Stochastic phase synchronization in the crayfish mechanoreceptor/photoreceptor system

The two light-sensitive neurons in the crayfish's abdominal sixth ganglion ("caudal photoreceptors," or CPRs), are both primary light sensors and secondary neurons in a mechanosensory pathway. Pei (1996) demonstrated that light enhances the transduction of weak, periodic hydrodynamic stimuli (measured as an increase in the signal-to-noise ratio at the stimulus frequency in the power spectrum of the recorded neural spikes). This has been interpreted as a stochastic resonance effect, in which added light increases the noise intensity of the input to the photoreceptor (possibly through fluctuations in membrane potential), leading to an enhancement of the signal-to-noise ratio (SNR). Here, we discuss the recent demonstration (Bahar , 2002) of the correlation between a stochastic-resonance-like effect and an increase in stochastic phase synchronization between the neural response and a periodic mechanical stimulus. We also discuss a novel effect (Bahar , 2002) in which light increases the SNR of the second higher harmonic of a periodic input signal, effectively rectifying the input signal. This "second harmonic effect" can also be interpreted in terms of stochastic phase synchronization (Bahar , 2002). We review other recent results on the role of stochastic phase synchronization in mediating sensory responses in the crayfish nervous system. (C) 2003 American Institute of Physics.