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Rumination: We've all done it before. It's that pattern of recursive thinking where you focus on your negative mood as well as the causes and consequences of it. For people diagnosed with major depressive disorder (MDD), rumination is often a big player in their disease. Rumination has been shown to prolong episodes of depression and to increase peoples' risk of developing new depressive episodes.
Because of this link between rumination and depression, scientists have been very interested in how the brains of people diagnosed with major depressive disorder (MDD) operate when they ruminate and how this compares to the brains of people without a depression diagnosis. The hope is that by understanding the neural correlates of rumination, we can arm clinicians with the best tools to diagnose and treat depression. We might also learn something about rumination and the brain in general.
Recently, researchers at Stanford University invited people diagnosed with MDD and people who were free of any clinical diagnosis (control participants) to have their brains scanned using fMRI while they performed a number of tasks designed to induce rumination. Unlike some cognitive process (e.g., moving your attention from one side of a computer screen to another), rumination is not easily observed or assessed, so the scientists had to be a bit creative in how they got people to ruminate.
While in the fMRI scanner, people were asked to do several different tasks. The first was designed to induce rumination. People were asked to "think about what people notice about your personality." Two other tasks served as control tasks, so that the scientists could pit brain activation during rumination against these tasks to see differences in neural activation between ruminative thinking and other types of thinking. In these control tasks, sometimes folks were asked to "think about what contributes to team spirit" and, other times, to "think about a row of shampoo bottles on display." The researchers reasoned that these latter two thought tasks would capture the types of abstract and concrete thinking that occur during rumination, but would be relatively free of rumination itself.
When the researchers peered inside everyone's heads to see how people's brains operated during these thinking tasks, they found some pretty interesting differences between the MDD individuals and their control counterparts. Specifically, the MDDs had greater activation than controls during the rumination task in a part of the brain called the anterior cingulate cortex. Thought to be involved in mood regulation, the anterior cingulate cortex may be infusing more emotion into the depressed individuals' ruminations than controls. Depressed individuals also had greater activation in the amygdala, that almond shaped region deep in the brain that is a major player in negative emotional reactions. Finally, and perhaps most interestingly, MDDs showed greater activation in the prefrontal cortex (DLPFC), where, as I have talked about before in this blog, our working memory (a.k.a., cognitive horsepower) is housed.
If depressed individuals spend a lot more of this neural real estate trying to regulate their thinking, they may have less brainpower left over to do other important thinking and reasoning tasks. This may explain the cognitive deficits depressed individuals sometimes show.
It's no secret that depressed individuals report greater ruminative tendencies than their non-depressed counterparts. But, rumination isn't limited to those diagnosed with depression. That's why, understanding differences in how MDDs and non-depressed individuals' brains operate during rumination may be a key to helping stave off the negative consequences of a major depressive disorder. When they ruminate, people diagnosed with MDD tend to recruit, more so than non-depressed individuals, emotion centers of the brain and also important parts of prefrontal cortex that we need to think and function at our best. Armed with knowledge about how rumination in seeded in brain, the hope is that we can moving closer to alleviating it.
For more on rumination and how it impacts performance, especially under stress, check out my book Choke.
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Cooney, R. E., et al. (2010). Neural correlates of rumination in depression. Cognitive, affective, and behavioral neuroscience, 10, 470-478.
