The movement of nerve impulses through neurons observed for the first time thanks to a new ultrafast camera

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To carry out all of our metabolic functions, transmitting a sensation or generating a mechanical response, our nervous system must constantly process a large amount of information. These take the form of nerve impulses (electrical impulses) and move at a very high speed through our neurons. The speed is such that the phenomenon could never be observed directly. Using the latest advances in high-speed photography, Caltech engineers have designed an ultrafast camera capable of capturing the movement of electrical impulses through neurons. Observing this previously elusive phenomenon could lead to a better understanding of the biology of the brain, critical in the search for neurological treatments. Electromagnetic signals traveling at the speed of light could also be captured.

To provide a sensation (such as touch, for example) through our peripheral nervous system, a whole cascade of information transmission to the central nervous system takes place. The nerve impulse passes through the neural cells of the spinal cord to reach those of the thalamus, the sensory processing center located deep in the brain. The latter, thanks to its more than 100 billion neurons, then defines an appropriate response according to the information received.

These complex interactions involving many neurological functions take place extremely quickly. The nerve impulses transmitted through the sensory nerves move in particular at almost 160 kilometers per hour. Sensations that require immediate responses (such as a burn) can generate nerve impulses even faster, traveling up to 300 miles per hour.

Medical imaging technologies, such as fMRI, can indicate that brain regions are activated (by depolarization) by stimulation of nerve impulses. Nevertheless, ” Observing nerve signals is critical to our scientific understanding, but has not yet been achieved due to the lack of speed and sensitivity of existing imaging methods. Lihong Wang, co-senior author of the new study described in NatureCommunicationsand a researcher at the Caltech Optical Imaging Laboratory.

For the first time, the movement of these nerve impulses through axons could be captured using a camera using differentially enhanced compressed ultrafast photography (Diff-CUP) technology. In fact, Wang’s research team previously developed the CUP imaging system to be able to capture laser pulses (which travel at the speed of light) and record video at 70 billion frames per second. The Diff-CUP combines this system with a device called a Mach-Zehnder interferometer, to capture sensory nerve impulses.

Imaging signals propagation in peripheral nerves is the first step Wang says.” It would be important to image live traffic in a central nervous system, shedding light on brain function. “, he suggests.

Nerve impulses traveling at very high speed through the axons, captured by the Diff-CUP camera. ©Caltech

A high-speed imager coupled to an interferometer

Thanks to the Mach-Zehnder interferometer, the new Diff-CUP camera can capture fast-moving objects by splitting a beam of light in two. Only one of the two fragments passes through the object to then recombine with the first and exit. As light waves are affected by the materials that make up the objects they pass through, the beam that passes through the object is desynchronized from the one that does not pass through it (with which it recombines on leaving). This desynchronization induces interference whose patterns reveal information about the object.

In other words, this type of interferometry has also been used for the detection of gravitational waves, and its coupling with CUP allows the capture of images at incredibly high speeds. To test their technology, the researchers filmed electrical impulses traveling through a frog’s sciatic nerve (Xenopus laevis) — moving at about 100 meters per second. The motion of electromagnetic pulses through a lithium niobate crystal (at the speed of light) has also been successfully captured.

Source: Nature Communications

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