Finalizing a No-Harm, Dragonfly Visual Neuron Recording Prep
Welp, it’s my last day of work here at Backyard Brains! It’s been a fun 11 weeks with my fellow interns, but all things must end. Last week we wrapped up all the TED filming for our mini series episodes. I had a great time, and I’m really looking forward to seeing the final result.
The dragonfly project ended in a good place; we have a good amount of data from the final setup and succeeded in developing a replicable, recoverable prep. I take a dragonfly that has been in the fridge for a few hours and carefully restrain its wings back with a “helping hands” clamp covered in cloth. This prevents damage to the wings. Then I wrap the dragonfly with a cloth, leaving only its head exposed; this is so the dragonfly doesn’t move and pull out the electrode wires during recording. The cloth is taped and pinned into the clamp’s cloth to hold it in place. Then, I still use silly putty to place and hold the electrode’s stick in place so the wires don’t come out when I prepare the recording electrodes and move the Dragonfly later.We modified one of the Backyard Brains Micromanipulator electrodes so that instead of a grounding pin, we use a reference electrode. Then, onto the dragonfly, I place the two electrode wires on either side of a single, exposed ventral nerve cord.I also made a few new stimuli, all on generic size paper. One had a fake plastic fly glued to the middle, and the other four I drew various sizes of dots in the center: 3mm, 7mm, 2.3cm, and 9cm in diameter.
I waved these papers by hand left and right, up and down, and even switched them out in the same recording to compare size preferences, not just direction. Besides just seeing a reaction, I’m interested in seeing the directionality of response.
This indicates that there are certain neurons within the dragonfly’s nervous system, like the target-selective descending neurons (TSDNs), that help the dragonfly differentiate, in an almost mechanical way, what direction a target is moving. This has the advantage of removing some “post processing” of the information, allowing the dragonfly to react quicker and hunt its prey more efficiently. I had success in seeing this kind of evoked response in my trials, which was a great success for the project.
As you can see in the results above, as I improved my prep and experimented with new electrodes, I began to see better results. By the end, I was seeing responses in most of my preps. I began to observe a directional bias more frequently and began seeing more evidence of a size discriminate response. By the time we presented our projects via a poster presentation on August 2nd, I had totaled my data into success rates of getting certain kinds of signals using this final prep I developed, giving students who repeat this experiment an idea of how difficult or easy it will be to see different responses.
Further, we are hoping to publish these results, but in order to do so, the stimuli cannot be moved by hand; the human error of timing the event markers in Spike Recorder with the movement of the stimulus is not accurate or consistent enough for a peer-reviewed journal. We built a servo-motor rig that moves the paper back and forth while simultaneously sending the event markers to the software. The rig has a lot of problems, and I ran out of time to work on it, so if my project is continued next summer, the rig should be the focus to really iron out the automation and precision of stimulus delivery.
That’s all from me! Thanks for reading. Dragonfly girl, signing off.