Have you ever inhaled helium from a party balloon? Go ahead, admit it. It’s funny, right? You laugh because your voice is so high-pitched, it doesn’t sound like you anymore. Maybe you try to make your voice lower-pitched to counteract the effects of the helium. This is just a fun example, but really we humans are lucky: most of us are able to recognize our own voice and control it accordingly (except males in early puberty, sad!). But how are we able to differentiate between our own voice and others’ voices?
My project is one part of many that seeks to identify the neural circuitry behind recognizing self-produced sounds and differentiating them from the external environment. Since humans are expensive to work with, and there are, yknow, ethical concerns to sticking a single-cell electrode into a human’s brain, my lab works with songbirds and, you guessed it, MICE!
When mice mate, the male releases ultrasonic vocalizations in communication with the female that can only be detected by humans using a software called Spike2 and a very fancy microphone. I put the male and female in a chamber together and either fill the chamber with normal air or heliox, depending on the session and whether the male animal is a control animal or an experimental animal. I then record their mating vocalizations for 20 minutes while coding what specific mating behavior (grooming, rear sniffing, etc) they’re doing every 10 seconds. After running the sound files and behavioral data through Matlab programs, I enter a whole bunch of data into a massive Excel spreadsheet, including the proportion of each behavior per session and mean pitch of the vocalizations per behavior per session.
With my project, I essentially hope to answer two main questions: 1. Do the proportions of the various mating behaviors change significantly when the mice are in heliox as opposed to normal air? 2. For each animal, I record a baseline of 5 sessions in normal air. Then, I run them through 8 sessions in heliox, and finally, 8 sessions in normal air again. Is the mean pitch of the vocalizations in the last 8 air sessions any different from the 5 baseline air sessions? If the mean pitch is lower in the last 8 sessions, does this signal that the mice were trying to purposely lower their voice in the helium sessions, and the habit spilled over to the last 8 air sessions? DO THE MICE HAVE A CONCEPT OF THEIR OWN VOICE? *insert spiderman pointing at spiderman meme* Ongoing work in the lab involves placing electrodes into the mouse brains to record the electrical signals of particular neurons, specifically the neurons involved in the auditory-vocal motor pathway. Demonstrating activity of these connecting cells during vocalizations (with and without helium) will give us insight into the neurobiology behind recognizing and regulating our own voice.
Circling back to the bigger picture of my lab’s research, the ability to distinguish between self-produced sounds and external sounds is something most of us can take for granted. But some of us aren’t so lucky. Individuals with schizophrenia or other mental illnesses with psychosis have trouble differentiating between the voices in their head and real voices of other people. Their ability to recognize self-generated sounds is impeded, and by researching the neural circuitry behind the connection between auditory and vocal motor areas in mice, we hope to eventually target similar areas in humans.