Way back when I was a kid, I think this was when I was in Junior High or about 1972, my science teacher showed us a movie about how nerve impulses traveled up a nerve fiber. I remember that they took a live but "pithed" frog (they had destroyed the brain with a needle) and strapped it's leg onto a board. They had dissected out one of the nerve fibers in the leg and connected an electrode to the nerve. That electrode was then connected to an oscilloscope (an electronic device used to look at the shape of electrical signals. I know that all sounds pretty gross but all they showed us in the movie was the leg strapped down with the electrode coming out. Anyway, they also had a device that could be made to touch the frog's foot with a specific amount of pressure. They proceeded to touch the foot and show the signal that was detected in the nerve fiber.
Now most people think of a nerve signal traveling up a nerve fiber as a singular event. They think only one pulse travels up the nerve for any one event sensed by the nerve endings. After all, all the biology textbooks ever describe is how one pulse travels up the fiber. However, when the device touched the frog's foot a series of pulses were detected by the oscilloscope. What's more, the pulses were not regular. They were separated by varying spaces like the lines on a bar code. This is very similar to what radio control hobbyists call Pulse Code Modulation, or PCM. In PCM the differences in the spacing between a set of pulses provide information to the device on the receiving end, such as the R/C airplane. In addition, the pattern of pulses detected in the frog's nerve was repeated every time the device touched it with the same pressure. However, when the device was set to touch the foot with a different pressure, a different pattern was detected, which also showed up exactly the same every time that particular amount of pressure was applied. This is again similar to PCM in that the same pattern always means the same thing to the receiving end and different patterns mean different things. Usually different patterns in PCM mean to set the flaps on an airplane to a different angle, or to turn the wheels of a car to a different degree.