Individual differences in working memory capacity and distractor processing: Possible contribution of top–down inhibitory control

Working memory capacity (WMC) represents proficiency in allocating limited attentional resources. Previous studies on individual differences in WMC have shown that high WMC subjects have a superior ability to inhibit goal-irrelevant information, while low WMC subjects have difficulty in inhibiting such information. The present study aimed to reveal the neural structure that differentiates the inhibitory ability between subjects with high and low WMC. In the present fMRI study, activities of the bilateral inferior frontal gyrus (IFG), the fusiform gyrus (FFG) and the left middle frontal gyrus (MFG) were measured while participants were engaged in a face working memory task with distraction. Behavioral results showed that the performance of high WMC subjects was superior to low WMC subjects. As expected, the bilateral IFG showed greater activation in the stronger distraction condition; however, the magnitude did not differ between WMC groups, suggesting that the IFG functions to inhibit intensive distractors, but appears to be independent of the individual differences in inhibitory ability. On the other hand, the activation of the bilateral FFG in the low WMC group was stronger than in the high WMC group, while the activation of the left MFG was stronger in the high WMC group than in the low WMC group. These results indicate that the superior inhibitory ability in high WMC subjects may depend on the efficient top–down modulation from the left MFG to the posterior perceptual areas.