Abstracts

Following severe head trauma, 10 - 50% of survivors will develop epilepsy. Identifying the subset of individuals that will go on to have chronic seizures would greatly improve their clinical care. We used the repeated low-dose kainate model of temporal lobe epilepsy to investigate the spectral content of the EEG before and after treatment (pre-ictal) to determine if there are EEG predictors of future epilepsy., We used implantable radiotelemetry units to continuously monitor the EEG in freely behaving rats. Three sets of rats were observed: (1) rats treated until motor status (MSE) (n = 5), (2) rats treated until electrical status (ESE) (n=5), and (3) saline treated rats (n=3).
An average Fast Fourier Transform was calculated using the Welch method and a rectangular window. Each window contained 65,536 points (262 sec). The results were averaged over an entire day (329 windows). Three power sectra were compared: (1) prior to kainate, (2) 3 days after kainate, and (3) 8 days after kainate., All MSE rats developed chronic epilepsy. Their power spectrum did change after kainate administration. In 4/5 of the rats considered, the total power increased. The increases corresponded mostly to the lower frequencies, below 5 Hz. These increases persisted in 3/5 of the rats 8 days after treatment. By comparing the spectral density when frequent spikes are present (this was present only with MSE rats) with that when they were absent, we note that there is an increase in both high frequency (due to the sharpness of the spike) and low frequency (due to the periodicity of the spiking) power. We note that the results were invariant to the type of window used (Hamming, Hann, rectangular).
None of the ESE rats developed chronic seizures. In these rats, we note that the total power decreased after kainate treatment in 4/5 of the rats. The fact that the power does not increase is not surprising because visually there was no change in the signal (no spikes). We also do not see the low frequency increase in the power spectrum noted in the MSE rats.
For control rats the average EEG total power changed by only 10% from before to after kainate treatment., Kainate-injured rats that develop epilepsy exhibit spectral changes (increases in low-frequency power) in the EEG that appear prior to the onset of frequent motor seizures. Some of these spectral changes are due to the appearance of spikes (either individually or in clusters). If similar changes are found to be present in humans, it could be possible to predict whether an individual is likely to go on to develop chronic epilepsy following a brain injury. This will have a large positive influence on the care of patients with brain injury and could focus treatment trials on those at highest risk., (Supported by Funding was provided by the NIH.)