We’ve all had the experience of our minds getting a bit stuck on a topic – chewing it over, turning it over, and unable to let it go. Psychologists call this process “ruminating” – and while it can be helpful for a short period of time if all this thinking gives us a new perspective on issues, it’s less helpful – or even harmful – if our minds get stuck on negative thoughts about ourselves, our relationships with friends, family, and loved ones, or our life situation. Ruminating for long periods of time over topics like this is a symptom of depression – the inability to let go of negative thoughts, see the bright side, and move on to thinking about new and more positive events in life.
Why are some people able to move on from rumination and others get stuck? Scientists at Posit Science and their collaborators at Hebrew University in Israel and the Dominican University of California had an idea. They had been studying response inhibition – the brain’s ability to suppress an automatic response and make a planned response instead. Like when you see a cookie – you’re automatic response might be to pick it up and eat it – but if your response inhibition processes are working well, your brain might be able to slow down that automatic response and give yourself the time to make a planned response – perhaps grab a healthy banana for a snack instead.
In depressive rumination, the researchers thought that perhaps the brain gets stuck on certain thoughts – particularly negative thoughts in people experiencing depression – because the automatic response is to continue the depressive thinking, and the brain doesn’t have enough inhibitory control to suppress that automatic response to allow the brain to engage in new, more positive thinking.
To test this idea, the researchers worked with 119 people. Each person was given a standardized questionnaire to measure their depression symptoms (which ranged from minimal to severe), and given a computerized cognitive test of their inhibitory control. In this test, the person was shown a series of images (for example, male and female faces), and asked to press a key in response to a certain type of image (for example, female faces) and avoid pressing the key for other types of images (in this example, male faces). The researchers organized the sequence of images so that those requiring a key press (in this example, the female faces) were much more common, making the key press the “automatic” response. Researchers could then measure an individual person’s response inhibition by measuring how often they pressed a key incorrectly (in this example, to a male face).
If you’ve done BrainHQ training, this might sound familiar – it’s very similar to the Freeze Frame exercise!
The researchers found something very interesting – people who had higher levels of depressive symptoms generally had worse inhibitory control.
Then, digging into the data, they found something even more interesting. One variation of the inhibitory control test used faces that could have happy, sad, or neutral expressions. The emotional expression of the face didn’t matter for the task – but it turned out that inhibitory control deficits were larger when then faces were sad or neutral – but not if they were happy.
The data shows the depressive symptoms are associated with poor inhibitory control, and specifically that people with high depressive symptoms have a hard time suppressing their automatic responses to sad or neutral images – but they can suppress their automatic responses to happy images just fine. You can read the complete paper here if you’re interested in learning more.
This leads to a pretty interesting idea about depressive symptoms – that perhaps people get stuck in depression because the brains find it easy to automatically engage with depressive thoughts, and can’t get out of that loop.
In turn, that leads to a pretty interesting idea about treating depressive symptoms. What if we could improve inhibitory control? Particularly for images or speech or thoughts that were sad? Would that improvement in inhibitory control reduce the burden of depressive symptoms in people?
We don’t know yet, but we’re very interested in finding out. Several BrainHQ exercises – including Freeze Frame and Mind Bender – are designed to improve general inhibitory control. To figure this out, we would need a proper randomized controlled trial – comparing the effects of brain exercises designed to improve inhibitory control to an active control (perhaps ordinary video games) on depressive symptoms. I’m optimistic about the line of work, because previous studies have shown that BrainHQ exercises reduce the risk of depressive symptom worsening and the onset of depression in older adults, and other studies show that BrainHQ exercises combined with other novel brain training exercises improve depressive symptoms in people with depression. Adding exercises that target inhibitory control could strengthen these results.
In general, scientists’ ideas about the neurological basis of depression have changed enormously over the past decade. Although originally scientists thought of mood and cognitive function as very distinct aspects of brain function, it’s now become clear that the mood symptoms of depression are deeply linked with cognitive impairment – people with depression frequently suffer from poor processing speed, attention, and working memory. SSRIs – medications like Prozac and Zoloft – were originally thought to work by raising the levels of serotonin to “normal” levels, but now it’s becoming clear that they may work in part by improving brain plasticity – allowing a brain stuck in depression to reorganize itself out of depression.
This tells us we have a lot to learn about the basic biology of depression – but also a lot of reasons to hope that new science will lead to new treatments!