Anorexia nervosa and bulimia nervosa were linked to different neuropsychological impairment. However, the findings in the previous studies were not consistent, included non-specific deficits in different cognitive functions and were as such difficult to interpret. On the other hand, there was increasing evidence, that anorexia nervosa is closely related to some personality characteristic, such as perfectionism and compulsivity. Furthermore, obsessive-compulsive personality was found to be possible risk factors for their development (Anderluh et al, 2003).
Our hypothesis was that neuropsychological deficits in eating disorders mirror the behavioural and personality characteristics of obsessive-compulsive type. A battery of neuropsychological tests that measure different aspects of cognitive inflexibility was selected, which included Trail Making B test, Brixton test, Verbal Fluency test, Haptic Illusion test, a Cognitive Set Shifting test and a Visual Set test. Four of these tests include the conceptual shift component, in one a perceptual inflexibility is tested and in additional test of dysdiadodokinesis was added that tracks a soft neurological dysfunction of the motor system.
In the first part, three groups were testing using this battery of tests, a group of people with acute anorexia nervosa, with acute bulimia nervosa and a healthy control group. Measures from the tests clustered into four factors: simple alteration, mental flexibility, preservation and semantic shifting. The anorexia nervosa group showed global impairment on three of four factors, compared to healthy controls, while patients with bulimia nervosa experienced impairment in a more selected areas that present a cognitive set shifting dysfunction. This supports the previous studies that showed cognitive dysfunction as a common feature of anorexia nervosa (Strupp et al, 1986, Maxwell et al, 1984, Braun et al, 1992, Tchanturia et al, 2001, Tchanturia et al, 2002), as well those that reported finding of a soft neurological sign of dysdiadodokinesis in people with anorexia nervosa (Gillberg et al, 1994, Rastam, 1992).
In the second part, patients with acute anorexia nervosa were compared to the group of patients with anorexia nervosa soon after the weight restoration and to the fully recovered patients that were without any symptom of the disease for at least a year. While recovered patients showed better performance than weight restored or acutely ill patients, their performance on tests that cluster into perceptual set shifting factor and preservation factor persisted to be significantly worse than in healthy control group. This results confirm the prediction that at least some aspects of cognitive inflexibility persists after weight restoration and full recovery and thus possible presents a vulnerability factor for eating disorders.
In the third part, performance on the selected cognitive tests was correlated to the measured level of current obsessive-compulsive symptomatology, as well as obsessive-compulsive personality in childhood before the onset of an eating disorder. Interesting, cognitive inflexibility as measured by selected tests, was found to correlate with both measures of obsessive-compulsive personality. The temperamental features may thus together with deviation of cognitive flexibility presents an underlying and possible vulnerability factor for eating disorders.
Our findings suggest that cognitive inflexibility may present an important manifestation of biological substrate of anorexia and bulimia nervosa and may add to the broader phenotypic definition for future genetic studies. Furthermore, our neuropsychological model stresses the importance of cognitive impairment in eating disorders and offers additional confirmation that eating disorders may present neurodevelopmental disorders, similar to other complex psychiatric illness, such as for example schizophrenia. It also offers new areas for therapeutic intervention, which can importantly contribute to the higher efficiency of the treatment strategies in anorexia nervosa, the disease which today still lacks successful treatment approaches. First treatment interventions based on the enhancement of cognitive flexibility are underway as part of our next research projects.