Dokument

Summary:
Trichotillomania (TTM) is characterized by repetitive hairpulling which causes significant distress or functional impairment. Currently classified as an impulse-control disorder, TTM has also been categorized as an obsessive-compulsive spectrum disorder based on phenomenological and neurobiological similarities with obsessive-compulsive disorder (OCD). In OCD numerous studies indicate cognitive dysfunctions such as an impaired ability in inhibiting thoughts and deficits in executive functions. Research on cognitive functioning has proven fruitful in identifying mechanisms underlying the etiology and maintenance of mental disorders. Although this knowledge has successfully been integrated in treatment concepts (e.g., in phobias and OCD), cognitive functioning has rarely been investigated in TTM. The current thesis, thus, aims to investigate whether TTM is characterized by cognitive dysfunctions, and if so, whether these deficits are disorder specific. Based on its clinical picture, it is important to investigate (1) the ability to voluntarily control impulses in TTM. Furthermore, on the basis of the presumed similarities between TTM and OCD, it is conclusive to investigate (2) the ability to intentionally inhibit cognitions, and (3) the integrity of executive functions. (1) We investigated motor inhibition in TTM and OCD, two disorders characterized by repetitive, intentionally performed behaviors. Performance in a GoNogo experiment of 25 TTM and 21 OCD participants was compared to the performance of 26 HC participants. In contrast to OCD and Healthy Control (HC) participants, TTM participants tended to perform either 'fast and inaccurate' (indicating poor motor inhibition) or 'slow and accurate'. TTM participants with poor motor inhibition performance reported a significantly earlier age at TTM onset than those TTM participants who performed well. There was no evidence for motor inhibition deficits in OCD. Based on our data, a subgroup of TTM sufferers seems to be characterized by motor inhibition deficits. (2) Cognitive inhibition was investigated in 21 TTM, 21 OCD and 26 HC participants using a block cued directed forgetting task. After encoding a word list, participants were instructed to intentionally FORGET these words and to REMEMBER another word list. Both lists equally included negative TTM-related and neutral words. A superior free recall of REMEMBER versus FORGET words suggests intact cognitive inhibition. The performance of OCD participants indicated a specific deficit in inhibiting the retrieval of information with a negative valence. In contrast to TTM and OCD participants, HC participants were rather inattentive to negative information. In conclusion, although cognitive functioning abnormalities were found in both disorders, cognitive inhibition deficits appear specific to OCD. (3) Few studies have compared neuropsychological functioning in TTM and OCD. In OCD, most studies suggest abnormal visuospatial abilities, memory, and executive functioning. We compared 23 TTM, 21 OCD and 26 HC individuals on neuropsychological tasks assessing these abilities. TTM participants showed increased perseveration on the Object Alternation Task suggesting difficulties with response flexibility. OCD participants showed impaired ability to learn from feedback on the Wisconsin Card Sorting Test. Other executive functions, as well as memory and visuospatial abilities were unimpaired in TTM and OCD. Our data suggest that TTM and OCD are characterized by different patterns of neuropsychological dysfunction. The current data suggest that TTM is characterized by particular cognitive dysfunctions. Unlike in OCD and HC individuals, in TTM individuals response flexibility seems to be impaired and the ability to intentionally inhibit motor actions appears to depend on impulsivity as a personal characteristic. There is preliminary evidence that TTM individuals characterized by difficulties in impulse control of motor actions have a significant earlier TTM onset than their 'non-impulsive' counterparts. In contrast to OCD, TTM does not seem to be characterized by impairments in the intentional inhibition of thoughts. Both, TTM and OCD, however, might be less inclined than HC individuals to ignore information with a negative-valence, which might be a rather general characteristic of emotional disorders. The current findings suggest that cognitive dysfunctions seem to play an important role in TTM.

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