The Backyard Brains Heart and Brain SpikerShield is pretty amazing-you can use it to look at both the electrical activity of your heart (across your wrists even!) and the rhythmic electrical activity of your brain. As with all our products however, this wasn’t good enough for us, so we’ve been developing even more experiments for it!
You may have seen our recent experiment looking at the human EOG (ElectroOculoGram). It turns out that the eye forms an electric dipole, where the front is more positively charged and the back more negative. When you move a dipole, such as the eye, it creates an easily observable (at least, with our H&B SpikerShield) electric potential deflection. Based on the direction of deflection (positive or negative) it’s even possible to tell which direction the eye is moving in! It’s easy to set up and requires no additional equipment beyond the H&B Bundle.
How strong of a deflection can you or your students create? Can you tell where someone’s looking just from the potential their eye generates? Grab one today to explore this fascinating intersection of neuroscience and physics.
Over the course of the next 10 weeks, I will be designing and running a neuroethological study on the electrical behavior of the South American weakly electric fish. My goal is to develop a Backyard Brains-esque tool to listen to, record, and manipulate the electrical discharge of the electric fish. I will be posting routine updates on my progress, documenting the successes and failures that I run into along the way.
For some basic background, weakly electric fish are capable of generating electric fields which allow them to navigate the environment and communicate with other electric fish.
Eigenmmania Virescens – Glass Knifefish (Photo by. Nadia Milan)
Weakly electric fish have an electric organ, typically located in their tail. This is what allows them to generate electric signals, also known as Electric Organ Discharge (EOD). These electric signals are in the range of millivolts and are used to communicate with other fish and in electrolocation, a process of navigating the environment by means of detecting objects and sources of external electric fields. What separates weakly electric fish from strongly electric fish is the strength of the EOD – strongly electric fish such as electric eels and rays can use their EODs to stun prey or defend themselves.
Electric Organ Discharge?
When in close contact with another fish emitting a similar frequency, weakly electric fish are effectively “blinded” (Watanabe & Takeda, 1963). In order to cope, the weakly electric fish has developed a jamming avoidance response (JAR) in which the fish will adjust their emitted frequencies to diminish electric field disturbances. For example, if two fish emit signal frequencies of 300 Hz and 304 Hz, the beat frequency will be too low (4 Hz) and cause too much interference between the fish. In this case, the fish with the lower frequency might push its frequency down to 292 Hz while the other pushes its frequency up to 312 Hz, resulting in a more ideal beat frequency of 20 Hz.
I plan to experiment with the JAR to further understand the neural mechanisms of these fish – I plan to stimulate the water to mimic the presence of other fish in the tank as a means to investigate. I would like test out the absolute range for these fish and figure out how to reliably set a fish at a certain frequency. There are many more interesting aspects of the weakly electric fish that I have yet to talk about, so stay tuned for more!
By. Davis Catolico
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