With a new decade upon us, science is at an all-time increase and still growing. Nowadays you can even attend interactive courses such as the Photometry Institute for more hands-on learning. If you are curious about what fiber photometry is and how this science field is being used to study animal behaviors, you are in the right place.
We are going to share everything we know about photometry in the article below.
What Is Fiber Photometry?
Fiber photometry is when scientists use fluorescent indicators to monitor signals in genetically-defined nervous systems in behaving animals. Scientists can measure the concentrations of calcium that freely behaving animals have. It can also monitor other molecules such as neurotransmitters.
In neuroscience, this is a method where optical fibers are implanted near the brain region that is being studied. The optical fibers deliver light and collect the data that is induced by calcium activity during the light excitation.
If the animals that are being studied are freely behaving animals then the setup for this photometry study includes a beamsplitter or combiner and the excitation light source. The beamsplitter separates the fiber optic rotary joint, the optical cannula, the fluorescence light, and the excitation. The fiber-optic patch cords, on the other hand, are connected.
You can find out more about using wireless fiber photometry right here. Wireless is an easier way to go when using it with freely moving animals because you do not have to worry about cords and cables. Cables prevent the animals from truly being themselves giving inaccurate testing many times.
Capturing Signals in Animals
To capture the signals in animals there is an optical fiber implanted into the region on the animal that is being studied. Then the other end of the fiber is placed on the photometry hardware. Once everything is connected a laser light source or an LED light source passes light through the fiber.
This light excites the indicator proteins in the target region. The fluorescent light then goes back through the fiber to a photodetector and keeps records of the changing concentrations in the animal and area being studied.
Why Fiber Photometry?
You might be curious about why fiber photometry is being used, the answer is because it helps researchers understand the links between behavior states in animals and the patterns of the neurons that are fired.
Scientists are also able to measure the changes in calcium levels when there are changes in the animal being studied.
A benefit that fiber photometry has is that it is fairly simple. In its simplest form, you are able to record from a population of neurons without any extra complications of spatial information. The components are pretty standard and easily available to buy. The output signals can then be digitized with equipment that is usually found in neuroscience laboratories already.
Another benefit is that the fibers are customizable. Fibers can be custom treated depending on the qualities that you want to achieve. Fibers can either be etched, painted, or tethered. This will give different geometric and optical qualities.
A third benefit of fiber photometry is that the fiber implants are less invasive. The fibers are usually between 240 and 480um. This is much smaller than other methods that use implants. Keep in mind that although it is less invasive because the fibers are thinner it means that you have to compromise on the recording area or lower signal levels.
Another benefit worth mentioning is that with this type of testing the photodiodes are extremely sensitive. No matter how low the photon count levels are the signals are picked up. This means that even low activity levels can be detected in an animal.
Last but not least because the size of the implant is so small, fiber photometry can record from multiple brain regions vs just one. Recording from multiple brain regions gives a bigger field of data to study and learn from. The more data that is collected the more in-depth the report will be, which will turn into a better understanding of the behavior of the animals being studied.
Although there are many benefits of photometry there are some cons as well. One of the biggest restrictions is that with some setups the fiber implant is directly connected to the detection hardware which makes it challenging when handling animals between chronic recordings. Some ethics authorities do not even allow this making it difficult to perform tests in certain areas.
Typically what is done to address this issue is that the animal is disconnected in between recordings by implanting a thin tube called a cannula and then lowering the fiber into the cannula during the recordings. This still makes it challenging because going from one experiment to the other you more than likely will not be able to find the same exact brain area.
Another solution to this restriction is to use wireless photometry modules. This combines on-the-probe detectors with micro LEDs and dichroic mirror components to test the subjects and eliminating the cable restriction. The key is to find a wireless solution that fits your needs.
Feeling Like a Photometry Pro?
Now that you know the ins and outs of what fiber photometry is and how it is being used in the science world today, you are full of plenty of knowledge.
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