpretation and a deficit in executive attention, we propose, could underlie faulty prospection in depressed individuals. The interactive model of Figure 1 differs from the position of Roepke and Seligman (2016) with respect to effective approaches to treatment for depression. They advocate for treatments targeting mental time travel, specifically, the core problem with prospection. Alternately, we contend that efforts to improve executive attention and to correct the pessimistic explanatory style of the interpreter ought not be neglected, because they can alter the functioning of mental time travel.
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To illustrate, consider the case of depression (see Figure 1), as exemplified by major depressive disorder (MDD). As will be discussed in detail later, the interpreter shown in Figure 1 refers to the inner voice and causal inference capacity of the left hemisphere of the human brain that enables attributions about the self and other people (Gazzaniga, 2000; Kellogg, 2013). In depression, the interpreter is biased to assign blame to the self for negative experiences. This pessimistic and personally negative explanatory style (Petersen and Seligman, 1984) causes the depressed individual to focus attention on negative past events and have difficulty envisioning anything positive about the future. Further, there is evidence that depression is associated with a concurrent deficit in executive attention (Ólafsson et al., 2011), causing impaired cognitive control over mental time travel resulting in persistent negative rumination. Thus, the influence of both a bias in interpretation and a deficit in executive attention, we propose, could underlie faulty prospection in depressed individuals. The interactive model of Figure 1 differs from the position of Roepke and Seligman (2016) with respect to effective approaches to treatment for depression. They advocate for treatments targeting mental time travel, specifically, the core problem with prospection. Alternately, we contend that efforts to improve executive attention and to correct the pessimistic explanatory style of the interpreter ought not be neglected, because they can alter the functioning of mental time travel.
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The plan of the paper is, first, to introduce several components of the ensemble hypothesis that are central to our analysis of depressive and anxiety disorders. Second, we consider evidence on the role of mental time travel in depressive and anxiety disorders. Third, we discuss literature regarding the pessimistic explanatory style in depression and suggest that anxious individuals are characterized by a related but distinct dysfunctional style of explaining events as threatening to the self. The emphasis on loss in depression and threats in anxiety can influence the functioning of mental time travel, we propose. Fourth, we document that both kinds of disorders are associated with impairments in executive attention that may compound problems with mental time travel. Fifth, we discuss how the symptoms of depression versus anxiety can best be understood by considering mental time travel, the interpreter, and executive attention as an integrated ensemble. We conclude by considering the implications of the ensemble perspective regarding effective therapies for depressive and anxiety disorders.
Mental Time Travel, the Interpreter, and Executive Attention
Mental time travel is the unusual form of human episodic memory that allows the mind to recollect the specific time and place of a past event in one’s personal history (Tulving, 2002; Suddendorf and Corballis, 2007). It is conceived as mental time travel because the same neural systems are involved in imagining future events as well as recollecting past events. The brain systems involved in mental time travel include the hippocampus and medial temporal lobe structures as well as the default mode network activated in resting state conditions when no external task is presented (Buckner et al., 2008). The ability to construct spatially coherent scenes in which an event takes place is essential in both recollecting the past and imagining the future. It has been suggested that scene construction is a core function of the hippocampus (Clark and Maguire, 2016).Click here to buy the Mental time travel system
A uniquely human mental ability appears to be the interpretive capacity of the left hemisphere (Gazzaniga, 2000). Over the course of human evolution, our oral language capacity became internalized as inner speech, mediated by language networks in the left hemisphere. Vygotsky (1962) emphasized that speech begins in early childhood as a means for communication, but as speech is internalized, it also becomes a means for planning and problem solving. Self-directed inner speech, then, has long been recognized as an important vehicle for thinking and appraising situations and events. The interpreter constructs a personal narrative that explains why we feel and behave as we do. Inner speech is combined with a specialization of the left hemisphere for a specific kind of thinking. The left hemisphere is not only specialized for the use of language, including self-directed language of inner speech, but it is also specialized for forming hypotheses (Wolford et al., 2000) and making inferences about causal relationships (Roser et al., 2005). Similarly, the ability to reason deductively is known to be impaired in patients with left frontal lesions but not right frontal lesions (Reverberi et al., 2010).
In clinical psychology, the interpreter is important in understanding the role of inner speech and causal inference in how people respond to stressful life events. How an individual cognitively appraises stressors can either attenuate or exacerbate the strain that they cause. This role for causal attributions has long been recognized in understanding depressive and anxiety disorders. For example, Petersen and Seligman (1984) highlighted that depression is characterized by a personalized and pessimistic explanatory style. The individual attributes personal, pervasive, and permanent causes to negative personal experiences, committing what social psychologists call the fundamental attribution error. The role played by the interpreter in explaining why things happen and what significance events have for the self is central to both depression and anxiety, as will be detailed later in the paper.
