Propagation of epileptiform activity during development of amygdala kindling in rats: linear and non-linear association between ipsi- and contralateral sites.

The relationship between ipsi- and contralateral epileptiform electroencephalographic (EEG) activity was investigated in rats that were kindled daily in the amygdala. Two types of relationships--linear and non-linear associations--were studied and used to estimate time delays of EEG activity between homotopic amygdalar sites during consecutive tetanizations. The progressive development of epileptiform EEG and convulsive behaviour was accompanied by an increase in association. Maximal association values of the non-linear function were significantly higher than linear association values. The gradual development of motor seizure severity was correlated with increased non-linearity. Time delays between the two amygdalae were estimated comparably with the linear and non-linear function: 30.0 +/- 3.3 and 24.6 +/- 1.7 ms (ipsilateral leading contralateral), respectively. However, in rats displaying exclusively bilaterally generalized motor convulsions, maximal values of both functions decreased but were still significantly higher than control values of phase-randomized EEG. Corresponding positive as well as negative interhemispheric time delays were recorded during the afterdischarge. These results demonstrated a strengthened association between the ipsi- and contralateral amygdala during primary epileptogenesis induced by amygdala kindling. In contrast, development of a secondary focus in the contralateral homotopic region resulted in a weakened interhemispheric association. Secondary bilateral synchrony between the ipsi- and contralateral amygdala occurred during the evoked epileptiform EEG activity.