Joormann et al. make some observations on 'sticky thoughts.' I've edited their abstract a bit:
Cognitive inflexibility may play an important role in rumination, a risk factor for the onset and maintenance of depressive episodes. In the study reported here, we assessed participants’ ability to either reverse or maintain in working memory the order of three emotional (positive or negative) or three neutral words. Differences (or sorting costs) between response latencies in backward trials, on which participants were asked to reverse the order of the words, and forward trials, on which participants were asked to remember the words in the order in which they were presented, were calculated. [A recognition probe was used to index sorting costs (i.e., differences between response latencies on the forward and the backward trials. The probe word consisting of one of the three words was presented until the subject responded. Participants were instructed to press a key (“1,” “2,” or “3”) to indicate as quickly and as accurately as possible whether the probe was the first, second, or third word (counting forward or backward, as appropriate) in the set they had been instructed to remember.] Compared with control participants, depressed participants had higher sorting costs, particularly when presented with negative words. It is important to note that rumination predicted sorting costs for negative words but not for positive or neutral words in the depressed group. These findings indicate that depression and rumination are associated with deficits in cognitive control.