CORTICAL SYNCHRONIZED ACTIVITY EVOKED BY THALAMOCORTICAL STIMULATION IN-VITRO

Epileptiform activity was studied in the thalamocortical (THC) slice p reparation. Inhibition was gradually attenuated with increasing doses of bicuculline methiodide (BMI). We compared the ability of thalamic a nd intracortical (INC) stimulation to evoke epileptiform activity. Syn chronized population activity was identified by its all-or-none appear ance at a threshold stimulus intensity, by a variable latency and by h orizontal propagation to large distances. For most slices (20 out of 2 4) we could establish a threshold dose of BMI (0.4-0.7 mu M) under whi ch THC-evoked population events had epileptiform properties, while INC -evoked ones did not. Increasing the BMI dose by 0.2 mu M resulted in the appearance of epileptiform field potentials when stimulating intra cortically. It is concluded that the tendency of the neocortex to gene rate synchronized population activity is higher when it is activated t hrough the THC pathway.