In 1928, Edgar Adrian , Nobel Laureate in Physiology or Medicine in 1932, was the first person to be able to hear the secret language of neurons.
To do this, he uncovered a set of axons from the brain of an anesthetized rabbit. He separated all the axons and placed an electrode on them at least two or three. Adrian saw an electric shock every time the rabbit breathed .
Finally, Adrian attached a speaker to the electrode, and then he began to hear a kind of clicking sound, like the quick thumps of Morse code . The noise was an electrical signal.
That electrical signal Adrian was listening to was an action potential, the basic unit of neural communication. This is how Eric Kandel explains that it is produced in his book The New Biology of the Mind :
The inside of the membrane that surrounds a neuron and its axon have a slight negative electrical charge relative to the outside. This charge is due to an uneven distribution of ions (electrically charged atoms) on either side of the cell membrane. Because of this uneven distribution of ions, each neuron is like a tiny battery where a small amount of electricity is stored and released at any given moment.
The rapid discharge of energy causes the neuron to generate an action potential. This electrical signal spreads rapidly throughout the neuron, from the cell body to the end of the axon. Everything we see, touch, hear and think begins when those spikes of electricity rush through the neuron from one end to the other .
Later, Adrian would record electrical signals from individual axons in a toad’s optic nerve. In addition, he amplified the signals so that they could be viewed on an old oscilloscope, as if it were a two-dimensional graph.
He also discovered that a neuron does not indicate its intensity by modifying the strength or duration of its action potentials (it is not the same to distinguish the friction of the skin as a strong blow or a dim light from a bright one). The intensity was revealed by varying the frequency with which it generated the action potentials . A weak stimulus causes the cell to generate only a few potentials, while a strong stimulus produces much more frequent impulses.