The executive attention component of working memory enables the coordination and regulation of representations held in verbal, visual, and spatial stores of short-term memory. Working memory, planning, cognitive control, self-regulation, and response inhibition have all been referred to as executive functions that have traditionally been viewed as dependent on the frontal lobe (Alvarez and Emory, 2006; Posner and Rothbart, 2007; Diamond, 2013; Ajilchi and Nejati, 2017). A more complex understanding has emerged in the literature with two distinct brain networks involved in executive attention; these include but are not limited to regions in the frontal lobe (Posner and Peterson, 1990; Petersen and Posner, 2012).
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In clinical psychology, the interpreter is important in understanding the role of inner speech and causal inference in how people respond to stressful life events. How an individual cognitively appraises stressors can either attenuate or exacerbate the strain that they cause. This role for causal attributions has long been recognized in understanding depressive and anxiety disorders. For example, Petersen and Seligman (1984) highlighted that depression is characterized by a personalized and pessimistic explanatory style. The individual attributes personal, pervasive, and permanent causes to negative personal experiences, committing what social psychologists call the fundamental attribution error. The role played by the interpreter in explaining why things happen and what significance events have for the self is central to both depression and anxiety, as will be detailed later in the paper.
The executive attention component of working memory enables the coordination and regulation of representations held in verbal, visual, and spatial stores of short-term memory. Working memory, planning, cognitive control, self-regulation, and response inhibition have all been referred to as executive functions that have traditionally been viewed as dependent on the frontal lobe (Alvarez and Emory, 2006; Posner and Rothbart, 2007; Diamond, 2013; Ajilchi and Nejati, 2017). A more complex understanding has emerged in the literature with two distinct brain networks involved in executive attention; these include but are not limited to regions in the frontal lobe (Posner and Peterson, 1990; Petersen and Posner, 2012).
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By studying a battery of executive functioning tasks, Miyake et al. (2000) identified three correlated but distinctive processes underlying performance. Updating the contents of working memory, shifting goals as required in multitasking, and inhibiting irrelevant information are considered three essential and irreducible functions of executive attention. A widely used test of individual differences in working memory capacity, called the Operation Span (OSPAN) test, indicates that the ability to inhibit irrelevant information is especially important and shows a strong correlation with general fluid intelligence or the ability to solve novel problems (Engle et al., 1999).
Mental time travel, the interpreter, and executive attention are three fundamental components of human cognition. Kellogg (2013) proposed that these components, together with theory of mind and language, comprise an ensemble that renders human cognition unique and qualitatively different from non-human cognition. Importantly, his hypothesis suggests that it is the interaction of these components that yields the unique properties of human cognition. If that is so, then it stands to reason that common forms of psychopathology should reveal such interactions, too. In persons experiencing anxiety or depression, a deficit in one component can cascade to degrade the functioning of another component, despite that the latter component is not necessarily dysfunctional.
Mental time travel, the interpreter, and executive attention are three fundamental components of human cognition. Kellogg (2013) proposed that these components, together with theory of mind and language, comprise an ensemble that renders human cognition unique and qualitatively different from non-human cognition. Importantly, his hypothesis suggests that it is the interaction of these components that yields the unique properties of human cognition. If that is so, then it stands to reason that common forms of psychopathology should reveal such interactions, too. In persons experiencing anxiety or depression, a deficit in one component can cascade to degrade the functioning of another component, despite that the latter component is not necessarily dysfunctional.
Mental Time Travel Impairments
Click here to buy the Mental time travel systemRoepke and Seligman (2016) reviewed a variety of evidence that faulty prospection lies at the heart of depression. First, persons experiencing depression can envision negative future scenarios more readily, compared to non-depressed persons (MacLeod and Byrne, 1996). This characteristic is also shared with those experiencing anxiety, indicating it is not a unique dysfunction of mental time travel associated with depression. Miloyan et al. (2014) suggested that anxious as well as depressed individuals anticipate negative future events but that each disorder shows a unique profile of faulty prospection. Individuals with anxiety anticipate more negative experiences, but not fewer positive experiences, relative to control participants without a history of psychiatric diagnosis, according to some studies (MacLeod and Byrne, 1996; MacLeod et al., 1997b). Depression, on the other hand, is associated with a failure to anticipate positive future events (Miranda and Mennin, 2006; Pomerantz and Rose, 2014). When depressed psychiatric outpatients were asked to describe a distressing personal problem and to imagine and rate the likelihood of both the worst and best possible outcomes, they rated the worst outcome as being more likely and the best outcome as being less likely, relative to generalized anxiety disorder (GAD) and control groups (Beck et al., 2006).
