Photosensitivity and epilepsy: Current concepts and perspectives – A narrative review
Introduction from Dr Markus Reuber, editor-in-chief of Seizure
Many species have one predominant sense. For dogs, it’s the sense of smell for cats and humans it is vision. To those who want to be amazed about just how dominant vision is in humans over their other senses (or those who want to find out more about how perception works in general) I recommend searching YouTube for the McGurk effect and carrying out a self-experiment. What you will learn is that what we hear (in this case “bah” or “fah”) is not determined as much by the sound presented but by how we interpret the movements of the speaker’s lips. When we see “bah” this is what we hear, even if the actual sound is “fah”.
Given this predominance of vision over our other senses, it is perhaps no surprise that visually presented stimuli are the most common triggers of provoked epileptic activity and epileptic seizures. Perhaps it is the same reason that prompted researchers to use photic stimulation very soon after the initial description of the application of electroencephalographic (EEG) method in humans to evaluate its effects on the EEG and to deliver the initial account of photosensitivity in 1934 (1).
My editor’s choice from the current issue of Seizure by A Martins da Silva and Bárbara Leal provides a narrative review of our development of the significance of photosensitivity and abnormal responses to intermittent photic stimulation since this discovery (2). This additional contribution to the 25th Anniversary of Seizure is a masterly and comprehensive account of everything you ever needed to know about a phenomenon observed in as many as 5% of people with epilepsy. We learn that photosensitive epilepsy (PSE) is commoner in younger individuals, more frequent in women, often time-limited, generally easy to treat and closely related to generalised epilepsies. Structural and functional studies of PSE indicate abnormalities beyond the frontal lobes and, not surprisingly, provide evidence for the role of the visual cortex in human PSE. Photoparoxysmal responses are interpreted as a final expression of pathogenic phenomena in the striato-thalamocortical system. The familial transmission of epileptiform responses to IPS is well-recognised, but no clear relation between PSE and specific genes has emerged.
(1) Adrian ED, Matthews BH. The Berger rhythm: potential changes from the occipital lobes in man. Brain. 1934;57:355 – 85.
(2) Da Silva AM, Leal B. Photosensitivity and epilepsy: current concepts and perspectives, a narrative review. Seizure 2017; 50: 209-218.