Elsevier

Biological Psychiatry

Volume 61, Issue 3, 1 February 2007, Pages 330-336
Biological Psychiatry

Original article
Functional Magnetic Resonance Imaging Study of Regional Brain Activation During Implicit Sequence Learning in Obsessive–Compulsive Disorder

https://doi.org/10.1016/j.biopsych.2005.12.012Get rights and content

Background

Corticostriatal circuitry has been implicated in the pathophysiology of obsessive–compulsive disorder (OCD). The serial reaction time (SRT) task, a paradigm that tests implicit sequence learning, has been used with imaging to probe striatal function. Initial studies have indicated that OCD patients exhibit deficient striatal activation and aberrant hippocampal recruitment compared with healthy control (HC) subjects. Here, we used the SRT and functional magnetic resonance imaging (fMRI) to replicate prior results in a larger sample and to test for relationships between regional activation and OCD symptom dimensions.

Methods

Using SPM99, fMRI-SRT data from 12 OCD and 12 matched HC subjects were analyzed. Symptom dimensions followed a four-factor model scored on a 0- to 10-point scale.

Results

For the implicit learning versus random contrast, group by condition interactions revealed aberrant recruitment within the hippocampus as well as orbitofrontal cortex (OCD > HC) but no striatal group differences. However, an inverse correlation was found between striatal activation and specific symptom factors.

Conclusions

These results replicate previous smaller studies showing aberrant hippocampal recruitment in OCD during SRT performance. Although findings of deficient striatal activation in OCD were not replicated, correlation results suggest that this inconsistency may be attributable to differences among OCD symptom dimensions.

Section snippets

Subjects and Clinical Assessments

Written informed consent was obtained from all subjects before enrollment; this study was approved by the Partners Human Research Committee. Data are reported from 12 subjects with OCD and 12 HC subjects who were group-matched for gender (8 women, 4 men), age [(mean ± SD) OCD: 28 ± 5.66 years; HC: 27 ± 6.61 years; t(22) = .40, p = .69], and years of education [OCD: 15.33 ± 1.56 years; HC: 16.67 ± 2.46 years; t(22) = –1.58, p = .13]. All subjects were right-handed (Oldfield 1971) and were

Subject and Data Selection

Sixteen OCD and 40 HC subjects were initially tested. Six HC and two OCD subjects were excluded because of scanner errors. Four HC and one OCD subject were excluded because of explicit contamination (> 6 consecutive correct responses on the debriefing task). One OCD subject was excluded because of excessive motion. Twelve of the remaining 30 HC were selected, blind to individual fMRI or other behavioral data, to best match the age, gender, and educational level of subjects in the OCD group.

Discussion

These findings represent the third report, in entirely independent samples, showing aberrant hippocampal recruitment during implicit sequence learning in OCD versus healthy comparison subjects, in the absence of significant differences in behavioral indices of learning. This confirms prior findings and extends the results to a larger cohort of subjects, including both genders. Unlike the two previous reports, however, here we did not find a significant decrement in activation within right

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