Rat thalamocortical slices maintain synoptic connections between thalamus and cortex. When perfused with low Mg++-ACSF, thalamocortical slices exhibited two main types of spontaneous bursting activity. One is monotonic burst of 3-15 Hz and another is multiphasic bursts which have a tonic burst firing period and a late phase of clonic burst firing. These bursts are similar in frequency and during to EEG recordings from human generalized seizures. Exploiting the advantages of in vitro preparations, the electrophysiological action of taurine were studied. Exogeneous application of taurine profoundly decreased spontaneous bursting activities, which it caused only slight reduction of electrically evoked response in cortical layer. Taurine-induced current was blocked by 40 uM bicuculline, GABA receptor antagonist, in acutely isolated coritcal neurons. These results suggest that endogeneous taurine may regulate the hyperexcitablility through GABAa receptor.