Comment on "Dynamics of some neural network models with delay".
Based upon numerical evidence, Ruan et al. [J. Ruan, L. Li, and W. Lin, Phys. Rev. E 63, 051906 (2001)] suggest that the delay differential equation dx/dt(t)=-x(t)+A tanh[x(t)]+B tanh[x(t-tau)] may display chaotic dynamics. As mentioned by Pakdaman and Malta [IEEE Trans. Neural Netw. 9, 231 (1998)], this equation presents a monotonic delayed feedback, so that it satisfies a Poincaré-Bendixson-like theorem, ruling out the existence of complex aperiodic dynamics.
Pakdaman
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Inserm U444, Faculté de Médecine Saint-Antoine, 27, rue Chaligny 75571, Paris Cedex 12, France.
Malta
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