Network Propagation in Epileptic Seizures
Abstract number :
2.061
Submission category :
Year :
2001
Submission ID :
677
Source :
www.aesnet.org
Presentation date :
12/1/2001 12:00:00 AM
Published date :
Dec 1, 2001, 06:00 AM
Authors :
H. Bahcivan, M.Sc., Biomedical Engineering, Johns Hopkins University, Baltimore, MD; N. Zhang, MD, Biomedical Engineering, Johns Hopkins University, Baltimore, MD; M.A.Z. Mirski, MD, Ph.D., Anesthesiology and Critical Care Medicine, Johns Hopkins Universi
RATIONALE: Our investigation of the large-scale network mechanisms of epilepsy focuses on the cortical and subcortical field recordings in order to support the existence of a thalamo-cortical propagation pathway during the seizure discharge activity. Previous work showed that field potentials originated in anterior thalamus and propagated with non-zero time delay to cortex. We wish to extend this finding to another member of the limbic circuit of Papez, or the hippocampus and calculate stability of systemic delays.
METHODS: Field recordings have been obtained from cortex (CTX), anterior thalamic nuclei (AN), posterior thalamus (PT), an unaffiliated nucleus and hippocampus (HPC) during pentylenetetrazol (PTZ) seizures in anesthetized (halothane, 0.5%) animals (N=5). Cortical screw electrodes (frontal-2 mm A to bregma) and twisted pair electrodes for subcortical sites recorded signals sampled at 1000 Hz. Cross-correlation analysis of the field recordings is a potential approach to estimate the strength of linkage or pathway between two neural circuits. Wavelet Transform Cross Correlation (WTCC) is a novel method to estimate delays of wideband signals such as our subcortical recordings. We have constructed delay histograms at different ranges of frequencies/scales. Using basic entropy measurements, the dispersion of the histograms was quantified and we obtained an indicator of the volatility level of the delays for different neuronal elements.
RESULTS: Our results from delay histograms for particular bands reveal stable propagation delays mostly at the HPC-AN-CTX axis with multiple delay peaks located at +20-70ms for each of the two subpaths of the circuit. We have calculated the entropy of the delay histograms with 100 bins @4ms/bin as a measure of the histogram dispersion. Partial path delay histogram entropies from HPC-to-AN and AN-to-CTX reveal the means of 3.57 and 3.64 (s.d. 0.50,0.63) at the scale range 8-31Hz, respectively. The delay histograms for the seizure pathways involving PT are widely distributed with histograms having a mean entropy of 4.37 (s.d., 0.57) within the same scale range.
CONCLUSIONS: Our positive definite delays reaffirm the fact that there is a definitive subcortical origin to the ictal discharge. Additional evidence amounts to the fact that hippocampus has direct input to anterior thalamus. Hippocampus to AN directionality is confirmed in our analysis. The behavior observed in the brain recordings analyzed in this paper allows us to make the claim that discharges are generated in a serial process by spatially distinct neuronal circuits. The fact that significant differences in delay histogram entropy exists across channels suggests that there is selectivity in network involvement for each channel in ictal propagation.
Support: NINDS35528.