Meeting Abstract
P3.103 Wednesday, Jan. 6 CNS processing of auditory signals differs in light and darkness in the praying mantis, Parasphendale agrionina SIMPSON, M. C.; YAGER, D. D.*; Univ. of Maryland, College Park; Univ. of Maryland, College Park ddyager@umd.edu
Most praying mantises detect ultrasound using a single ear in the ventral midline of the metathorax. This provides early warning of a bat attack and triggers an effective evasive response. The head is necessary for the behavioral response, but descending control has not previously been studied. Ascending auditory information in 3-5 axons reaches the head 13-15 ms post-stimulus. Extracellular recording from the lateral half of the descending connective typically shows an early response of several units (latency 22-35 ms) followed at >100 ms post- stimulus by activity in 3-4 very large units that can extend several hundred ms after the 200 ms stimulus train. The overall spike numbers for the descending responses when the animal was in darkness compared to when it was in light averaged 45% greater (range 18%-81%), but response duration was the same. The darkness responses immediately after lights off typically had fewer spikes than after 10 min. in the dark. Although descending responses under both conditions can be variable, habituation of responses in darkness was slower than in light in some experiments. Experiments were carried out during the animalsʼ subjective day, which makes the greater darkness responses especially surprising. We predict that physiological experiments during dusk and the first half of the animalsʼ night, the peak activity period for this species, will show even greater differences between the responses in light and darkness. Our data suggest integration of visual and auditory information in which input from the eyes suppresses processing of information from the ear. This fits with the circadian pattern in evasive behavior we see in the lab in which stimuli that elicit robust, low threshold responses in the evening fail to trigger evasion in the afternoon.
