Abstract
Despite a wealth of EEG epilepsy data that accumulated for over half a century, our ability to understand brain dynamics associated with epilepsy remains limited. Using EEG data from 15 controls and 9 left temporal lobe epilepsy (LTLE) patients, in this study we characterize how the dynamics of the healthy brain differ from the “dynamically balanced” state of the brain of epilepsy patients treated with anti-epileptic drugs in the context of resting state. We show that such differences can be observed in band power, synchronization and network measures, as well as deviations from the small world network (SWN) architecture of the healthy brain. The θ (4–7 Hz) and high α (10–13 Hz) bands showed the biggest deviations from healthy controls across various measures. In particular, patients demonstrated significantly higher power and synchronization than controls in the θ band, but lower synchronization and power in the high α band. Furthermore, differences between controls and patients in graph theory metrics revealed deviations from a SWN architecture. In the θ band epilepsy patients showed deviations toward an orderly network, while in the high α band they deviated toward a random network. These findings show that, despite the focal nature of LTLE, the epileptic brain differs in its global network characteristics from the healthy brain. To our knowledge, this is the only study to encompass power, connectivity and graph theory metrics to investigate the reorganization of resting state functional networks in LTLE patients.
Highlights
Brain dynamics arise from complex interactions that depend on several factors including neuron type [1,2,3], synaptic properties [2,3], gap junctions [4,5] and synchronization of neural oscillations [6,7,8]
While it is well known that the dynamics of the epileptic brain differ from the healthy brain during seizures and transition to seizures, we show that differences at multiple levels can be observed during the ‘‘dynamically balanced’’ state at rest with no task demand
left temporal lobe epilepsy (LTLE) patients were recruited from individuals who were determined to be candidates for resection surgery at Toronto Western Hospital and as such had focal seizures originating from the left medial temporal lobe that were refractory to medication
Summary
Brain dynamics arise from complex interactions that depend on several factors including neuron type [1,2,3], synaptic properties [2,3], gap junctions [4,5] and synchronization of neural oscillations [6,7,8]. A delicate balance between these factors gives rise to a stable dynamical state [9] that characterizes the healthy brain. This stable dynamical state is characterized by a balance between excitation and inhibition [10]. Epilepsy is of particular interest in understanding brain dynamics in general as the dynamical balance is only breached during a small time period over which a seizure occurs. This points to two important aspects that can shed some light on the functional impairment associated with epilepsy. How do the dynamics of the healthy brain differ from the ‘‘dynamically balanced’’ state of the epileptic brain; and, secondly, how does the transition occur between this ‘‘dynamically balanced’’ state to an epileptic state [13,14,15,16,17,18,19,20]? In this paper we pursue the first of these questions in the context of resting state dynamics
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