Thus, it is possible that a faulty form of prospection found in depression results in a diminished ability to envision positive future events (MacLeod and Salaminiou, 2001). However, both this finding and the finding that individuals with depression envision more negative future events than do controls can also be linked to a pessimistic explanatory style. MacLeod et al. (1997a) found that both depressed and anxious patients not only judged future negative events to be more likely, relative to controls; they also provided more supportive as opposed to contradictory reasons for their occurrence. As MacLeod et al. (p. 22) concluded, “…mood-disturbed subjects were pessimistic about what would happen to them in the future, and this was supported by their causal thinking about those events.” Thus, the pessimistic explanatory style of the interpreter rather than a malfunction in mental time travel per se could explain the findings. They could also be linked to the deficits in executive attention that are associated with depression (Ólafsson et al., 2011). As will be argued in later sections of the paper, problems with mental time travel may arise because of the moderating influences of the interpreter and executive attention.
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Thus, it is possible that a faulty form of prospection found in depression results in a diminished ability to envision positive future events (MacLeod and Salaminiou, 2001). However, both this finding and the finding that individuals with depression envision more negative future events than do controls can also be linked to a pessimistic explanatory style. MacLeod et al. (1997a) found that both depressed and anxious patients not only judged future negative events to be more likely, relative to controls; they also provided more supportive as opposed to contradictory reasons for their occurrence. As MacLeod et al. (p. 22) concluded, “…mood-disturbed subjects were pessimistic about what would happen to them in the future, and this was supported by their causal thinking about those events.” Thus, the pessimistic explanatory style of the interpreter rather than a malfunction in mental time travel per se could explain the findings. They could also be linked to the deficits in executive attention that are associated with depression (Ólafsson et al., 2011). As will be argued in later sections of the paper, problems with mental time travel may arise because of the moderating influences of the interpreter and executive attention.
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An important exception regarding memory impairment in depression is the tendency to focus and elaborate upon sad events (Williams et al., 1997). A case can be made for mood congruent memory in depression (Mineka and Nugent, 1995). For example, in a study by Derry and Kuiper (1981), a list of depression-related adjectives (e.g., bleak, dismal, helpless) and non-depression-related adjectives (e.g., amiable, curious, loyal) were presented in an incidental learning task. The nature of the orienting task was manipulated, with one way being whether the adjective applied to the self. On a subsequent recall test, this self-reference orienting task resulted in a greater proportion of depressed-content words recalled (41%) than non-depressed content (16%) for depressed patients. Strikingly, this pattern was completely reversed for normal controls, who recalled more non-depressed content (43%) compared with depressed content (8%). Even a group of psychiatric controls showed a reversal with more non-depressed content (36%) relative to depressed content (18%). None of these effects were observed for structural (small letters?) and semantic (means the same?) orienting tasks, indicating that they are contingent on judging the word as relevant to the self.
Similarly, in another study, after being shown a list of words including pleasant, unpleasant, and neutral words, individuals with depression recalled more unpleasant words compared with pleasant words (McDowall, 1984). A non-depressed control group as well as another control group made up of psychiatric patients with a diagnosis other than depression did not show this bias toward improved memory for unpleasant words. The depressed patients’ free recall of unpleasant words was at the same level as that for the two control groups, whereas they showed a memory impairment for pleasant words. This indicates that the mood congruent benefit of remembering unpleasant words can offset the usual memory impairment found in depression.
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Similarly, in another study, after being shown a list of words including pleasant, unpleasant, and neutral words, individuals with depression recalled more unpleasant words compared with pleasant words (McDowall, 1984). A non-depressed control group as well as another control group made up of psychiatric patients with a diagnosis other than depression did not show this bias toward improved memory for unpleasant words. The depressed patients’ free recall of unpleasant words was at the same level as that for the two control groups, whereas they showed a memory impairment for pleasant words. This indicates that the mood congruent benefit of remembering unpleasant words can offset the usual memory impairment found in depression.
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Clark and Teasdale (1982) found that autobiographical experiences also reveal mood congruency even within the same group of individuals with depression. The investigators compared the recall of personal memories at two different times of day to capitalize on diurnal variations in mood among psychiatric patients experiencing depression. The percentage of unhappy memories (52.3%) was reliably greater when the individual reported being more depressed compared with less depressed (36.7%). Happy memories (37.7 versus 51.1%) showed exactly the reverse pattern.
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