The Mental Simulation of Motor Incapacity in Depression

Running head: MENTAL SIMULATION IN DEPRESSION

The Mental Simulation of Motor Incapacity in Depression

Lisa M. Lindeman and Lyn Y. Abramson

University of Wisconsin, Madison

Abstract

In depression, negative beliefs are coupled with profound physical weakness. Specifically, the belief that one is incapable of altering events in order to prevent expected negative outcomes or bring about positive outcomes leads to bodily symptoms characterized by low energy, slow motor movement and delays in the initiation of movement. The purpose of this paper is to present a theoretical model describing the causal mechanisms that link these cognitive and somatic elements of depression. We propose that 1) the inability to alter events is conceptualized metaphorically as motor incapacity, 2) as part of this conceptualization, the experience of motor incapacity is mentally simulated, and 3) this simulation leads to both subjective feelings of lethargy and peripheral physiological changes consistent with motor incapacity.

The Mental Simulation of Motor Incapacity in Depression

According to cognitive theories of depression, depression is prompted by negative cognitive evaluations of life events (Abramson et al., 1989, 2002; Beck, 1967, 1987; Clark, Beck, & Alford, 1999). These negative evaluations involve "the expectation that highly desired outcomes will not occur or that highly aversive outcomes will occur and that one cannot change this situation" (Abramson et al., 2002, p. 269) Specifically, depression arises when a negative life event of personal importance is evaluated as stable (likely to persist over time) and global (likely to affect many other areas of life), expected to lead to other negative consequences, and taken as evidence that one is unworthy or deficient. Thus, a proximal, sufficient cause of depression is hopelessness, where, in the face of negative events believed to be pervasive and enduring, people believe that they are powerless.

Hopelessness leads to a cluster of bodily symptoms that include low energy, retarded initiation of voluntary responses, and psychomotor retardation (Abramson et al., 1989; Joiner et al., 2001). Psychomotor retardation is characterized by immobility or slowed motor movement, delays in motor activity, postural slumping, attenuated facial expression, and slowed speech (Parker & Brotchie, 1992; Widlцcher, 1983). Psychomotor retardation is positively correlated with the degree and onset of depression (Nelson & Charney, 1981; Parker, 1990; Rush et al., 1994; Parker et al., 1994) and Global Assessment of Function (GAF) but not psychotic symptoms (Hickie, Mason, & Parker, 1996). Psychomotor retardation also clusters together with sadness on the Hamilton Depression Rating Scale (items 1 and 8) in people with major depression, according to a factor analysis (Cleary & Guy, 1975). Psychomotor retardation severity is correlated with the success of therapeutic interventions (Widlцcher & Daniel, 1983), predicts fluoxetine nonresponse (Taylor, 2004), and mediates the negative effects of maternal depression on emotional development in children (Beeber & Leeman, 2002).

How does hopelessness, or the belief that one is incapable of avoiding negative events or reaching a goal, lead to slowed motor movements and lethargy? Although cognitive theories of depression (e.g., Abramson, 2002; Beck, 1987) assert that deficits in response initiation follow naturally from expectations of powerlessness and hopelessness, we suggest that explanations for this link should and can be elaborated. It seems intuitive that the promise of failure should dampen efforts to succeed. However, why should hopelessness with respect to an abstract goal, like building a positive reputation, lead to impaired response initiation with respect to concrete motor goals, like reaching for a cup of tea? In other words, why should a perceived inability to alter abstract aspects of life foster an inability to alter one's physical surroundings? Recent research on embodied cognition, conceptual metaphor, and mental imagery offers some clues. Mental concepts appear to involve the mental simulation of sensory perceptions and motor actions. For concepts regarding intangibles, such as honor, obligation, or freedom, these sensorimotor simulations are often metaphorical (Gallese & Lakoff, 2005). For example, on this basis, the concept of freedom from political oppression involves simulating the ability to freely move one's body. These simulations are the bodily experiences that were initially associated with the concept in early development. Finally, research on mental imagery demonstrates that sensorimotor simulations produce corresponding physiological effects, as if one were reliving the experience (see Cuthbert, Vrana, & Bradley, 1991, for a review).

The purpose of this paper is to propose a theoretical model describing the causal pathways linking certain cognitive and somatic elements of depression. We hypothesize that 1) hopelessness and powerlessness are conceptualized metaphorically as motor incapacity (Lakoff & Johnson, 1980, 1999), 2) the sensorimotor experience of motor incapacity is mentally simulated or reenacted, and 3) this simulation produces corresponding peripheral physiological effects. We conclude that the metaphorical mental simulation of motor incapacity is largely responsible for the low energy and psychomotor retardation seen in depression. Of note, these symptoms do not characterize all forms of major depression, and other processes may give rise to psychomotor retardation. This model specifically addresses the causal mechanisms that link hopelessness to low energy and psychomotor retardation for cases in which both of these symptoms do arise.

Background

The proposed model is rooted in three areas of research: embodied cognition, conceptual metaphor, and mental imagery. This section briefly reviews evidence supporting the general notions that concepts produce mental simulations of sensory-motor experience, and these simulations should have peripheral physiological effects.

The Nature of Concepts

In the embodiment paradigm, concepts, rather than consisting of arbitrary symbols for things in the world, involve mental simulations of perceptions and actions using many of the same neurons as actual perception and action (Barsalou, 1999; Gallese & Lakoff, 2005; Lakoff & Johnson, 1980, 1999).