- The seizure-generating area in the 'epileptic network' of the brain was considered to be the most important region of the brain for initiating seizures.
- Certain temporal and spatial changes within 'functional brain networks' with important nodes and links were investigated to gain better understanding of the seizure activity.
- The fluctuations of these individual nodes within functional brain networks can span from tens of seconds up to days, with strong contributions of daily rhythms, both related and unrelated to the disease.
Epilepsy is considered to be a 'network disease', which involves numerous connections within the brain. This epileptic network includes many areas of the brain involved in normal brain activity, during both seizure-free intervals and pathophysiological activities such as seizures.
A team of researchers from the University of Bonn are exploring the evolving 'epileptic brain networks' to further understand the brain activity in epilepsy patients and the role of different brain regions.
The mechanism of seizure is poorly understood though around 50 million people worldwide are affected by it. Around 25% of the seizures cannot be controlled by many treatments available today.
A research team from Germany is involved in constructing functional brain network using timed-based synchronization theory and space-based network theory.
Up until now, the most important region involved with seizure was considered to be the "seizure-generating area", in which the earliest signs of seizure activity can be observed. These findings were based on very limited data.
New Analytical Approach
Using the new analytical approach,the temporal and spatial variability of the importance of the brain's different regions were explored.
"New developments in network theory are providing powerful tools to construct so-called 'functional networks' from observations of brain activities such as the electroencephalogram (EEG), and helping to identify the important nodes and links within such networks," said Professor Klaus Lehnertz, head of the Neurophysics Group in the Department of Epileptology at the University of Bonn.
A link between a pair of nodes can be defined by assessing the degree of synchrony between neuronal signals from all pairs of nodes. The higher the degree of synchrony between the signals, the stronger the link.
"Applying these analysis concepts to multichannel long-term EEG recordings from 17 epilepsy patients with high temporal resolution allowed us to derive a sequence of functional brain networks spanning several days in duration," said Christian Geier, a doctoral student working with Lehnertz.
"For each network, we assess various aspects of the importance of individual brain regions with different centrality indices that were developed earlier for the social sciences. Then, we explore how the importance of network nodes fluctuates over time." Geier added.
The study reveals for the first time that the fluctuations of the individual nodes within functional brain networks can span from tens of seconds up to days.
Normal and daily rhythms of a patient contribute to a large part of these fluctuations and only a minimal part is attributed to phenomena directly related to the disease. "Rather, they take turns in importance on various time scales," Geier said. "And, depending on which aspect of importance is assessed, the seizure-generating area isn't -- as commonly believed -- the most important node within a large-scale epileptic network."
The understandings lay the foundation for developing treatments related to the causes and symptoms of epilepsy.
"When different brain regions assume the highest importance within a functional brain network is the key to improving both prediction and control of epileptic seizures," Lehnertz said. "In the long run, this improved understanding may enable the development of better treatment options for patients suffering from epilepsy. And understanding the importance of the nodes and links of functional brain networks may also be relevant for other neurological diseases."
The findings are published in Chaos.
- Epilepsy Fast Facts - (https://www.cdc.gov/epilepsy/basics/fast-facts.htm
- Klaus Lehnertz. Long-term viability of importance of brain regions in evolving epileptic brain networks. Chaos; (2017) doi: http://dx.doi.org/10.1063/1.4979796