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Implanted electrode recordings from a praying mantis auditory interneuron during flying bat attacks

Jeffrey D. Triblehorn* and David D. Yager

Department of Psychology, University of Maryland, College Park, MD 20742-4411, USA



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  		Fig. 1. The implanted electrode arrangement in the hanging tethered mantis preparation. Scale bar, 10 mm. The right-hand wire holds the clip electrode and the connective, the middle wire holds the indifferent lead and the left-hand wire stabilizes the mantis in a ‘flight-like’ posture.

 


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  		Fig. 2. Diagram of the flight room (6.4 mx7.3 mx2.5 m) and the experimental arrangement for the bat attack experiments. The gray box represents the calibration space for the high-speed video cameras (2.2 mx1.9 mx1.6 m). The dashed lines illustrate the two typical flight path types for the bat attacks (direct approach, blue line; indirect approach, red line).

 


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  		Fig. 3. Example of the changes in different bat vocalization parameters during an attack sequence from one trial. The shaded areas mark the beginning and end of the approach, buzz I and buzz II phases. In the approach phase, pulse repetition rate (PRR) is consistent, pulse durations are over 3 ms and the bandwidth of the echolocation vocalizations is broad (based on the beginning and end frequencies). In the buzz I phase, PRR increases and pulse duration decreases. In the buzz II phase, PRR is over 100 pulses s–1, pulse duration continues to decrease, the sweep rate increases and the bandwidth of the echolocation vocalizations narrow. In the beginning of the buzz II phase, the relative amplitude of the echolocation vocalizations increases (probably as a result of the bat approaching the microphone located near the mantis target), but the relative amplitude drops in the second half of the buzz II phase (approximately 100 ms before contact).

 


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  		Fig. 4. (A) Example of an electrode implant recording (upper) with the corresponding bat vocalizations taken from the bat detector (below). The responses of 501-T3 are in red. 501-T3 responses occur only after a bat vocalization, and each vocalization elicits a 501-T3 response, indicating that the interneuron can encode the bat’s pulse repetition rate. Time scale, 50 ms; voltage scale, 20 mV. (B) Same recording with the time scale expanded to illustrate that the responses of 501-T3 (in red) to a single bat vocalization contain multiple spikes. The first spike in each burst of 501-T3 activity has a larger amplitude than the following spikes because of its very high phasic firing rate. Time scale, 10 ms; voltage scale, 20 mV.

 


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  		Fig. 5. Example of a B1 flying bat attack trial. The upper trace is the neural recording and the bottom trace the corresponding bat vocalizations taken from the bat detector. The responses of 501-T3 are in red. The different phases of the bat attack are indicated. Time scale, 50 ms; voltage scale, 10 mV.

 


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  		Fig. 6. (A) The bat pulse duration (red line, no symbols, left axis in ms), pulse repetition rate (PRR; red line/circles, left axis in pulses s–1) and 501-T3 spikes per burst (blue line/circles, right axis) for the corresponding B1 trial in Fig. 5. The top axis is distance to contact (cm). OS, out of the calibrated space. 501-T3 burst responses cease before the buzz II phase begins (indicated by the right-hand dotted line). (B) A comparison of the bat PRR (red line/circles, in pulses s–1) with the burst rate of 501-T3 (blue line/triangles, in bursts s–1) to illustrate accurate following of bat vocalization emissions by 501-T3 during the stable approach phase and into the buzz I phase until responses cease entirely.

 


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  		Fig. 7. Example of a B2 flying bat attack trial. The upper trace is the neural recording and the bottom trace the corresponding bat vocalizations taken from the bat detector. The different phases of the bat attack are indicated. Time scale, 50 ms; voltage scale, 10 mV.

 


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  		Fig. 8. (A) The bat pulse duration (red line, no symbols, left axis in ms), pulse repetition rate (PRR; red line/circles, left axis in pulses s–1) and 501-T3 spikes per burst (blue line/circles, right axis) for the corresponding B2 trial in Fig. 6. The top axis is distance to contact (cm). OS, out of the calibrated space. 501-T3 burst responses cease before the buzz II phase begins (indicated by the right-hand dotted line), but single-spike responses continue into the buzz II phase; these cease before contact. (B) A comparison of the bat PRR (red line/circles, in pulses s–1) with the burst rate of 501-T3 (blue line/triangles, in bursts s–1) to illustrate accurate following of bat vocalization emissions by 501-T3 during the stable approach phase and into the buzz I phase. Although 501-T3 continues to respond to bat vocalizations into the buzz II phase, accurate encoding of bat PRR breaks down before the transition from the buzz I phase to the buzz II phase (indicated by the decrease in 501-T3 burst rate before the buzz II phase).

 


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  		Fig. 9. Summary of the time and distance to contact for the last burst response (diamonds) and the last single-spike response (crosses) for both B1 (red symbols) and B2 (blue symbols) trials. The last burst responses for B1 and B2 trials form a cluster. The last single-spike response for B1 trials also falls within this cluster. However, the last single-spike response for B2 forms a separate cluster.

 


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  		Fig. 10. Summary of the pertinent events in the bat attack vocalization sequence (red, right) and the corresponding 501-T3 neural events (dark blue, left) and mantis evasive behavior latencies (light blue, left). 501-T3 ceases producing burst responses and accurately following bat pulse repetition rate (PRR) during the buzz I phase, and this correlates well with the latency for the diving portion of the mantis evasive response.

 


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  		Fig. 11. Range of intensities at a range of distances from the 501-T3 preparation for all vocalizations for the stationary bat. The bars indicate the median intensity at each distance. Although there is considerable overlap, there is a general decrease in vocalization intensity as distance increases.

 


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  		Fig. 12. Number of 501-T3 spikes per burst elicited by bat vocalizations at different intensities for two mantids in the stationary bat vocalization experiment. Responses are separated into vocalizations 3 ms and longer (purple triangles) and those less than 3 ms (green triangles). For PAR-17-16, 269 of the 311 vocalizations shorter than 3 ms and 26 of the 87 vocalizations of 3 ms or longer between 50 and 65 dB pe SPL did not elicit a response, and their data points overlap. For PAR-16-36, the only large overlaps are at 69 dB pe SPL (no response) for vocalizations of less than 3 ms (five cases) and at 57 dB pe SPL (no response) for vocalizations of 3 ms or longer (six cases).

 


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  		Fig. 13. Percentage of 501-T3 responses (either single-spike or multi-spike bursts) to vocalizations of different intensity ranges for pulses 3 ms and longer (purple circles) and pulses less than 3 ms (green circles). The numbers in parentheses indicate the number of vocalizations at each intensity (purple for pulses 3 ms or longer, green for pulses less than 3 ms). 501-T3 responds more reliably to longer bat vocalizations (durations of 3 ms or longer) at all intensities except those that are very loud (>90 dB pe SPL) or very quiet (<60 dB pe SPL).

 


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  		Fig. 14. Diagram showing whether a response of 501-T3 to a bat vocalization was a multi-spike burst (squares) or a single spike (circles) for pulse durations of 3 ms or longer (purple lines) and pulse durations of less than 3 ms (green lines).

 

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© The Company of Biologists Ltd 2002