Directional and frequency characteristics of auditory neurons in Culex male mosquitoes

The paired auditory organ of the mosquito, the Johnston's organ (JO), being the receiver of the particle velocity component of sound, is directional by its structure. However, to date almost no physiological measurements of its directionality have been made. In addition, the recent finding on the grouping of the JO auditory neurons into antiphase pairs demands 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 relationships in physiologically distinguishable groups - pairs or triplets. The feedback stimulation method allowed us to discriminate responses of the two simultaneously recorded units, and to show that they indeed responded in antiphase. Units of different frequency tuning as well as highly sensitive units (thresholds of 27 dB SPVL and below) were found in every angular sector of the JO, providing the mosquito with the ability to produce complex auditory behaviors.