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You read an article about slipped discs in the evening, and the next morning your back starts acting up. A colleague tells you about the flu going around her department, and an hour later your throat feels scratchy. You really do feel these things. What remains open is whether you would have noticed them without the article or the conversation.
How far this influence can reach was studied by a research team at Imperial College London with people who had stopped taking an important medication. They had been on a statin, a widely used cholesterol-lowering drug meant to prevent heart attacks and strokes. Soon after starting, they developed complaints such as muscle pain, and they were convinced the tablets were to blame. In the study, they spent a year taking, month by month and in random order, either the real medication, tablets without any active ingredient that looked exactly the same, or nothing at all. They didn’t know which tablets they were taking at any given time.
With the dummy tablets, their complaints were almost as strong as with the statin. Some stopped partway through a month because the pain became too much, including in months when there was no active ingredient in their tablets at all. Six months after the study ended, half of them were taking the statin again.
The group was small, however, and consisted only of people who had already had bad experiences with statins. So the study doesn’t show that side effects are generally down to expectations. Anyone who links their symptoms to a medication should talk to their doctor before changing how they take it.
Medicine calls what the participants experienced the nocebo effect. It is the counterpart of the placebo effect: people who expect negative consequences can actually develop symptoms as a result. That raises a question that goes far beyond cholesterol pills. Where does pain come from when the tablet contains no active ingredient?
What the brain predicts
One answer comes from a model that has been gaining influence in research on bodily perception over the past few years. According to it, the brain constantly predicts what ought to be happening in the body and compares that prediction with the signals that actually arrive. The Belgian psychologist Omer Van den Bergh and the German psychologist Michael Witthöft, together with colleagues, have described what this means for physical symptoms. In their model, a symptom arises from both: from the body’s signals and from the brain’s expectations. Most of the time, the two match well. The weaker or more ambiguous a signal and the stronger the expectation, the more the expectation determines what we feel. The slight twinge in your back or the scratch in your throat from the beginning are exactly this kind of weak signal.
Where the expectation comes from hardly matters. Michael Witthöft and James Rubin at King’s College London studied what a single TV report can do. Some participants watched a documentary about the supposed health risks of Wi-Fi, the others a segment on data security. Afterwards, everyone sat for fifteen minutes next to a Wi-Fi transmitter that was actually switched off. More than half then reported symptoms they attributed to the signal, such as difficulty concentrating. The alarming documentary amplified the symptoms in those who had been more anxious to begin with.
How well we actually sense our bodies
You might think that people who know their bodies well would be safer from this kind of deception. A team led by the neuroscientist Sarah Garfinkel at the University of Sussex asked people to count their heartbeat without feeling their pulse, and also asked how well they thought they perceived their own body. The two were only loosely connected. People convinced that they knew their bodies well didn’t automatically count more accurately. Belgian researchers led by Olivier Desmedt also found evidence that many people, when doing this task, factor in how many beats they would expect, for example because they know their resting heart rate. So even with our heartbeat, what we believe we know about our body plays a part.
According to the model by Van den Bergh, Witthöft and colleagues, attention also plays a role. If you listen inward with worry and search for possible symptoms, you are more likely to notice sensations that fit that worry, and you may experience them more strongly. Whether people with particularly fine bodily perception are more susceptible to nocebo effects has not yet been settled.
A bodily signal therefore often allows for more interpretations than it seems to at first. Whether you dismiss the pressure in your head, which you genuinely feel after a short night, as tiredness or register it as a warning sign also depends on what you were expecting. As long as that expectation runs unnoticed in the background, you can hardly check it.
Exercise: Feel first, then interpret
Two small steps can make these expectations visible. In the first, you test right now how reliable your sense of your own heartbeat is. The second you take with you into the coming days, for the moment when a bodily sensation worries you.
Sit down quietly and count your heartbeat for thirty seconds without feeling your pulse and without looking at your smartwatch. Then rate on a scale from zero to ten how confident you are. Next, feel your pulse at your wrist and count for another thirty seconds. Compare both numbers with your rating. Were you very confident and far off, or unsure and close? The result is not a health test, and a single measurement tells you little.
If you notice a bodily sensation over the next few days that worries you a little, take a minute before you interpret it. Describe to yourself in plain words where exactly you feel it and whether it presses or pulls. Then ask yourself what you were expecting and where that expectation comes from, for example a short night or an article about an illness. Jot down both in two or three keywords.
This exercise doesn’t replace a medical assessment. New, severe or persistent symptoms belong in a doctor’s hands. If you notice warning signs such as chest pain, sudden shortness of breath, paralysis or difficulty speaking, call 112 or your local emergency number immediately.
Which bodily sensation do you almost always interpret the same way, and when did you last check that interpretation?
Sources
Wood, F. A., Howard, J. P., Finegold, J. A. et al. (2020). N-of-1 trial of a statin, placebo, or no treatment to assess side effects. New England Journal of Medicine, 383(22), 2182–2184. DOI: 10.1056/NEJMc2031173
Van den Bergh, O., Witthöft, M., Petersen, S. & Brown, R. J. (2017). Symptoms and the body: Taking the inferential leap. Neuroscience & Biobehavioral Reviews, 74, 185–203. DOI: 10.1016/j.neubiorev.2017.01.015
Witthöft, M. & Rubin, G. J. (2013). Are media warnings about the adverse health effects of modern life self-fulfilling? An experimental study on idiopathic environmental intolerance attributed to electromagnetic fields (IEI-EMF). Journal of Psychosomatic Research, 74(3), 206–212. DOI: 10.1016/j.jpsychores.2012.12.002
Garfinkel, S. N., Seth, A. K., Barrett, A. B., Suzuki, K. & Critchley, H. D. (2015). Knowing your own heart: Distinguishing interoceptive accuracy from interoceptive awareness. Biological Psychology, 104, 65–74. DOI: 10.1016/j.biopsycho.2014.11.004
Desmedt, O., Luminet, O. & Corneille, O. (2018). The heartbeat counting task largely involves non-interoceptive processes: Evidence from both the original and an adapted counting task. Biological Psychology, 138, 185–188. DOI: 10.1016/j.biopsycho.2018.09.004
