Psychophysiology and Eating Disorders
Patricia P. Sanchez Gomez, Nicholas A. Troop and Janet L. Treasure
For psychiatric disorders such as eating disorders in which psychological conflicts seem to be essentially played out on the body, psychophysiology is an important avenue of exploration. Apparently abnormal behaviours in relation to food and weight may be associated with an abnormal psychophysiological response to such stimuli.
One advantage of taking psychophysiological measures, is that this approach is relatively objective and may therefore overcome some of the characteristic biases of other techniques (Lattimore, Gowers and Wagner, 2000) such as the confounding in self-report measures caused by patients' motivational states (e.g. trying to make sense of the illness or even to punish/reward a therapist) and co-morbidity with mood or personality disorders. For example, several studies have shown elevated rates of alexithymia in individuals with eating disorders (Bourke et al., 1992; Schmidt, Jiwany and Treasure, 1993). Alexithymia is a personality construct denoting difficulties in identifying and expressing feelings, an impoverished imaginative life, and an externally oriented cognitive style with thoughts characterized by pragmatic contents (Taylor et al., 1996; Corcos et al., 2000). Individuals displaying these characteristics may systematically misreport their inner states. Thus an objective assessment of emotional responses to food stimuli by monitoring of indices of autonomic arousal can be informative. Among these indices heart rate, blood pressure, skin conductance, finger temperature, respiration and eye movement variability are the most widely used (Leonard et al., 1998; Parrott and Hertel, 1999).
There has been a relative lack of psychophysiological research in patients with either anorexia or bulimia nervosa. However, eating disorders can be set within a dimensional framework in which the clinical conditions merge on the continuum of eating behaviour from dietary restraint to overeating and on the continuum of body weight from emaciation to obesity. Therefore, in addition to studies using clinical groups of patients, we include in this review those studies that report on the psychophysiological responses of dieters and overeaters and in people of different weight groups.
Studies have generally used two types of provocative stimuli to elicit a physiological response. The first relates directly to the symptoms and includes food and body shapes (either real, pictorial or imagined). The second involves exposing participants to some kind of stressor such as a difficult cognitive task (such as unsolvable anagrams) or speech threat (where participants prepare a talk that they believe they will have to present to a group of judges). Below we review studies that measure psychophysiological responses to both of these kinds of stimuli. These studies are summarized in Table XXTJI–5.1.
ASSESSMENT IN EATING DISORDERS
There are some limitations in using psychophysiological methods to assess the autonomic arousal in patients with eating disorders. In the first place, basal autonomic tone may differ from that of noneating disordered women, particularly, for example, in those who are emaciated. Leptin levels are lower in those who are in a state of starvation and leptin is known to affect activity in the autonomic nervous system. Research has shown that patients with anorexia nervosa and bulimia report high levels of anxiety and depression (de Zwaan et al., 1996; Phillips, Tiggeman and Wade, 1997; Godart et al., 2000) and these variables should also be taken into account. Any differences in arousal between patients with eating disorders and controls could be partially due to their higher baseline levels of anxiety and depression (Léonard et al., 1998; Staiger, Dawe and McCarthy, 2000).
In addition, it is often difficult to get patients with eating disorders to eat foods that they consider 'forbidden', let alone get them to consume as much as non-eating disordered groups (Williamson, 1988). Simple differences in the amount eaten may directly influence psychophysiological measures independently of any pathology. One way round this may be to ask participants to imagine or to look at pictures of food, rather than consume it. However, even here it is possible that patients with anorexia may use cognitive strategies such as avoidance.
Another variable to take into account is the individualization of food cues. As Staiger and co-workers (2000) suggest, an individual's favourite binge food may elicit a greater activation than a standard food. Although some studies have used individualized favourite foods (e.g. Bulik et al., 1996; Staiger, Dawe and McCarthy, 2000) others have used standardized foods or meals (e.g. Léonard et al., 1998). In studies on psychophysiological responses to stress it can also be questioned whether the stressors used approximate to the type and severity of problems that are associated with eating disorders outside of the laboratory. For example, it is severe events and difficulties (such as the ending of a relationship) that typically provoke the onset of an eating disorder rather than being taxed by mental arithmetic or preparing a brief speech. On the other hand, laboratory studies using tasks such as these have been shown successfully to disinhibit dietary restraint (e.g. Heatherton, Herman and Polivy, 1991).
Any or all of these reasons may account for why there is very little psychophysiological research in patients with anorexia nervosa or bulimia nervosa.
Furthermore, psychophysiological measurement is very complex, involving influences due to both situational and person factors. This creates variability in the data and one of the consequences is that only very salient effects can be established using psychophysiological methods. It is also difficult to control other variables that may influence results, such as the amount of food eaten prior to the