Michinori Ichikawa*, Gen Matsumoto**, Kazuyuki Aihara*** and Akira Tasaki*
*The University of Tsukuba
**The Electrotechnical laboratory
***The Tokyo Denki University
Abstract. The transition from the resting state of the squid giant axon to the state of spontaneous repetitive firing occurs when the sodium concentrarion of the external medium surrounding the squid giant axon is enhanced. The firing state can be regarded as a typical dissipative structure with an orbitally stable limit-cycle In the far-from-equilibrium system. Here we report periodic and non-periodic responses in squid giant axons to sinusoidal current stimulation duringspontaneous repetitive firing. The periodic or non-periodic trains of action potentials are analyzed with stroboscopic plots and Lorenz plots. The oscillations exhibited by the axon during sinusoidal current stimulation are classified into four cases: (1)entrained oacillations, (2)1/N entrained oscillations, (3)quasi-periodic oscillations and (4)chaotic oscillations.