Predictive Coding, Diagnosis, and the Psychology of Illness
Introduction
Have you ever noticed how the expectation of something can change how you feel in your own body? From a placebo pill that eases pain to the sudden onset of a headache after hearing that a flu is going around, our brains are never passive observers. They are active predictors, constantly writing the script for how we interpret our bodily experiences.
In The Age of Diagnosis, Suzanne O’Sullivan explores how our modern reliance on labels, tests, and medical predictions has collided with this predictive function of the brain. The result is complex. Diagnoses can bring comfort, clarity, and connection, but they can also shape the way we experience symptoms, sometimes even creating or amplifying them.
This blog takes a closer look at predictive coding, the psychology of diagnosis, and how expectation can both help and harm our wellbeing.
What is Predictive Coding?
Predictive coding is the process by which our brains make sense of the world. Instead of simply soaking up raw sensory information like a sponge, the brain is constantly comparing incoming signals with prior knowledge, memories, and expectations.
Imagine crossing the road. You don’t carefully analyse every car in the distance before stepping off the curb. Instead, your brain relies on learned patterns and predictions: cars usually slow down at crossings, traffic lights usually work. How far is the car from the crossroads, so how much time do I like have? The brain has predictions based on previous learning. These shortcuts keep you safe and efficient.
But predictions aren’t always perfect. When expectations are strong enough, they can overpower reality. In the context of health, this means fear of illness can sometimes trigger real physical symptoms, even when no disease is present.
When Fear Becomes Symptom
O’Sullivan describes how the anticipation of illness can create real bodily experiences. During the pandemic, for example, many people found themselves hyper-aware of every cough, ache, or breath. Searching the body for signs of infection heightened awareness of normal sensations, which suddenly felt ominous.
Research supports this. The mechanism of the nocebo effect – where negative expectations create negative symptoms – shows how powerful the brain’s predictions can be. If you believe a pill will make you sick, it often does. If you expect pain, your nervous system can generate it, even without injury.
Predictive coding offers an explanation: our brains are primed by fear, past experience, or medical warnings, and then interpret normal bodily signals through this anxious lens. The result? Genuine, felt symptoms, even in the absence of a clear biological trigger.
The Double-Edged Sword of Diagnosis
Labels can be deeply validating. For many, receiving a diagnosis finally provides language, understanding, and community for struggles that once felt isolating. A diagnosis can help secure treatment, reduce shame, and signal to others that what you are experiencing is real.
But diagnoses can also change how we pay attention to our bodies. Once you have a label, you may start noticing symptoms you had previously ignored. A headache becomes part of “the condition.” Tiredness feels more alarming. In some cases, this scanning and expectation can create new difficulties, reinforcing the very diagnosis meant to provide relief.
This doesn’t mean diagnoses are harmful in themselves. Rather, it highlights how labels interact with the predictive brain. They can provide both a compass and a constraint.
When Sadness Becomes a Symptom
Another theme O’Sullivan raises is how modern medicine risks pathologising normal human experiences. Sadness, disappointment, and ageing are increasingly described in diagnostic terms. While this can help some people access support, it can also set up the expectation that every dip in mood signals a disorder.
Psychologically, this matters. If we expect ourselves to always feel happy, then natural sadness feels like failure. If we believe we should never forget, tire, or slow down, then normal ageing feels like disease. Again, predictive coding means these expectations can amplify distress, creating more suffering than the original feeling itself.
The Role of Technology and Prediction
Advances in genetic testing and medical technology now allow us to identify risks long before symptoms appear. For example, someone might discover they carry a genetic predisposition for Alzheimer’s or motor neuron disease decades before any signs develop.
This knowledge can empower – offering the chance for monitoring or prevention – but it can also create psychological distress. Living with the expectation of illness can produce anxiety, hypervigilance, and even physical symptoms through predictive coding. In some cases, the fear of what might happen becomes more burdensome than the condition itself.
It’s a reminder that knowledge is powerful, but not always simple. The way information is given, understood, and integrated into a person’s life matters as much as the facts themselves.
Finding Balance: The Psychology of Uncertainty
So what can we do with all of this? The answer is not to dismiss diagnoses or stop using medical technology. These tools save lives. But it may be worth holding them alongside an awareness of how expectation and prediction shape our lived experience.
Therapeutic approaches can help here. Cognitive behavioural therapy (CBT), mindfulness-based interventions, and psychoeducation often aim to reduce catastrophic interpretations of bodily symptoms. By reframing how we attend to sensations, these therapies may interrupt the cycle of fearful expectation creating distressing physical experiences.
Equally important is cultivating compassion. It’s natural to want certainty and answers. It’s human to feel fear in the face of illness. But perhaps we can balance the benefits of labels and predictions with gentleness toward ourselves – recognising that not every sensation signals disaster, and not every sadness needs a label.
Conclusion
When it comes to health, our brains are not just passive recorders of symptoms. They are storytellers, predicting and shaping our experience in real time.
Predictive coding explains how expectations can sometimes create real symptoms, and why labels and diagnoses can both heal and constrain. It also reminds us of the importance of perspective: our biology, psychology, and environment are always intertwined.
As O’Sullivan suggests, we live in an “age of diagnosis.” The challenge is to use labels and predictions wisely – valuing the clarity they can bring, while staying aware of how they may influence the stories our brains tell us about our bodies.
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