استفاده از نظریه های شکل گیری توهم برای توضیح باورهای غیر طبیعی در اختلال بدریخت انگاری (BDD)

Body Dysmorphic Disorder (BDD) is characterised by overvalued or delusional beliefs of ‘imagined ugliness’. Delusional beliefs have been explained by a number of cognitive theories, including faulty perceptions, biases in attention, and corruption of semantic memory. Atypical aesthetics may also influence beliefs in BDD. In fourteen BDD patients, compared to controls (n=14), we examined these theories of beliefs in a cognitive test battery consisting of perceptual organisation and visual affect perception tasks, a Stroop task using body words, a sentence verification task, a fluency task, and an attractiveness task. BDD patients performed similar to controls on tasks measuring information (bias) processing and aesthetics. However, BDD showed abnormal abilities on semantic processing involving sentence verification and category fluency. There was only a trend finding of impaired performance on perceptual processing tasks in BDD. The findings suggest that the delusional beliefs in BDD may be explained by impaired semantic processing.

Body Dysmorphic Disorder (BDD) is characterised by severe dissatisfaction with one's appearance, with a preoccupation with ‘imagined’ or minor physical flaws. The beliefs held by BDD patients have been shown to vary in terms of the degree of conviction along a continuum from mild to severe (delusional) beliefs (Castle and Rossell, 2006 and Labuschagne et al., 2010). These delusional beliefs in BDD are usually not bizarre, but are certainly exaggerated thoughts about their physical appearance, and the conviction about unattractiveness and/or abnormality in appearance causes extreme distress and preoccupation. There is also evidence to suggest that those BDD patients with delusional beliefs show greater morbidity, which was associated with more suicidal attempts, more drug abuse or dependence and less likelihood of receiving treatment (Phillips et al., 2006). Therefore, understanding the beliefs in BDD is essential for our understanding of the progression of the disease (Castle et al., 2006). We are aware of no published study that directly investigated the cognitive processes involved in the beliefs that BDD patients have, as most studies investigating the beliefs in BDD use measures that are assessing delusional or psychological qualities rather than cognitive aspects of the beliefs. We believe that the strong beliefs held by BDD can at least in part be explained by cognitive abnormalities. Therefore, it remains unclear whether there are cognitive abnormalities that may underpin the creation of appearance-related delusional beliefs in BDD. There are a few published cognitive studies in BDD that have shown evidence of executive functioning impairments (with poor performances on tasks such as Tower of London and Stockings of Cambridge) as well as memory and learning deficits mediated by executive functioning deficits (Hanes, 1998, Deckersbach et al., 2000, Dunai et al., 2010 and Labuschagne et al., 2011). There have also been a handful of studies implicating impaired visual and perceptual abilities and biased processing in the pathogenesis of BDD. For example, emotion recognition studies (Buhlmann et al., 2002a, Buhlmann et al., 2004 and Buhlmann et al., 2006) have reported that BDD is associated with impaired facial emotion recognition abilities as well as a perceptual bias towards negative (i.e., angry) emotional face stimuli whereby they are more likely to misinterpret neutral expressions in a negative way. Similarly, a negative interpretive bias was also found in BDD patients when presented with body-related and general scenarios (Buhlmann et al., 2002b) suggesting that biased processing in BDD extends beyond that of face recognition. This evidence, together with the strong beliefs about physical appearance, suggests that perceptual and/or social processing abnormalities may be the key cognitive deficits of BDD. Interestingly, a more recent study showed that BDD patients were able to recognise emotions when presented with only the eye region of faces (Buhlmann et al., 2013). Together, we proposed that, based on the previous evidence, BDD may also be associated with perceptual integration abnormalities. A number of cognitive impairments have been related to delusional thinking including anomalous ‘faulty’ perceptions (Maher, 1988), difficulties in social cognition and emotional attributions including attentional biases (Bentall et al., 1991, Kinderman et al., 1992 and Langdon et al., 2002), aberrant semantic processing (Rossell et al., 1998), Theory of Mind (ToM) deficits (Frith, 1987 and Frith, 1992) and reasoning abnormalities (Garety, 1991). However, the vast majority of this research has been performed in patients with schizophrenia, and might or might not be applicable to other disorders such as BDD. In a pilot study (Labuschagne et al., 2011) our research group did not identify either ToM or reasoning impairments in four BDD cases; which is supported by a more recent evidence (Reese et al., 2011). We are not ruling out that ToM and/or reasoning deficits could be a part of the neurocognitive profile of BDD, however, these processes are complex and time-consuming to assess, and thus were not a focus of the current work. The current work is based on four theories of cognitive (delusional) processing that may relate to BDD. These are reviewed below. Firstly, Maher, 1974 and Maher, 1988 cognitive account of delusions and delusional thinking emphasises ‘faulty perceptions’ or an abnormality in perceptual processing which involves paradoxically ‘normal’ reasoning. That is, primary sensory inputs are disturbed and experienced at greater intensities than normal (e.g., the experience of increased vividness of colours) but the explanation, and thus the delusion, is derived via reasoning that is entirely normal (i.e., normal cognitive mechanisms). Therefore, in BDD this may relate to faulty perceptions of body-related concepts. Secondly, delusional thinking has also been associated with information processing bias. Thus, Bentall et al., 1991, Bentall et al., 1994 and Bentall et al., 2001 argued that delusions are a result of a bias in information processing, particularly that of negative events. These negative events have commonly been associated with the nature of the psychopathology such that the preferential encoding of stimuli relate to the main concern (i.e., thought-content specific bias). In the case of BDD, this supports the negative bias previously reported ( Buhlmann et al., 2002b and Buhlmann et al., 2006), and these negative events may be linked to negative thoughts and perceptions of their own bodies. Thirdly, Rossell et al. (1998) articulated a theory of semantic processing deficits in which delusions are conceptualised as resulting from a corrupt storage mechanism for semantic information, including knowledge and facts about the world as well as the meanings of words. Rossell et al. (2010) argued that the disturbance of a person's store of information (i.e., aberrant semantic processing), co-jointly with the ‘faulty perceptions’ identified by Maher, 1974 and Maher, 1988, may result in a bias in the processing of general knowledge. Considering BDD, patients may be more likely to interpret someone laughing behind them as a negative response to their appearance, and this may relate to their belief in their specific ‘abnormal’ body part, but also their belief that other people pay particular attention to their part.