BACKGROUND: Previous studies have shown that lesions in the anterior limb of the internal capsule contribute to obsessive-compulsive symptoms in patients with refractory obsessive-compulsive disorder (OCD). However, few reports have addressed the effects of lesions in the anterior limb of the internal capsule on cognition, learning, and memory functions in patients with refractory OCD.OBJECTIVE: To investigate the degree of damage to memory tasks in refractory OCD patients following lesions to the anterior limb of the internal capsule. DESIGN, TIME AND SETTING: A case-controlled, observational study was performed at the Department of Functional Neurosurgery, Ruijin Hospital, Shanghai Jiao-Tong University, China from May 2007 to March 2008. PARTICIPANTS: A total of 10 refractory OCD patients were admitted to the Department of Functional Neurosurgery, Ruijin Hospital, Shanghai Jiao-Tong University, China from May 2007 to March 2008 and were recruited for this study. The OCD patients were of equal gender, with an average age of (25.1 ± 9.6) years. An additional 10 healthy volunteers were enrolled from a community of Shanghai City as controls; they were of equal gender and aged (25.1 ± 8.6) years. METHODS: A total of 10 refractory OCD patients were subjected to lesions in the anterior limbs of the bilateral internal capsules. Wechsler Memory Scale-Chinese Revision (WMS-CR, as a task of explicit memory) and the Nissen Version (serial reaction time task) software (SRTT, as a task of implicit memory) were applied to determine memory functions and learning performance in pre- and post-operative OCD patients and controls. MAIN OUTCOME MEASURES: WMS scores, reaction time in SRTT, and Yale-Brown obsessive compulsive scale scores were measured in pre- and post-operative OCD patients and controls. RESULTS: Compared to controls, the pre-operative OCD patients exhibited reduced memory task scores (P = 0.005), whereas scores for reciting numbers of backwards digits were greater (P = 0.000). Figure recall and associative memory were less in OCD patients at 1 week following surgery than in the pre-operative OCD patients (P = 0.042, P = 0.002, respectively). Reaction time in implicit SRTT was significantly longer in pre-operative OCD patients compared with controls and post-operative OCD patients (P = 0.01, P = 0.03, respectively). These results suggested ameliorated SRTT following neurosurgery. Yale-Brown Obsessive Compulsive Scale results revealed significantly improved OCD following lesions in the internal capsule (P = 0.04). Some post-operative OCD patients suffered from deficits in short-term memory and implicit memory. CONCLUSION: Lesions in anterior limbs of bilateral internal capsules improve obsessive- compulsive symptoms and implicit memory in OCD patients, but result in aggravated short-term memory deficits.