A NONRANDOM DYNAMIC COMPONENT IN THE SYNAPTIC NOISE OF A CENTRAL NEURON

Continuous segments of synaptic noise were recorded in vivo from teleo st Mauthner cells and were studied with the methods of nonlinear analy sis, As in many central neurons, this ongoing activity is dominated by consecutive inhibitory postsynaptic potentials, Recurrence plots and first or third order Poincare maps combined with surrogate shuffling r evealed nonrandom patterns consistent with the notion that synaptic no ise is a continuously varying mixture of periodic and chaotic phases, Chaos was further demonstrated by the occurrence of unstable periodic orbits. The nonrandom component of the noise is reproducibly and persi stently reduced when the level of background sound, a natural stimulus for networks efferent to the Mauthner cell, is briefly elevated, Thes e data are consistent with a model involving a reciprocally connected inhibitory network, presynaptic to the Mauthner cell and its intrinsic properties, The presence of chaos in the inhibitory synaptic noise th at regulates the excitability of the Mauthner cell and its sensitivity to external stimuli suggests that it modulates this neuron's function , namely to trigger a fast escape motor reaction following unexpected sensory information.