Does lack of sleep make things more painful?
This month, cognitive neuroscientist Duncan Astle from Cambridge University, and perceptual psychologist Helen Keyes from Anglia Ruskin University glanced over the latest neuroscience papers. Helen looked at a paper about whether how you sleep can affect how you experience physical pain the following day, and Duncan found a study linking memory recall and depression. First up, Helen told Katie about the pain study...
Helen - It's really interesting, they got 25 participants into the lab and established everybody's baseline sensitivity to thermal pain by attaching a little pad to your leg and asking you when things were painfully hot. Then these 25 people went through enforced waking where they were kept awake doing pleasant things in the lab for eight hours, and then the next morning at 8.30 AM, they were put in an fMRI scanner and their pain thresholds were again measured with those same stimuli.
And now those same 25 people came back on a separate occasion when they'd had a full night's sleep in the lab, put in the fMRI scanner again and again their pain sensitivity thresholds were measured.
Katie - So what did they find then?
Helen - They found that following acute sleep deprivation, two things happened in the brain that made you experience pain more. So first of all, the part of the brain that responds to touch and pain, the somatosensory cortex, activity there increased following acute sleep deprivation. And secondly, the part of the brain that's involved in decision making so the straitum and the insular cortex, this part of the brain usually modulates pain responses and tells your brain “don't worry about this pain”, responses there were blunted so it didn't respond so much after acute sleep deprivation.
Katie - So the brain was literally more sensitive to what may have been pain that wasn't such a big deal before?
Helen - Absolutely. In those two ways, it responded more to the pain and the bits that would dampen the pain stopped responding.
Katie - So what are the implications of this then? Because lack of sleep, even mildly so, can be very very common in everyday life.
Helen - Absolutely and the follow up study they did where they did an online study asking people about their everyday sleeping patterns using a sleep diary and their experiences of pain in the subsequent days showed exactly that. That even minor changes to your sleeping patterns led to a greater experience of pain in the subsequent days.
Katie - OK. So bottom line, what should someone take away from this?
Helen - Medical practitioners might be interested to see that actually a prescription of sleep might be quite helpful to patients who are in a lot of pain, but also our everyday habits if we're feeling quite down and quite stressed and quite in pain with things, we might be able to think back on our own lives and see whether the night before we've had enough sleep, and that could be contributing to our pain.
Katie - Perhaps take sleep a bit more seriously?
Helen - Absolutely.
Secondly, Duncan Astle delved into a paper about how memories of life events link to vulnerability to depression, and he told Katie Haylor about it.
Duncan - They followed a sample of 427 adolescents who were at elevated risk of developing depression and they followed them over a year. And at the start of the year they asked all the subjects to perform an autobiographical memory test. So subjects are given cue words and they have to use those to generate memories from their own kind of personal history. And they also assessed symptoms of depression.
The subjects were all seen again at the end of the year, and they measured the same things and they also measured cortisol, so cortisol is a hormone, so it's a way of measuring stress response in these people. Those who were better able to recall positive memories at the start of the year, at the end of the year they had reduced symptoms of depression and reduced levels of cortisol, so we think reduced stress.
The theory that the authors have is that being able to better recall positive memories helps buffer the response to stress and that's why you have reduced cortisol levels a year later and reduced symptoms of depression. And they were able to test that by comparing these relationships in people who had experienced at least one stressful life event during that year, versus those who hadn't. And these relationships were strongest in those who had experienced a stressful life event. So the positive memories became beneficial in those who had experienced a stressful life event.
Katie - Do you know if this would work for people who actually haven't had a particularly stressful life relative to people who have?
Duncan - There's no harm in trying. So the data show that it's most effective in those who experience stress. Now of course the thing is you don't know when you're going to experience a stressful life event. So the implication is that by getting practiced at recalling more positive memories, you are gradually making yourself more resilient to future stresses that could be just around the corner.
Katie - So could this be used in a clinical or psychological setting?
Duncan - Well new treatments for depression are sorely needed. And this study implicates autobiographical memory as a potential target for therapies that aim to reduce responses to stress and symptoms of depression. And actually there are other groups here in Cambridge who are working to develop new interventions that target autobiographical memory and try and train people to get better at being more flexible, and being more positive in their memory recollection, with the aim that that might help reduce symptoms of depression.
Katie - Okay. And key point takeaway from this study, what would you say?
Duncan - It's really important that we practice and become proficient at recalling positive experiences that have happened to us and that doing that is a really important part of making ourselves resilient to stressful experiences that we may encounter in the future.