Attention and Working Memory Deficits in OCD Checking Behaviour

Abstract

The evidence for memory impairments in obsessive-compulsive disorder (OCD) is mixed (Hermans et al., 2008). For example, findings are inconsistent, whether OCD have poorer memory capacity compared to neuro-typical controls, or whether verbal memory is less affected than visuospatial memory (Muller and Roberts, 2005b). Some evidence (Greisberg and McKay, 2003) pointed to a more subtle interaction with executive dysfunction leading to impaired memory performance. In a review of 58 experiments Harkin and Kessler (2011) argued that rather than classifying memory deficits in OCD by modality, for example verbal vs visuospatial, it is more instructive to classify the experiments by their task demand in terms of Executive function (E), Binding complexity (B) and memory Load (L). Using the EBL classification system in combination with the Baddeley model of working memory (Baddeley 2000) with an episodic buffer, performance in working memory tasks could be better explained in terms of task demands of executive function. For example, working memory (WM) performance of subclinical OCD checkers can be impaired if presented with irrelevant but misleading information during the retention period. The aim of this thesis was firstly, using magnetoencephalography (MEG) and a paradigm designed to provoke executive dysfunction in OCD participants, to measure the neural correlates of deficient working memory processing. Secondly, to use MEG to investigate the neural correlates of attentional bias and executive dysfunction in OCD checking behaviour when engaged in an endogenous attention (Stroop) task. Lastly, using transcranial magnetic stimulation (TMS) to target task relevant brain areas in attempt to affect beneficially the task performance of OCD checker participants engaged in an exogenous attention (Inhibition of Return) task, an endogenous attention (Stroop) task and in the working memory task. Using ecologically valid stimuli that resonate with the checkers’ OCD related concerns, the neuroimaging data revealed different patterns of activity, comparing subclinical OCD checkers with neuro-typical controls. These patterns are consistent with the stimuli provoking deficient executive function in the subclinical checkers. The brain activity recorded was consistent with repeated memory checking and poor suppression of irrelevant stimuli. Efforts to remediate executive dysfunction with TMS were only partially successful. In accord with the EBL classification system, the ecologically valid threat stimuli in combination with the WM and Stroop tasks were successful in exploiting executive dysfunction in subclinical checkers in domains of working memory and endogenous attention. Neural correlates of the impaired processing were measured successfully using MEG.