Functional Symptoms

What are functional symptoms?

'Functional' symptoms refer to physical or mental symptoms that are not associated with any damage to the body or brain, and can occur in any medical domain, such as cardiac (e.g., chest pain or tightness), gastrointestinal (e.g., abdominal pain) or – very commonly – neurological (e.g., paralysis, numbness, stiffness, non-epileptic seizures, loss of vision, loss of voice, etc). 

What causes functional symptoms?

An excellent guide to functional neurological symptoms for patients and families is here: https://neurosymptoms.org/ - including the pages explaining what we do and don't understand about why and how they happen. Often (but not always) functional symptoms have relationships to stress (which usually makes them worse) and also attention (e.g., distraction can improve the symptom, or, the symptom itself seems to relate to dissociation - i.e. impaired attention). They also relate to one's beliefs and expectations about the symptom: e.g., the more someone expects the symptom to happen, the more it is likely to happen.

To understand these symptoms better, it helps to understand a bit about how we think the brain works. When I first studied neuroscience 25 years ago, people generally thought that the brain was a kind of information processor, that took in sensory information from the body, figured out what it meant, then decided on its goal, calculated what action it needed to take to get there, and then released a motor command. And so on and so on. 

This 'information processor' idea of the brain has now been replaced by a 'predictive model' idea. The key difference is that the 'predictive model' brain is really a model of the world (including one's own body) that is constantly making predictions about what will happen next (in one's body and in the environment). These predictions are then refined by the information coming from the senses.

The first key point is that what we perceive strongly relates to this top-down (but not 'conscious'), active process of prediction, rather than a more passive processing of sensory information. This includes what we perceive about our own bodies. 

The second key point is that sometimes these predictions are not correct! We have all (probably numerous times) felt our mobile phones vibrate in our pockets and then inspected them and discovered they were never vibrating at all. That vibration perception happened because we are (unconsciously) expecting that our phones will ring at some point, and sometimes some sensory input will activate that expectation, and you'll perceive a non-existent vibration. 

Now, imagine that you felt that vibration, and instead of checking your phone and finding it never went off, you decided it must have been ringing. This would set up an expectation that the other person might call back soon. So in the near future, you would be even more likely to perceive another vibration. Now imagine this happened every day, several times a day. You would develop a strong expectation that this vibration would happen repeatedly, and you would be looking out for it. This is roughly how we think some functional symptoms develop - an initial event sets up or reinforces an expectation about a symptom, that is then built up over time.

What is harder to understand is how this could apply to motor symptoms, not just sensory symptoms. Surely movements are active and planned consciously, unlike sensations? Well, this is not necessarily true. Many movements are automatic and happen without us thinking about them. We think that motor symptoms come about in this way - sculpted and enhanced by expectations and attention, just like sensory symptoms.