Chaotic responses of the hippocampal CA3 region to a mossy fiber stimulation in vitro.
Undoubted evidence of chaotic activity of a biological neural network are given. Spontaneous epileptiform bursts of a neuron population in the CA3 region of rat hippocampal slices were caused in a perfusing medium with 2 mM penicillin and 8 mM K+ ions, and responses of field potential in the CA3 region to a periodic mossy fiber stimulation were investigated. Phase-locked and chaotic responses occur depending on stimulus parameters; for example, when the frequency of the stimulation increases, 1:1 phase-locking bifurcates to chaos through 1:2 phase-locking. The chaotic responses show a broad-band spectrum, and their trajectories in the three-dimensional phase space (V(t), V(t + tau), V(t + 2 tau)) reconstruct a strange attractor. Lyapunov exponents of the strange attractors estimated by the Wolf's algorithm are positive. Moreover, one-dimensional strobomaps obtained from the chaotic responses show a non-invertible function. Since the slope of each strobomap at their fixed point is more negative than -1, the fixed points are unstable. These are undoubted evidences for chaotic responses of the CA3 region in hippocampal slices maintained in vitro. Cross-correlation functions between field potential responses which were simultaneously observed at different sites show that the responses are spatially coherent throughout the CA3 region even when the responses are chaotic.
Hayashi
H
H
Department of Computer Science and Electronics, Kyushu Institute of Technology, Iizuka, Japan.
Ishizuka
S
S
D000200:Action Potentials; D000818:Animals; D004558:Electric Stimulation; D004827:Epilepsy / Q000473:pathology / Q000503:physiopathology; D006624:Hippocampus / Q000187:drug effects / Q000473:pathology / Q000503:physiopathology*; D066298:In Vitro Techniques; D008297:Male; D009412:Nerve Fibers / Q000502:physiology; D009474:Neurons / Q000502:physiology; D010406:Penicillins / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
D010406:Penicillins; D011188:Potassium