Abstracts

RATIONALE: The neuronal mechanisms responsible for interictal epileptiform discharges are not well understood. Recently model networks of integrate-and-fire (IF0) neurons have been shown to exhibit self-organized criticality (SOC) (1, 2), which describes the behavior of complex dynamical systems that evolve to a critical state from which large energy fluctuations can occur.
METHODS: We analyzed data from seven consecutive patients with mesial temporal lobe epilepsy who required monitoring with temporal lobe depth electrodes during evaluation for epilepsy surgery. The patients had six-contact depth electrodes placed stereotaxically within each mesial temporal lobe. All intracranial electroencephalogram recordings (iEEG) were visually reviewed by an epileptologist to identify the seizure onset zone. Continuous iEEG were collected using a digital, 64 channel, 12-bit Nicolet BMS-5000 epilepsy monitoring system. The referentially recorded iEEG was digitized with a 200 Hz sampling rate and band pass filter of 0.1-100 Hz. The probability densities of interictal energy fluctuations within the seizure onset zone were determined.
RESULTS: For the seven patients evaluated the probability densities of anomalous large energy fluctuations in the ictal onset zone on interictal iEEG were found to scale as (energy)^-[delta], and the quiescent time between epileptiform energy fluctuations scaled as ([delta]t)^-[gamma]. Here [delta] and [gamma] are patient specific scaling constants that are determined by fitting the experimental data. The scaling relations were not found outside the ictal onset zone.
CONCLUSIONS: We demonstrate the primary features of SOC in the iEEG of seven patients with temporal lobe epilepsy. These findings in human temporal lobe epilepsy provide new insight into possible mechanisms underlying interictal epileptiform discharges and provide a connection to (IFO) network models. The results may also have utility in understanding the network mechanisms involved in seizure generation, and provide insight about how local electrical stimulation can prevent seizures.
References:
1.A. V. Herz, Hopfield, J.J., Physical Review Letters 75, 1222-1225 (1995).
2.J. J. Hopfield, Herz, A.V., Proc. Natl. Acad. Sci. 92, 6655-6662 (1995).
[Supported by: Acknowledgements: Dr. Worrell is funded by a Mayo Foundation Scholar grant from the Mayo Clinic Foundation. Dr. Cranstoun is funded by a National Science Foundation Graduate Research Fellowship and NIH grant # T32-GM07517. Dr. Litt[ssquote]s research is funded by The Whitaker Foundation, The American Epilepsy Society, The Dana Foundation and National Institutes of Health Grants# RO1NS041811-01 and MH-62298RO1]