STOPPING OF TASK-SWITCHING IN PATIENTS WITH OBSESSIVE-COMPULSIVE DISORDER (OCD)

Abstract

Introduction Inhibition and attentional switching both play central role in theorizing about cognitive impairments in OCD. The aim of the present study was to investigate inhibition and shifting abilities within a single experimental task. A new ‘inhibition-of-switching’ task was designed with minimal memory load suitable for patients under medication. The goal of this task was to simulate a real life situation, where following consecutive successful execution of a simple algorithm, participants need to change to another algorithm in order to respond adequately to new stimuli configurations. However, a further difficulty could be if the response must be inhibited for the same stimuli configuration on the next encounter with it. We hypothesized that OCD patients along with slower switching performance, will have difficulties in inhibiting previously adequate switching responses, making more false alarm type errors. Methods Twenty-six properly diagnosed OCD patients and twenty-six healthy adults matched in age and education undertook an inhibition-of-switching task in two conditions. 1) Single task condition: two digits appeared on a computer screen, and subjects had to press the right or the left-arrow key under the bigger number, and 2) Secondary task conditions: here the participants’ primary task was identical with the single task condition, whereas their secondary task was to press the up-arrow key if the two presented digits were identical. Furthermore, participants had an inhibition rule for the secondary task, they needed to respond only on every second time encountering with identical digits. To assess the memory performance, subjects completed the Digit Span Forward and Backward Tasks and the Prospective Retrospective Memory Questionnaire (PRMQ). Statistical analyses were performed using mixed analysis of variance and two-tailed t-tests. Results We found that secondary task instruction produced significantly more cost in terms of reaction time during the execution of primary task for OCD patients compared to a healthy control group. However, there was no difference in switching cost in terms of reaction time between the two groups, suggesting that OCD patients had no difficulty with changing one stimuli-based response algorithm to another one. Additionally, OCD patients made significantly more false alarm type errors in the secondary task, and there was a significant positive correlation between the number of false alarm type errors and the prospective memory subscale scores of the PRMQ in the OCD group. Conclusion These results suggest that OCD patients experience difficulties during inhibition-of-switching task, and here we propose that these difficulties originate from over-monitoring of secondary task stimuli during execution of primary task and disinhibition of activated out-of-date responses. We argue that over-activated intentions go together with a response inhibition deficit, and these two factors together contribute to the higher rate of perseverative errors.