اختلال تصور از بدن لمسی در بی اشتهایی عصبی

Body image disturbances are central to anorexia nervosa (AN). Previous studies have focused mainly on attitudinal and visual aspects. Studies on somatosensory aspects thus far have been scarce. We therefore investigated whether AN patients and controls differed in tactile perception, and how this tactile body image related to visual body image and body dissatisfaction. The Tactile Estimation Task (TET) measured tactile body image: Two tactile stimuli were applied to forearm and abdomen, and, while blindfolded, participants estimated the distance between the two tactile stimuli between their thumb and index finger. The Distance Comparison Task (DCT) measured visual body image. Compared to controls (n = 25), AN patients (n = 20) not only visualized their body less accurately, but also overestimated distances between tactile stimuli on both the arm and abdomen, which might reflect a disturbance in both visual and tactile body image. High levels of body dissatisfaction were related to more severe inaccuracies in the visual mental image of the body, and overestimation of tactile distances. Our results imply that body image disturbances in AN are more widespread than previously assumed as they not only affect visual mental imagery, but also extend to disturbances in somatosensory aspects of body image.

The disturbed experience of body weight and shape is a central diagnostic criterion of anorexia nervosa (AN) (American Psychiatric Association, 2002): Despite their emaciated appearance, AN patients experience their body as too fat. This disturbance in body image is considered to be a key factor in the development, maintenance and relapse of AN (Killen et al., 1996, Stice, 2002, Stice and Shaw, 2002 and Keel et al., 2005). In addition body image problems are often found to persist after otherwise successful treatment (Carter et al., 2004 and Exterkate et al., 2009). Literature on body image in AN has focused mainly on attitudinal (e.g. body dissatisfaction) and visual aspects of body image (Smeets, 1997, Smeets et al., 1997, Skrzypek et al., 2001, Garner, 2002 and Farrell et al., 2005), which were found to correlate (Sunday et al., 1992, Cash and Deagle, 1997 and Benninghoven et al., 2007), implying a mutual relationship. Cash and Deagle (1997) showed that AN patients are more dissatisfied with their body than controls (d = 1.10) and that this disturbance in body attitudes is much larger than that of the visual body image disturbance (d = 0.64). Even though body image is regarded as a multifaceted concept including cognitive/affective and perceptual aspects of how one's own body is experienced (Cash, 2002 and Cash and Pruzinsky, 2002), surprisingly little is known about somatosensory aspects of body image in AN. A few studies have, however, shown that AN patients have a decreased interoceptive awareness and sensitivity. AN patients not only demonstrate a decreased ability to identify and discriminate between visceral sensations related to hunger and satiety (Fassino et al., 2004, Matsumoto et al., 2006 and Pollatos et al., 2008), but also find it difficult to recognize physiological stress symptoms such as an increased heart rate (Miller et al., 2003 and Zonnevylle-Bender et al., 2005). These findings imply that AN patients have a deficit in recognizing bodily signals, which may extend to deficits in somatosensory perception as well. Therefore, the main aim of the current study was to investigate whether AN patients suffer a disturbance in tactile body image. Previous research suggests that two forms of touch can be distinguished in the brain, primary tactile perception (such as an external object pressing on the skin) and secondary tactile perception (including metric/spatial information and requiring rescaling; Spitoni et al., 2010). We are especially interested in secondary tactile perception, because extracting metric information from the skin surface involves additional computational processing stages over perceiving mere contact to the skin (Dijkerman and De Haan, 2007 and Spitoni et al., 2010). It is thought that during these additional processing stages touched locations on the skin are linked to a mental body representation (Spitoni et al., 2010). The concept of mental body representation refers to the multiple abstract perceptual representations of the body in the brain that store information about the shape and size of body parts, their position in space and the integration of the parts into a structural whole (Paillard, 1999, Gallagher, 2005, Dijkerman and De Haan, 2007 and Serino and Haggard, 2010). It has been suggested that these mental body representations are constructed from and reciprocally influenced by input from various senses such as vision and touch (Serino and Haggard, 2010). Moreover, certain aspects of body representations may not only be influenced by bottom-up sensory input, but also by top-down cognitive, semantic and affective representations: In perception of the body or sensations on the skin, top-down information is used (Paillard, 1999, De Vignemont et al., 2005, Gallagher, 2005 and Dijkerman and De Haan, 2007). Touch is necessarily perceived in reference to the own body. Since somatosensory afferents do not provide bottom-up information about the size of a body part (Serino and Haggard, 2010), it is crucial to tap into other sources of information, providing top-down input, such as vision (Taylor-Clarke et al., 2004) or perhaps mental imagery, in order to make size estimations of tactile objects. In addition, top-down processes related to, for example, body dissatisfaction could influence and distort mental representations, making it plausible that AN patients estimate the size of external tactile stimuli in reference to a disturbed mental representation of the body. In healthy individuals it was indeed shown that after experimentally inducing a disturbed experience of the body, tactile perception of distances was altered (Taylor-Clarke et al., 2004 and De Vignemont et al., 2005). Previous work has already demonstrated that top-down processes related to body attitudes can lead to marked visual body image disturbances. For example, Smeets and Kosslyn (2001) found that AN patients' visual body image disturbance results from body size distortions in memory rather than perception (see also Kosslyn, 1987 and Smeets et al., 1999). While AN patients' visual size discrimination is undisturbed (Garfinkel et al., 1978 and Smeets et al., 1999), thinking about the self as fat (i.e. high body dissatisfaction) may cause size distortions of the visual mental body image. One proposed mechanism held that “thinking fat” activated prototypical images of fat somatotypes which interfere with the construction of a visual mental image of the body and distort it in the direction of fatness (Smeets and Kosslyn, 2001 and Mohr et al., 2007). Following this line of reasoning, we believe an investigation of body size representations within multiple modalities in AN is warranted. Therefore we specifically investigated whether AN patients demonstrate a disturbance in tactile aspects of body image, and explored how this disturbance related to body dissatisfaction and visual aspects of body image.