Response of the Medial Octavolateral Nucleus (MON) in the Goldfish, <i>Carassius auratus</i>, to constant-amplitude and amplitude-modulated water wave stimuli

Abstract

<p>Lateral line units in the MON of goldfish exhibited phasic or tonic responses to constant-amplitude stimuli. When stimulated with amplitude-modulated stimuli, most MON units exhibited phasic-tonic or tonic responses that were phase-locked to the modulation frequency. On average, phase-locking to the modulation frequency was greater than phase-locking to the carrier frequency. Thus, MON responses to amplitude-modulated sine wave stimuli differed from those of afferent fibres in the posterior lateral line nerve (strong phase-coupling to both carrier and modulation frequency) and were similar to those of midbrain lateral line units (strong phase-coupling only to the modulation frequency).<br /> When modulation depth was maximal (96%), units responded to each modulation cycle with about the same number of spikes. When modulation depth was less than maximal, units tended to discharge with a decreasing number of spikes to increasing numbers of AM cycles. When modulation depth was 24% or smaller, discharge patterns resembled the responses to unmodulated CFs, i.e. units responded with an on-response to the first AM cycle but responded only weakly to successive AM cycles.<br /> Lateral line units in the MON of goldfish increased their discharge rates and the degree of phase-locking with increasing displacement amplitudes of the vibrating sphere.<br /> Most level response functions were steep, i.e., discharge rates increased over a narrow range of displacements (50 μm to 175 μm).<br /> Goldfish medullary lateral line units encode a wide range of stimulus displacements. </p>