Better pre-treatment response inhibition predicts positive treatment outcomes in trichotillomania

A recent study published in Behaviour Research & Therapy shows that better pre-treatment response inhibition in individuals with trichotillomania predicts more positive treatment outcomes, irrespective of treatment type.

Trichotillomania (TTM), a psychiatric condition characterized by repetitive hair pulling, often leads to significant psychological and functional impairments. Research has suggested that individuals with TTM exhibit neurocognitive deficits, particularly in response inhibition and cognitive flexibility. However, it remains unclear how these deficits influence treatment outcomes.

Kathryn E. Barber and colleagues investigated whether neurocognitive functioning—specifically, response inhibition and cognitive flexibility—could predict treatment response and symptom severity in individuals undergoing behavior therapy for TTM.

While behavior therapy is the standard for TTM, acceptance-enhanced behavior therapy (AEBT), which incorporates acceptance and commitment therapy, addresses internal experiences associated with hair-pulling. However, the predictive role of neurocognitive impairments in treatment outcomes remains underexplored, motivating this study.

 The study involved 88 adults (ages 18-65). Eligibility was determined based on several criteria, including a diagnosis of TTM according to the DSM-IV-TR and a minimum score of 12 on the Massachusetts General Hospital Hairpulling Scale (MGH-HS). Exclusion criteria ruled out individuals with severe psychiatric conditions, like bipolar disorder or psychosis, and those with current substance dependence. Participants were randomized into two groups: one receiving acceptance-enhanced behavior therapy (AEBT), which combines behavior therapy with principles from acceptance and commitment therapy, and the other receiving psychoeducation and supportive therapy (PST).

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Both groups attended 10 weekly therapy sessions over 12 weeks. The AEBT group’s treatment involved techniques such as habit reversal training, stimulus control, and acceptance-focused exercises to improve psychological flexibility. The PST group focused on educational topics and supportive discussions. Participants’ neurocognitive performance was measured at two points: pre-treatment and post-treatment.

The Stop-Signal Task (SST) was used to assess response inhibition, where participants had to suppress motor responses to certain visual cues. Cognitive flexibility was measured using the Object Alternation Task (OAT), which required participants to adjust their responses after receiving feedback, testing their ability to shift cognitive strategies. Of the 88 initial participants, 68 completed the entire treatment and post-treatment assessments.

Barber and colleagues found that individuals with better pre-treatment response inhibition, as measured by the SST, were more likely to respond positively to treatment, regardless of whether they received AEBT or PST. Specifically, participants with faster stop-signal reaction times at the outset of the study exhibited lower hair-pulling severity at the end of treatment. This relationship held true for both self-reported measures, such as the MGH-HS, and clinician-rated measures like the National Institute of Mental Health Trichotillomania Severity Scale. Interestingly, cognitive flexibility, measured by performance on the OAT, did not predict treatment outcomes. Perseverative errors on this task—indicating poor cognitive flexibility—were not linked to treatment success or failure.

Neither response inhibition nor cognitive flexibility significantly improved during the course of treatment. This finding suggests that while individuals with stronger baseline response inhibition were better equipped to benefit from therapy, the therapy itself did not enhance these cognitive functions. Notably, in the AEBT group, non-responders actually exhibited a decline in response inhibition, which the researchers hypothesize may be related to the older age of these participants, rather than an effect of the treatment itself.

There was also a weak but significant relationship between cognitive flexibility and clinician-rated hair-pulling severity, suggesting that individuals with poorer cognitive flexibility tended to have more severe symptoms. However, this association was not strong enough to influence overall treatment outcomes.

One limitation of the study is the lack of a healthy control group, which limits the ability to generalize changes in neurocognitive performance during treatment.

The study, “Neurocognitive functioning in adults with trichotillomania: Predictors of treatment response and symptom severity in a randomized control trial”, was authored by Kathryn E. Barber, Douglas W. Woods, Thilo Deckersbach, Christopher C. Bauer, Scott N. Compton, Michael P. Twohig, Emily J. Ricketts, Jordan Robinson, Stephen M. Saunders, Martin E. Franklin.