Epileptic activity found to spread in a new way

Scientists have identified a new way in which epileptic activity is able to spread through the brain. Researchers from the biomedical engineering department at Case Western Reserve University, US, have found that individual cells are able to stimulate epileptic activity in neighbouring areas of the brain - allowing it to spread. It is thought that the latest discovery could lead to the development of new seizure-blocking treatments.

A series of experiments presented evidence that suggests cells within the hippocampus stimulate and synchronize activity in neighbouring cells via an electrical field, which serves to allow epileptic activity to spread through each cell layer. This mechanism for cell interaction has never been identified before and allows for a wave of activity to be created.

Published in the 'Journal of Neuroscience', the study involved the insertion of a 64-channel microelectrode array into a mouse model's unfolded hippocampus. This array allowed the researchers to monitor activity throughout that area of the brain. The hippocampus was then injected with a drug to make it epileptic.

By reducing the calcium ion concentration level to below that which is usually involved in signalling, the researchers were able to block signals from being transmitted via the chemical synapses. They then injected the antimalarial drug mefloquine, which stopped signals from being electronically transmitted across synapses. It was found that epileptic activity still spread at around 0.1 meter per second, even without synaptic transmission.

The speed at which it was able to spread ruled out the third possible route for propagation of epileptic activity. This involves the diffusion of potassium and sodium ions creating the signal and is much slower than the speed at which activity spread in the experiment. 

Only one other way of neuron communication could explain the speed at which activity was found to spread, electrical fields. This occurs when a group of cells fire together and result in electrical fields and currents that can result in further activity from neighbouring cells.

Researchers developed a computer model that showed a large set of neurons could spread the epileptic activity at the same speed as was shown in the experiment. The model also suggested that the signal transmission could alter in speed depending on the distance between the neurons.