How do memories form and why do some memories become extraordinarily painful? We have all heard about conditions like post-traumatic stress syndrome, where traumatic memories linked with painful and distressing emotions cause real and disabling distress every time they are recalled. Have you ever been tempted to banish some of your memories into oblivion? The film ‘Eternal Sunshine of the Spotless Mind’ explored what might happen if we were able to selectively erase some of our painful memories. The consequences were not always as positive as expected.
But what about musculoskeletal pain? Does memory play a part in establishing chronicity in chronic pain? Some of the recent research on Fibromyalgia Syndrome (FMS) using fMRI seems to support the theory that painful stimuli can become ‘amplified’ in the brain and form inappropriate linkages with fear and emotion centers in the brain. These are the sort of links that would normally only be made with really severe painful stimuli such as a life threatening injury. Now, it has to be admitted that brain imaging studies in FMS are small and the findings can easily be disputed – but what if they were correct and point to a serious distortion of the interpretative neural matrix in the brain? We all have an ‘interpretative filter’ for sensory signals in the brain – the mechanisms by which the brain ‘triages’ the incoming signals into normal everyday stuff we can safely ignore and the sort of warnings that we really need to worry about.
So – what if part of the problem with FMS was that exercise has become inextricably linked with negative memories? We know that the opposite can occur: healthy people who exercise may get an ‘endorphin buzz’ that gives them a natural ‘high’ after exercise that makes them want to do it again. People who enjoy competing get a competition ‘high’ that makes them want to have another go. Are we prepared to put up with more pain if we have a strong memory of the ‘gain’? Can there be a polar opposite to ‘psychological dependence’?
Some of my patients with FMS previously enjoyed exercise and had been very fit before something happened to them. FMS patients will often recall having gone out for a walk and becoming so disabled by pain that they couldn’t get home again – this sort of negative memory seems to set up a fear of exercise and a conviction that exercise is unhelpful.
There are two interesting lines of research that could spell hope for patients with FMS. One was highlighted in an article by Jonah Lehrer in Wired magazine called ‘The Forgetting Pill’. Now I hasten to add that the drug in question has so far only been trialled in mice and is a very long way from being used in humans – but it highlights an interesting direction of research that may eventually have major benefits. The basic idea is that deep-seated memories are constantly being remolded in a process that involves neurons creating new linkages through protein synthesis. A Neurologist David Sactor from Columbia University has discovered a form of Protein Kinase C called PKM zeta that is crucial to this process. He and colleagues have developed a PKM zeta inhibitor ‘ZIP’ which has been shown to cause selective erasure of unpleasant memories in rats. Yes, rats. And by the way, ZIP had to be injected into the rats’ brains. So at the moment the only people likely to be planning to use ZIP will be evil dictators. But it is an intriguing idea and the concept that you only have to recall a memory to raise the possibility of changing the nature of the memory is an important one. Professor Alain Brunet from McGill University has conducted successful trials using Propranolol (an established drug for high blood pressure) to suppress painful memories in PTSD sufferers. There’s also a good article on this at the Smithsonian website.
The second area of research – more directly relevant to patients with FMS – is the recent use of Transcranial Magnetic Brain Stimulation or Transcranial Direct Current Stimulation (tDCS). Preliminary trials have been quite positive, although we cannot be certain how these low level and painless magnetic/electric fields can alter what is going on in the brain. One of the more plausible theories is that they may alter the neuronal excitation and thereby alter the abnormal levels of ‘amplification’ of signals in FMS. Is it possible that this works in a similar way to the memory modification techniques – splitting unhealthy links between sensory areas in the brain cortex from emotion/fear areas?
Some work that suggests a possible link was recently featured in a BBC Horizon programme on memory. In the programme a musician with ‘focal dystonia’ played the piece of music that he most associated with his early memories of the ‘twitch’ that had ruined his performing career. By recalling the memory whilst applying a low voltage current using tDCS the researchers felt that they could alter the excitation state of the neurons and dampen down the effect of the old memories. Old associations could potentially be ‘over-written’ by remembering a new performance with a more positive outcome.
If this early work with tDCS or Transcranial magnetic stimulation in FMS is replicated by independent researchers it will open up a whole new field of treatment. Our best proven interventions for treating FMS currently involve re-training the mind and body using graduated exercise programs or cognitive behavioral therapy. However, this is tough and some patients just can’t break out of the vicious cycle of pain, fatigue and insomnia.