top of page

Functional Neurological Disorder (FND) : a patient's guide

including Functional/Dissociative (non-epileptic) Seizures,  Functional Movement Disorder and other functional symptoms


Causes / Mechanisms

How has it happened? ...

Figure 1 - Contralateral hypoactivation Vuilleimie
volume knob

..Its like having a software problem rather than a hardware problem. ...

Its natural when you have a problem to ask 'Why has this happened?'


But its important with functional symptoms not to confuse the question 'Why has this happened?' with the question, 'What has gone wrong in my body to cause the symptoms?'


These are two separate questions and have two different answers.







Lets deal with the second question first - 'What has gone wrong in my body to cause the symptoms?' or 'How are the symptoms happening?'


For all of the functional symptoms described on this website, the basic answer to this is that there is a problem in the function of the nervous system.


For symptoms like weakness and movement disorder, there is a problem with the way the brain is sending messages to the body


For symptoms like numbness and pain there is a problem with the way the brain is receiving messages from the body.


During dissociative seizures or dissociative symptoms, the brain is in a trance like state, a bit like hypnosis.


We are beginning to understand the complexities of what goes wrong with the nervous system in patients with functional symptoms, especially in chronic pain.


Functional scans of the brain show which parts of the brain are active or underactive when patients have symptoms. The picture opposite, for example, shows changes in the brain in patients with functional weakness.


In chronic pain we know that many changes occur to the nervous system that can't be seen with normal scans. These changes occur at nerve endings, in the spinal cord and probably most importantly in the brain.


There are a series of processes in the nervous system which behave like tiny volume knobs. When someone is in chronic pain these little volume knobs get turned up increasing someones sensitivity to pain.

















There is much that is still not known about what goes wrong in the nervous system to cause functional symptoms, but it is not a complete mystery.


In many other neurological diseases you can see what the problem is, either on a scan, for example multiple sclerosis, or under a microscope, like Parkinsons disease


Patients with functional symptoms do not have damage to their nervous systems so its not surprising you can't see it on a scan. Instead the nervous system is not functioning properly.


If you were a computer its like having a software problem rather than a hardware problem. If you have a software bug on your computer, it might keep crashing or work really slowly. You wouldn't solve that problem by opening up the computer and looking at the components.  You wouldn't see anything if you did an x-ray of that computer.


You'd have to solve it by reprogramming the computer, working out which programs were causing the problem.


Human beings are obviously more complicated than computers. Our thoughts, behaviour, sensations and emotions are our programs.



This leads in to the next section which describes something of what might make someone vulnerable to getting functional symptoms......



Brain imaging is beginning to show us how the nervous system can go wrong in patients with functional and dissociative symptoms.,


This picture shows a SPECT scan of patients who had functional weakness and sensory symptoms on one side of their body. The scan shows that when they had these symptoms, there was a part of the opposite side of the brain which was not working properly (shown in yellow)


These types of scan show that the nervous system and brain function does go wrong in these illnesses. But it doesn't mean that you can't do anything about it


Picture from Vuilleimier et al. Brain 2001

bottom of page