Interference control in working memory : neurobehavioral properties and age differences

This doctoral thesis aimed to investigate the basic processes of interference control (IC) in working memory (WM). We sought to unravel some of the underlying mechanisms of IC by examining brain correlates, while also trying to understand the differences that arise with advancing adult age. The major findings from these studies are summarized below. Study I. This study consisted of four separate experiments, with different participants in each. Three different versions of the recent-probes task was used to test the effects of a high- compared to a low-interference context on behavioral and neural measures. A combined analysis of all experiments showed that a high-interference context improved performance, both reaction times and accuracy, on the other trial types within the same task. Neuroimaging results revealed greater engagement of inferior frontal gyrus, striatum, parietal cortex, hippocampus, and midbrain in participants performing the task in the high- than participants in the low-interference context. Study II. This study compared groups of older and younger adults to examine age effects of interference control. A verbal 2-back task including proximal and distant lures revealed that older adults were more affected by interference overall, for both proximal and distant lures. Whereas younger adults overcame and were no longer affected by interference beyond 5-/6-back lures, older adults were still highly affected at the most distant 9-/10-back lures. Study III. This study expands on study II by examining brain activity during successful interference control, using a similar task setup. Proactive interference and brain activity in bilateral inferior frontal gyrus and dorsal anterior cingulate cortex declined with increasing lure distance. This decline in relevant brain regions was coupled with an increase in brain activity in left anterior hippocampus. In addition, each successfully resolved lure trial was divided into two groups, those that influenced performance negatively and those that did not. A whole brain analysis showed greater brain activity in bilateral inferior frontal gyrus, bilateral middle frontal gyrus, and dorsal anterior cingulate gyrus for the lure trials that took longer time to respond to accurately. Study IV. This study used four-year follow-up data from the Betula study to examine whether prefrontal brain volumes can be linked to the ability to control interference. Individuals were separated with respect to their ability to con