This summer I continued a long term project in Marc Schmidt’s lab exploring the zebra finch song system. This past spring I completed an independent study looking at how sensory feedback from the respiratory system affects higher level motor control regions of the bird’s cortex. I worked specifically with premotor nucleus HVC, which is important for song production in the finch. The birdsong literature has already shown that HVC is sensitive to sensory information, responding robustly to altered playback of birds own song. The thinking in the field is that HVC works as an error correction gate on song, taking in sensory information and acting on downstream motor control nuclei to correct for errors. Our hypothesis is that since HVC is responsive to auditory information, it may also be responsive to other kinds of sensory information, like air sac pressure—the equivalent of lung pressure in mammals. Production of song in the finch requires complex coordination of respiratory and syringeal – the syrinx being the songbird’s vocal organ, equivalent to our larynx—muscles. My experiment involves disrupting air sac pressure in order to create an error in viscerosensory feedback to HVC. The hope of the experiment was to find a robust response in HVC to that pressure change.
One key element of my project was the behavioral state of the animal. My lab has done similar experiments to these in the anesthetized bird but never in awake or lightly sedated animals. In anesthetized animals the response in HVC is sparse and difficult to find. In my experimental setup I did not use anesthesia, but simply sedated the bird with some diazepam (Valium) and puffed small bursts of air into the bird’s air sac through a soft plastic tube while measuring electrical activity in HVC. I found that in a pool of 12 birds, 8 showed at least one response (67%) and in a pool of 130 sites in HVC across all birds, 20% showed robust responses in HVC.
One problem I encountered was that halfway through the summer I stopped getting any response at all. I did experiments in four birds with no success, going from a 36% response rate to a 2% response rate. The key difference between these last four birds and the first eight that showed responses was that between these two sets, I switched to a new bottle of diazepam. I suspect since diazepam is known to affect breathing, this new diazepam could possibly be silencing the effect I was seeing previously.
Overall this summer I learned a great deal about the experimental method as well as how many variables there are to account for. Because of this I was very conservative in my analysis of the data and spent a lot of time looking closely at the raw data in an attempt to understand it better. I am proud of the work I did this summer and grateful to CURF for giving me this opportunity. I am especially excited because after some more extensive analysis and a few more experiments, I will be presenting at the Society for Neuroscience conference in D.C. this November, which will be valuable for my future in research.