This week, NTU Psychology senior lecturer Louise O’Hare gives us an overview of her recent review article, which was selected as the featured cover article of Vision, a peer-reviewed journal specialising in human and biological visual systems.
Migraine is the most common neurological disorder and is much more than just a headache – it can be very debilitating, resulting in many days off work or school each year. As well as the headache, there tend to be sensory symptoms during the attack, such as aversion to light and sound, nausea and vomiting.
Some people with migraine experience “aura”, a set of hallucinations preceding (around ½ hour) the onset of the headache. These hallucinations can take many forms, but a common one is a shimmering zig-zag pattern that expands with time.
These hallucinations are thought to be caused by a wave of neural activity, called cortical spreading depolarisation. You can think of this a bit like a tsunami, lots of activity, and then all quiet afterward. This spreading depolarisation expands over the cortex at the same rate as the hallucinations appear, which leads us to think they are linked.
Mathematicians have created models (sets of mathematical equations that predict complex behaviour), originally based on the work of Turing, to understand this cortical spreading depolarisation and how this brain activity might result in the hallucinations typical of migraine. These models could potentially give valuable information about how migraine attacks start. However, it is not currently possible to directly measure cortical spreading depolarisation in people with migraine, and so it’s not possible to test them directly.
These mathematical models are theoretical predictions, and so it is important to know if they are right. To do this, we would need to see if the model can predict experimental data. There have been some electrophysiological recordings of overall brain activity in people with migraine attacks, but this is very sparse, as people tend not to have attacks conveniently in the laboratory. Although there are lots of anecdotal reports, there is little information from scientific studies about what people report as their triggers of migraine. Some examples include flickering lights, stress and sleep deprivation, and these are important as we know something about how these might affect the brain (although this is also complicated). There are also indirect measures by asking people with migraine to do visual tasks and seeing what is different in their performance compared to control groups. We can also plan some experiments to test the theories of the models, even though these will have to be indirect.
Then, if these models are right, we will be able to use them to understand more about what elicits the migraine attack. There are several therapies to treat the symptoms of an attack that has already started (e.g. painkillers), or to lower the risk of attacks (“prophylactic treatment”). However, these aren’t suitable for everyone, or don’t always work. It may be better to understand what causes the attack and try to prevent this from happening. These models might be the key to doing this and that is why this kind of work is so important.
The conclusions of the review article open up more questions than are actually answered, as migraine aura is still poorly understood. This only emphasises the need for more research and potential opportunities for budding researchers with an interest in this area. For example, what links the migraine aura to the pain of the headache, is there any possibility of long-term damage from repeated migraine attacks, and why are there sex differences in migraine? Understanding more about the migraine aura could well start with these sophisticated mathematical models, to give some concrete directions about what we need to investigate to understand the onset of the attacks.
You can read the full article here: O’Hare, L., Asher, J. M., & Hibbard, P. B. (2021). Migraine Visual Aura and Cortical Spreading Depression—Linking Mathematical Models to Empirical Evidence. Vision, 5(2), 30. MDPI AG. Retrieved from http://dx.doi.org/10.3390/vision5020030
Dr. Louise O’Hare
Louise’s research focuses on individual differences in visual perception, using both behavioural and electrophysiological methods. It involves investigating individual differences in visual perception, in particular visual discomfort. As well as her migraine-related research, Louise’s work has also investigated experiences when using virtual reality displays.
Psychology at Nottingham Trent University 