Abstract
The cercal sensory system of cricket mediates the detection, localization, and identification of air current signals generated by predators, mates, and competitors. This mechanosensory system has been used extensively for experimental and theoretical studies of sensory coding at the cellular and system levels. It is currently thought that sensory interneurons (INs) in the terminal abdominal ganglion extract information about the direction, velocity, and acceleration of the air currents in the animal's immediate environment and project a coarse-coded representation of those parameters to higher centers. All feature detection is thought to be carried out in higher ganglia by more complex, specialized circuits. We present results that force a substantial revision of current hypotheses. Using multiple extracellular recordings and a special sensory stimulation device, we demonstrate that four well-studied interneurons in this system respond with high sensitivity and selectivity to complex dynamic multidirectional features of air currents that have a spatial scale smaller than the physical dimensions of the cerci. The INs showed much greater sensitivity for these features than for unidirectional bulk-flow stimuli used in previous studies. Thus, in addition to participating in the ensemble encoding of bulk airflow stimulus characteristics, these interneurons are capable of operating as feature detectors for naturalistic stimuli. In this sense, these interneurons are encoding and transmitting information about different aspects of their stimulus environment; they are multiplexing information. Major aspects of the stimulus-response specificity of these interneurons can be understood from the dendritic anatomy and connectivity with the sensory afferent map.NEW & NOTEWORTHY A set of sensory interneurons that have been studied for over 30 years by several different research groups were discovered to have previously unknown encoding characteristics. As well as encoding the direction of bulk airflow with a coarse-coding scheme as shown in previous studies, these interneurons are also responsive to very small-scale, directionally complex air current waveforms. This feature sensitivity can be understood in terms of the cells' complex dendritic branching patterns.