Abstract
The response characteristics of olfactory receptor neurons (ORNs) and their corollary, the differential sensitivity and the resolving power, are fundamental to understand olfactory coding and the information extracted from a fluctuating olfactory signal. Previous work has focused on the temporal resolution of odor pulses presented for very brief periods at varying concentrations. The time course of the odor pulses as a stimulus parameter has not been considered. The present study investigated the precision of the ON and OFF ORNs on the antennae of the cockroach to discriminate increments and decrements of continuously rising and falling odor concentrations. Stimulation consisted of ramp-like upward and downward concentration changes in a trapezoid fashion. By varying ramp steepness, we examined the effect of the rate of concentration change. Both ORNs were clearly dependent on continuously rising and falling odor concentrations. As the rate of upward and downward concentration changes increases, differential sensitivity improves. Since the scatter of responses around the stimulus-response functions also increases, the resolving power for concentration increments and decrements deteriorates. Thus, the slower the rate of concentration change, the higher the precision in differentiating small concentration changes. Intuitively, the inverse relationship between the rate of concentration change and the resolving power is not surprising because accuracy requires time. A high degree of precision at slow concentration rates enables the cockroach to use information about the onset and offset slopes of odor pulses in addition to the pulse height to encode the spatial-temporal structure of turbulent odor plumes.
Highlights
Olfaction is generally thought to be a “slow” sense compared to “fast” senses such as vision and hearing (Laurent, 1999)
We describe here for the first time the ability of the cockroach’s ON and OFF olfactory receptor neurons (ORNs) to resolve increments and decrements of continuously rising and falling odor concentrations
The resolving power depends on the differential sensitivity, which is approximated by the slope of the stimulus-response functions, as well as on the reliability of the response, which is indicated by the scatter of individual points about these functions
Summary
Olfaction is generally thought to be a “slow” sense compared to “fast” senses such as vision and hearing (Laurent, 1999). Decades of research—using behavioral analysis and electrophysiological recordings—have led to the broad consensus that many insects and marine crustaceans tracking a turbulent odor plume are able to detect and respond to the intermittent pattern of the odor signal. There are several variations within this framework, almost all studies have focused on the speed or the rate of arrival of the odor signal as the key variable of the data. Nothing is known about the accuracy with which the concentration of the intermittent odor signal is determined. We address this question in the present study
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