Extreme events occur in a wide variety of contexts. In general, they are considered to be rare events characterized by a large impact on a particular system which is measured in terms of very different quantities. In our work we study phenomena in excitable systems which appear recurrently in rather large, irregularly spaced time intervals. In particular, we focus on two such extreme events, namely the recurrent occurrence of harmful algal blooms in the ocean and the recurrent emergence of epileptic seizures in the human brain.
Harmful algal bloom appear when a toxic species of algae (e.g. dinoflagellates or cyanobacteria) becomes extremely abundant and dominant in a plankton community. The emergence of such blooms can not only be dangerous for direct competitors or consumers of the toxic algae, but also for higher organisms such as shellfish, fish, birds and mammals as well as for human beings, either by direct toxin effects or indirectly by propagating effects up the food web (e.g. algal toxins accumulate in fish or shellfish that are consumed). Therefore, these blooms can have dramatic effects on human health and industry.
Epileptic seizures are a clinical manifestation of an excessive and hyper-in rhythm activity of neurons in the brain. Epilepsy affects approximately 1% of the world’s population, and in about 25% of individuals with epilepsy, seizures cannot be controlled by any available therapy. Epileptic seizures might be considered less extreme mainly due to the limited public awareness, but doubtlessly they are extreme for those affected. The recurrent and in the majority of cases sudden incidence of epileptic seizures as well as disturbance of consciousness and sudden loss of motor control can lead to dangerous and possibly life-threatening situations. Thus, if it were possible to forecast epileptic seizures, therapeutic possibilities would change dramatically. Our aim is to study these phenomena in some detail and also to explore the similarities between them.