The dragonfly is a killing machine. They can use their 360° visual span to swoop down and devour their prey mid-flight with a 95% kill rate. They are superheroes- or maybe super villains – of the insect world. Incredibly biologically equipped, dragonflies have eyes with four or five opsins (in contrast to the human’s three), letting them register UV light as well as ‘normal’ light. They have wings that act like propellers of a helicopter, allowing them to individually manipulate the trajectory of each wing to switch directions rapidly in mid-flight. Ant-Man? Spider-Man? They really should have Dragonfly-Man. To illustrate this insect’s abilities, I invite you to google “dragonfly catching fly slow motion video,” or something of that sort. You will be amazed. Through examination of this surprisingly dangerous and deadly predator, a motivation for scientific research arises: What biological equipment does this predator have that makes it so deadly?
Well, to understand the neuroscience behind the behavior, l went to the literature. In 2012, a paper was published entitled, “Eight pairs of descending visual neurons in the dragonfly give wing motor centers accurate population vector of prey direction.” Long title, I know. This paper examined the neurons that run straight from the eyes to the flight motor centers of the dragonfly. This means that the neurons don’t even waste time traveling through the brain, they just go straight to the flight muscles. The results of the paper show that these neurons, aptly named the target-selective descending neurons (TSDNs), encode a population vector that is strongly correlated with the position of the target (the fly).
Above is an example of a population vector. A population vector contains data based on the firing rate of the neurons and can be used to deduce the most-likely direction of movement. Neurons that make up a population vector are direction-oriented, meaning they have a preferred direction and show more activity when their direction is favored. As seen above, the neuron firing rate and the direction of movement is calculated, and a most-likely direction of movement is solved for. A scientist can use these population vectors to predict and influence a direction of movement an animal will take.
The adjacent picture depicts the population vector found in the 2012 dragonfly paper, showing the preferred directions of the neurons and the firing rates at these preferred directions. The goals of my experiment are to monitor the activity of the TSDNs while changing the location of the fly around the dragonfly, and then to use this data to understand the neurons’ population vector. Based on the patterns of activation that I find, I will deduce the preferred direction of each neuron. After the data for the population vectors is collected, I will try to stimulate a TSDN (with a known preferred direction) and see if and how this stimulation influences the direction of movement of the dragonfly. So that is what I’ll be doing for the next 10 weeks! My next challenge…catching some samples! I will keep you updated!
By Patricia Aguiar