One of the worst things about depression is the intrusive, depressive thoughts that stay around like they have nowhere else to be. The are persuasive and powerful and they pollute the filter through which the rest of the world is experienced.

A new study published in the Journal of Affective Disorders has shown that the tendency of depressive thoughts to play over and over, leaves little room for any positive thoughts or memories. This affects memory and makes way for depressive thoughts to expand and tighten their grip. The findings are important for shining further light on the relationship between depression and memory, as well as the progression of depression over time.

‘We have known that negative thoughts tend to last longer for those with depression. However, this study is unique in showing that, these thoughts, triggered from stimuli in the environment, can persist to the point that they hinder a depressed person’s ability to keep their train of thought.’ Bart Rypma, PhD, Center for BrainHealth principal investigator.

The Research. What they did.

The study involved 75 participants. 30 of those participants had depressive symptoms and 45 of them did not. Each participant was asked to respond to a sentence that was built around a depressive thought or neutral information. The depressive sentences included, ‘I am sad’, or ‘People don’t like me’. Once participants had responded to the sentence, they were asked to remember a series of numbers.

What they found.

The negative sentences influenced the amount that people with depression could remember. When people with depression were given the negative thought first, they remembered one-third less number strings than people without depressive symptoms. Their performance in the memory task improved when they were exposed to the numbers before the depressive message.

Why depressive thoughts are so enduring.

This finding helps to make sense of a few things. We know that depression swipes at a person’s ability to concentrate or remember things in their day to day lives and this research offers an explanation as to why.

There is a limit to what we can hold in memory at any given point in time. When this space is occupied by persistent, intrusive depressive thoughts, there is little room for very much else. When there is no space for positive thoughts, the depressive thoughts that have already taken up precious mental real estate are able to flourish. As a result, memory, concentration, or the capacity to think more positive thoughts is compromised.

‘The fact that depressive thoughts do not seem to go away once they enter memory certainly explains why depressed individuals have difficulty concentrating or remembering things in their daily lives. This preoccupation of memory by depressive thoughts might also explain why more positive thoughts are often absent in depression; there simply is not enough space for them.’ – Lead author, Nick Hubbard, doctoral candidate at the Center for BrainHealth.

With a vast amount of mental resources being recruited by depressive thoughts, there is a diminished capacity to make way for positive thoughts. Heads are fertile ground for thinking and when the balance of negative thoughts and positive thoughts is out, the negative ones will take over. The positive thoughts will become less, the depressive thoughts will take over.

The finding that depressive thoughts linger in memory and interrupt future thoughts and memories might be a vital clue to understanding how depression maintains over the course of a person’s life. When there is limited room available, and limited opportunity for nourishing thoughts to occupy the space that’s there, pulling out of a depressive cycle will be difficult.

Depression is not all about negative thoughts. Negative thinking is a symptom of depression, and it may help to maintain the symptoms, but we are far from understanding their role in contributing to the initial symptoms. Although there we are moving closer to an understanding of depression, we still don’t understand what makes a mind vulnerable to these depressive thoughts in the first place. What we do know is that once they find their way in, they will thrive.

Depression is a debilitating illness and there is no easy fix. The more we can understand about it, the more targeted the push against it can be. Relief from the symptoms will come in different ways for different people.

The authors highlight the benefits of mindfulness in empowering people with depression to recognise and influence the content of their depressive thoughts. Mindfulness has been shown to be as effective as anti-depressants for many people in the prevention of relapse, and this research starts to explain why.

Negative thoughts often begin automatically and persist automatically. They don’t need very much fuel at all to flourish. Mindfulness shines the light on them and brings them into the open. This will start to weaken their stronghold, either by diluting their concentration with positive thoughts, or by decreasing their direct impact.