A freshly discovered unique form of messaging between the cells of the human brain may mean that it is even more productive than previously thought.
An international team of scientists from Greece and Germany found in cortical cells located on the surface of the cerebral cortex a mechanism that independently generates a new “graded” signal. This may give individual neurons a different way to perform their logical functions. An article about it was published In the Science magazine.
The brain is often compared to a computer. This is a very crude analogy, but when describing how signal transmission inside the brain works, it has a right to life to a certain extent. Both of them use the power of electric voltage to perform various operations.
In computers, this happens in a simpler way: the flow of electrons passes through transistors, a kind of “control panel” of the current in the circuit. In neurons, the signal is transmitted using membrane channels that exchange ions of elements such as sodium, chlorine and potassium. This impulse is called the action potential.
When activated from the neuron to its neighbor, sodium ions go through the synapse: this is how the signal is transmitted. However, as it turned out, the brain still has surprises for scientists. Researchers tested electrical activity in brain tissue samples from patients with epilepsy. By analyzing the structure of these sections using fluorescence microscopy, they saw that individual cortical neurons exchanged calcium ions upon activation.
It turned out that in this way, previously unregistered brain waves are triggered – calcium mediated dendritic action potentials (dCaAP). To make sure that this is not an error in the measurement, not an accident or a unique feature of the tissues of people with epilepsy, the authors of the article double-checked their results on other tissues of the cortex – sections of brain tumors.
In addition, the use of a sodium channel blocker did not lead to a complete cessation of signal exchange: the final “silence on the air” was achieved only with the blocking of both sodium and calcium.
What does this mean? If we continue the analogy with a computer, then instead of transistors, the brain uses dendrites – branching processes of neurons. The more “distributor” dendrite, the more information it can process. “Dendrites play a central role in understanding the brain because they underlie what determines the processing power of individual neurons,” explains neuroscientist Matthew Larkum.
Dendrites are a kind of “traffic light” along the path of nerve impulses. If the action potential is large enough, the activation of the following neurons occurs, which can further block or transmit a message, but if they do not, activation does not occur. This is the logical foundation of the work of our brain – voltage surges provide information transmission through logical commands of the type AND (if AND x, AND y are triggered, the signal is transmitted) and OR (x OR y must be triggered for signal transmission).
In addition to AND / OR logic functions, these neurons can generate XOR (“exclusive OR”) logic commands that enable one signal to go further along the chain of neurons if the other signal meets certain conditions. “Previously it was believed that XOR operations require network solutions,” the scientists explain.
To make sure that neurons really behave this way, researchers used a method of fixing potential called somatodendritic patch clamp. It consists in establishing close contact of the polished glass microelectrode with a single neuron (its dendrite) and the removal of potential from it. This allowed us to study the tissues of the deep (second and third) layers of the cortex. It is here that the biological basis of higher-order mental functions is located, which are associated with sensations, thinking and motion control. The device helped to see the potentials of dendrites and record the signals transmitted by individual neurons upon activation.
More research is needed to find out how dCaAPs manifest themselves in all neurons and in the living system as a whole. In addition, it is still unknown whether such signals are unique to humans, or appeared much earlier on the path of evolution. In any case, this discovery can bring a lot of benefits both in relation to the study and treatment of the brain, including problems of higher functions, and as an inspiring example for engineers. Perhaps new discoveries of the constructive capabilities of the brain will help in the work on the creation of new devices.