In this study, using the double and sharp microelectrodes and patch clamp techniques, intracellular recordings were performed in the neurons of mice cochlear nucleus, rat inferior colliculus and subesophagial ganglia ol Helix aspersa in vitro. In these neurons, alter hyperpolarization potential (AHP) consisted ol fast (f-AHP), medium (m-AHP) and slow (s-AHP) phases. Occasionally, alter depolarization potential (ADP) was observed. The amplitude of the AHP varied depending upon the types of cells (could be as big as 25 mV). The possible role of the AHP was investigated by enjecting hyperpolarizing currents before depolarizing neurons. Consequently, it was observed thai preconditioning hyperpolarizing current caused the firing patterns of the neurons.