Abstracts

RATIONALE: Our previous studies disclosed the excitability change of the brainstem which precedes synchronized activities in the cortex: 3-Hz spike-and-wave complex (Brain Res. 1999; 837: 277-288); spindle oscillation (Brain Res. 2000; 882: 103-111) and poly spike-and-wave complex (Brain Res. 2001; in press). The investigation was carried out by simultaneous analyses of brainstem auditory evoked potentials (BAEPs) with EEGs. The method was based on the characteristics of BAEPs, ie. [ssquote]far-field evoked potentials[ssquote]. Here, we investigated the functional change of the brainstem before and during the epileptic discharge, recruiting rhythm (RR), by the same analysis.
METHODS: Six patients with epilepsy (2 males, 4 females; aged from 7 to 15 years; 4 primary generalized epilepsies, 2 frontal lobe epilepsies) were selected for this investigation. i) Six-channel EEGs (including Cz-A1, Cz-A2 for BAEPs) and an acoustic trigger signal (80-dB binaurally applied clicks with 20/s repetition rate) were recorded and sampled (10-kHz sampling frequency). ii) Four to ten sequences of RR were selected. The onset of RR was located with 16 segments (one segment, 512-point EEG data containing one trigger signal) in each sequence of RR. BAEPs were averaged in these 64 to 160 segments ([ssquote]onset[ssquote]). iii) As the averaging area was shifted by 2 segments backward, BAEPs were calculated in each shift ([ssquote]B1[ssquote], [ssquote]B2[ssquote], ...[ssquote]B26[ssquote]). Then, BAEPs were calculated in each forward shift of the averaging area ([ssquote]A1[ssquote], [ssquote]A2[ssquote], ...[ssquote]A16[ssquote]).
In forty-two arrays of BAEPs, the excitability change of the ventral brainstem was measured as wave-III amplitude and area, and the excitability change of the dorsal brainstem was measured as wave-V amplitude and area. Following normalization, these four parameters were tested for a time course difference among the patients by one-way repeated measures of ANOVA.
RESULTS: The excitability change of both ventral and dorsal brainstem showed the same time course development: two parameters (amplitude and area) increased from [ssquote]B20[ssquote] (-2.4 +/- 0.4s) attaining the maximum at [ssquote]B4[ssquote] (-0.8 +/- 0.4s), then rapidly decreased in both wave-III and wave-V; and the emergence of RR in EEGs corresponded to the period of decrement.
CONCLUSIONS: Experimental studies have disclosed a sustained depolarization preceding the rhythmic bursts in-vitro cortices. Although the sustained depolarization in the cortex is considered to depend on the excitatory transmission, its triggering mechanism remains unsolved. The present result suggests that, in human epilepsy, the RR is triggered by the widespread transient brainstem activation. And, this activating pattern differs from that of spindle oscillation.