Elsevier

Biological Psychiatry

Volume 58, Issue 3, 1 August 2005, Pages 239-244
Biological Psychiatry

Original article
Implicit Sequence Learning in Obsessive-Compulsive Disorder: Further Support for the Fronto-Striatal Dysfunction Model

https://doi.org/10.1016/j.biopsych.2005.03.045Get rights and content

Background

Obsessive-compulsive disorder (OCD) is conceived as a disease that implicates dysfunctions in fronto-striatal brain systems. According to this model, performance deficits observed in patients with lesions in these brain areas are hypothesized to be present also in OCD patients. Implicit procedural learning, which refers to the acquisition of motor or nonmotor skills by practice, is one candidate function to test this prediction.

Methods

The serial reaction time task was used to assess implicit sequence learning of 33 patients with a diagnosis of OCD and 27 healthy control participants. In addition, explicit (i.e., conscious) knowledge of the sequence was determined. A subgroup of 24 patients was reassessed after intensive cognitive-behavioral psychotherapy.

Results

Implicit sequence learning was significantly reduced in the OCD group by 41%, while explicit learning and verbal abilities were unaffected. The deficit remained stable across time, although symptoms remitted substantially. Depressive symptoms did not account for the finding. Partial explicit knowledge of the sequence was not a predictor of the amount of implicit learning.

Conclusions

Reduced implicit learning appears to be a dissociable trait of OCD patients. The results confirm previous findings and add supportive evidence for the fronto-striatal dysfunction model of OCD.

Section snippets

Participants

Forty-one patients with a diagnosis of obsessive-compulsive disorder and 36 healthy control subjects participated in this experiment. The OCD patients were recruited from consecutive admissions to the Psychosomatic Hospital at Windach, Germany. They were diagnosed according to the criteria of the DSM-IV by consensus of a psychiatrist and an experienced clinical psychologist. These clinicians were not involved in conducting the experiments or in data analysis. Diagnoses were established on the

Results

All subjects performed the task well. Response errors were rare (mean values <2%). In Figure 1, group mean values of the individual median reaction times for each of the five trial blocks are displayed showing the expected pattern of decreasing reaction times over the first four regular blocks and a sharp increase of reaction times during the randomized sequence in block 5. A 2 (groups) × 5 (trial blocks) analysis of variance (ANOVA) for repeated measurements (using Greenhouse-Geisser

Discussion

The present results confirm the hypothesis that obsessive-compulsive disorder is associated with a reduced capacity for implicit learning of location sequences. This is the first report of disturbed serial reaction time task performance in OCD under single task conditions. Previous studies have used a dual task design (Deckersbach et al 2002) or adaptations of the SRTT during brain imaging studies (Rauch et al 1997, 2000). Dual task conditions, however, impose additional demands on the

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