Researchers from the Howard Hughes Medical Institute have developed a novel imaging technique that allows us to peer into the brains of a living zebrafish and witness the activity of almost every single neuron as the organism thinks and moves. And the result is simply mesmerizing.
Published in the journal Nature Methods, researchers describe how the new technique, which has been dubbed light-sheet imaging, allowed them to simultaneously visualize and record the activity of 80% of the neurons within the brain of larval zebrafish. It is hoped that this new technique will allow researchers to study the neural mechanisms of behavior in unparalleled detail.
For the technique, researchers married genetic engineering with optics to observe the firing activity of around 80,000 neurons. The scientists modified the zebrafish so that their neurons expressed a chemical indicator that rapidly fluoresces as the cells fire. Zebrafish are ideal organisms for this kind of study because the larvae are transparent and their brains are small enough to be observed under the microscope.
The researchers then guided laser beams through the fish which caused the neurons to glow. By placing a video camera over the experiments, they were able to record the neuronal activity with incredible detail, which is shown in the clip below:
At the start of the experiment, we can see that the forebrain (far right) is twinkling like fireflies. This was when the fish was resting and likely represents the fish’s thoughts at that particular time. Then, activity rapidly sweeps through the brain like wildfire. This corresponds to the moment when researchers created the illusion that the fish was drifting backwards, sparking a wave of activity that resulted in the initiation of swimming.
As mentioned, this exciting technique allowed the researchers to observe around 80% of the neurons in the zebrafish brain in real-time. Furthermore, the researchers are able to identify the neurons that are associated with a particular behavior. Unfortunately, however, it is currently unable to determine the number of times that neurons fire.
While impressive imaging techniques have been developed before, this is the first time that researchers have been able to record and visualize activity in virtually the entire brain whilst an animal is thinking and moving.
Whether information from studies on this model organism can be extrapolated to other vertebrates is unclear at the moment, but scientists are working towards the completion of a brain activity-behavior catalog.