Directional and frequency characteristics of auditory neurons in Culex male mosquitoes

The paired auditory organ of mosquito, the Johnston’s organ (JO), being the receiver of particle velocity component of sound, is directional by its structure. However, to date almost no direct physiological measurements of its directionality was done. In addition, the recent finding on the grouping of the JO auditory neurons into the antiphase pairs demanded confirmation by different methods. Using the vector superposition of the signals produced by two orthogonally oriented speakers, we measured the directional characteristics of individual units as well as their relations in physiologically distinguishable groups – pairs or triplets. The feedback stimulation method allowed to discriminate responses of the two simultaneously recorded units, and to show that they indeed responded in antiphase. We also show that ratios between the individual tuning frequencies in pairs and triplets are non-random and follow the principle of harmonic synchronization, remarkably similar to the one known from the observations of mosquito behavior. Units of different tuning and sensitivity are evenly distributed around the axis of the JO, providing the mosquito with the ability to produce complex auditory behaviors. Summary statement Auditory neurons of mosquito are grouped into pairs or triplets, each unit tuned to a specific frequency. Within the pair units respond to opposite directions of the sound. Units of different tuning and sensitivity are evenly distributed around the axis of the Johnston’s organ.