Analysis of rodent ultrasonic vocalizations
using the TDT system II
R.E. Brown, S. Kehoe and S. Turner
Department of Psychology, Dalhousie University, Halifax, Nova Scotia, Canada
While the analysis of human speech and birdsong is very advanced, that of rodent ultrasonic vocalizations (UVs) is more primitive because researchers cannot detect ultrasound without specialized equipment. The ultrasonic vocalizations emitted by rodents are signals in which the primary frequency lies above the audible range of humans (typically between 20 and 130 kHz). Bat detectors have been used to visualize and count UVs, but a more advanced system is required for analyzing rodent UVs into 'syllables', 'words' and 'phrases'.
We have developed a system that uses the Tucker-Davis Technologies (TDT) System II for recording, storing and analyzing ultrasonic vocalizations. Ultrasounds emitted by mice and rats are detected and transduced to electronic signals by an ultrasonic microphone. A 20 kHz high-pass filter is used to remove frequencies below 20 kHz. The filtered signals are converted to a digital signal using a TDT Analog-to-Digital module. The digitized signal is recorded to a computer hard drive and Fast Fourier Transforms are performed on each pulse by the System 2 to provide frequency data. The recorded data is analyzed in LabVIEW to determine pulse length, pulse frequency, and the number of vocalizations within a 1-5 minute test period. Means, medians and standard deviations are calculated for both the vocalization length in ms and the frequency in kHz.
The recording process is controlled using software written in Visual C++. Using this system, each ultrasound is counted, categorized by frequency and stored. The signals can then be edited and played back using a TDT digital-to-analog module. We can examine the ultrasonic vocalizations of rodents and compare the effects of age, sex, species and experimental treatment on different parameters of UVs, and then play them to other animals to determine their responses to whole and edited vocalizations. This system will allow us to advance the study of rodent ultrasonic vocalizations in new ways that are not possible using bat detectors.
Poster presented at Measuring Behavior 2002 , 4th International Conference on Methods and Techniques in Behavioral Research, 27-30 August 2002, Amsterdam, The Netherlands