Hamandi, K, Singh, K and Muthukumaraswamy, S (2010-2012) Magnetoencephalographic measures of abnormal sensory oscillations: a new window on photosensitive epilepsy. Epilepsy Research UK. £99,980 (Cardiff Funding: £99,980)
Magnetoencephalography (MEG) of induced visual cortex responses can provide a window on theabnormal activity underlying photosensitive epilepsy(PS). Healthy volunteer MEG studies have demonstrated that specific visual stimulus parameters are encoded in gamma frequency responses.Individual variability in these measures have recently been shown to correlate with age and magnetic resonance spectroscopy measures of inhibitory neurotransmitter(GABA)concentration. Low-level visual stimuli can be used to elicit these MEG responses and hence have low risk of provoking seizures.Our early pilot data in juvenile myoclonic epilepsy show novel findings in these gamma responses with strikingly low gamma peak frequency in some and altered spectral properties. We aim to extend this work with a systematic study in patients with PS. We hypothesize that patients with PS will have lower induced gamma frequencies compared to controls and a greater increase in stimulus-motion associated frequency shifts. In addition, we will explore the spread and longer-range effects of evoked and induced responses and the relationship of response characteristics to other stimulus variations. As well as furthering the understanding of PS this work has the potential to improve diagnostic investigation in epilepsy and develop tools to assess drug responsiveness, and drug development and discovery.
It is well known that flashing lights can bring on seizures in certain types of epilepsy. Precisely why this happens remains unclear but it seems to be related to nerve cells firing together in abnormal ways. Abnormal nerve cell firing or synchronisation plays a key role in all epileptic seizures, and this is seen as abnormal frequency oscillations before or during seizures. A technique known as magnetoencephalography (MEG) measures tiny magnetic field changes at the scalp surface due to underlying neural activity, and is comparable to the way the electroencephalogram (EEG), a standard investigation in epilepsy, measures electrical changes at the surface. An advantage with MEG is a superior ability to measure and localise neuronal oscillations. The technique is non-invasive, i.e. it doesn’t involve radiation, needles or surgical procedures, and can be used to compare measures in healthy subjects and patients with epilepsy. By studying the brain’s responses to simple visual patterns, in patients with and without photosensitive epilepsy and comparing with healthy controls, we hope to start to unravel novel aspects and measures of neuronal function that influence the abnormal synchronisations seen in epilepsy. We expect the results will be applicable to patients in the medium term (3-5 years).