Submitted on December 8, 2006
Accepted on September 10, 2007
Noise - Induced Transition to Bursting in Responses
of Paddlefish Electroreceptor Afferents
Alexander B. Neiman1*, Tatyana A. Yakusheva2, and David F. Russell3
1 Physics and Astronomy, Ohio University, Athens, Ohio, United States
2 Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri, United States
3 Biological Sciences, Ohio University, Athens, Ohio, United States
* To whom correspondence should be addressed. E-mail: neimana{at}ohio.edu.
Response properties of ampullary electroreceptors of paddlefish were studied in vivo, as single-unit afferent responses to external electrical stimulation with varied intensities of several types of noise waveforms. (i) Weak noise increased the variability of afferent firing, but it remained tonic. (ii) In contrast, stimulation with less-weak broadband noise led to a qualitative change of the firing patterns, to parabolic bursting, even though mean firing rates were little-affected. (iii) The transition to bursting was marked by the development of two well separated time scales: the fast frequency of spiking inside bursts at up to 250 spikes/s, and the slow frequency of burst occurrences at ~9 bursts/s. These two time scales were manifested as two regimes of afferent power spectra, and bimodal interspike interval histograms, return maps and autocorrelations. (iv) The stochastic ~9 Hz bursts were not simply driven by similar-frequency components of noise stimuli, since bursts could be dissociated from stimulus waveforms using high-pass filtered noise, or a 0.1 Hz sine wave stimulus. (v) Arrhenius plots showed that the threshold noise intensity required to elicit bursting depended on the frequency content of a noise stimulus, being lowest, ~1.2 µV/cm, for stimuli matching the 120 Hz best response band of these cathodally excited ampullary electroreceptors. (vi) Comparable threshold values for bursting came from an alternate analytical approach that we developed, based on correlation times of spike trains. (vii) Simultaneous recordings from pairs of afferents showed that their bursting frequencies (bursts/s) always converged as the amplitude of a noise stimulus was raised.
