Executive Summary

Executive Summary:

The UC San Diego Department of Neuroscience is world-renowned and is one of the largest in the nation.  The department has developed significant partnerships with the Scripps Research Institute, the Sanford/Burnham Institute, and the Salk Institute to conduct some of the most unique and technologically advanced neurological research that is being performed today.  The program consists of a collaboration of clinical and neurological researchers who pursue the diagnosis, management, and research of neurodegenerative diseases.  Specifically, the department and our sponsors, Dr. Pavel V. Belichenko, PHD, MD, and Alexander M. Kleschevnikov, PHD, are dedicated to research in the field of Down Syndrome.

            Down Syndrome can reduce the cognitive and speaking abilities of an individual affected by the disorder.  These effects can also be seen in mice and measuring their ultrasonic vocalizations (USV’s) can show the differences in language abilities of mice affected by Down Syndrome and normal mice.  These differences include changes in frequency range and how the mice react to new environments.  The goal of this project was to be able to record and analyze the USV’s of mice in different behavioral settings.  This project also provides a “Y” shaped maze to conduct these behavioral experiments.

            The final design of the project contains three major components.  The first component of this project is the microphone that is used to record the mice during experimentation.  The microphone selected was the Ultramic 250K (by Dodotronic) because of its price and ability to link to a computer through USB.  While the microphone did not have a perfectly flat frequency response, it was determined that it was capable of recording all ranges of USV’s (20-100kHz), but has reduced sensitivity in the 70-100 kHz range based on tests using a known signal. This reduction of sensitivity can be seen in the graph provided by Dodotronic shown in Figure 1. The microphone will likely not be able to capture all signals emitted by mice throughout all points of the maze because of this reduced sensitivity, therefore, future iterations of this project should use higher quality microphones or an array of multiple microphones. Mice were also recorded in different situations for preliminary analysis and to further determine if the microphone was functional for the purpose of this project. The mice that yielded the best results were a male and female together, two males together, and a mother and her pups. These recordings further increased concern of the microphone's sensitivity as the adult mice would often emit signals in the frequency range with reduced sensitivity.

Figure 1: Frequency Response of the Ultramic 250K

           The second component of this project was the “Y” shaped maze that the behavioral test take place in as seen in Figure 2.  The Y-maze was built to specifications provided to us by the sponsors of this project and later modified for stability as well as to ensure that the mice could not escape during testing.  The maze is comprised of 0.635 cm (0.25 in) acrylic and each “leg” is 38.1 cm (15 in) long and 25.4 cm (10 in) tall.  A 5.08 cm (2 in) base, brackets, and “puzzle” cuts were incorporated to make sure the structure was rigid enough for multiple uses.  Sensors were also added to the maze (two on each leg) so that data could be collected on the location of the mice during the experiments. A passive infrared sensor was first tested, but was found to have an unacceptably long settling time. Ultimately an infrared LED and phototransistor were used as motion sensors for their short settling time and ability to function through layers of clear acrylic.

Figure 2: Y-Maze Leg (with Puzzle Design)                                                                                                                             Figure 3: Final Y-Maze

    The final component of this project was the program created in LabView to record and analyze audio files, as well as play video files and collect data from the sensors. The recording program was found to be fully functional and does not create any delays between user input and the start of the recording.  The audio analysis program provides information on the frequency and amplitude of the USV’s over time and can be compared with video files of the experiment using the video playback.  The sensor program also allows the user to identify the location of the mice during experimentation, which can also be compared to audio and video files.  An example of the audio analysis user interface can be seen in Figure 4.  Overall, the program is intuitive and allows for the accurate recording of data that can be used by researchers in this particular field of study.

Figure 4: Audio Analysis Interface (LabView)