Scientists have identified a unique form of cellular messaging that occurs in the human brain. It reveals how much we still have to learn about its mysterious inner workings.
Intriguingly, this discovery suggests that our brains may be even more powerful computational units than we realised.
In 2020, researchers from laboratories in Germany and Greece reported that cells in the brain’s outer cortex have a mechanism for independently generating new “grade-based” signals that could provide individual neurons with another way to carry out logical functions.
By measuring electrical activity in tissue slices removed during surgery from epilepsy patients and analysing their structure using a fluorescence microscope, neuroscientists have discovered that individual cells in the cortex “fire” using not only the usual sodium ions but also calcium.
This combination of positively charged ions generated a previously unseen voltage wave called a calcium-mediated dendritic action potential (dCaAP).
The brain, especially the human brain, is often likened to a computer, and although this analogy has its limitations, at some level the brain and computers perform tasks in a similar way.
Both use the power of voltage to perform various operations, and in computers, this takes the form of a simple flow of electrons through intersections called transistors.
In neurons, the signals come in the form of waves of opening and closing channels that exchange charged particles such as sodium, chloride, and potassium. These pulses of ion flow are Action potential.
Instead of transistors, neurons manage these messages chemically at the tips of their branches, called dendrites.
“Dendrites play a central role in understanding the brain, as they are the core that determines the computational capacity of single neurons,” say the neuroscientists from Humboldt University. Matthew Larcombe told Walter Beckwith: The paper was presented at the American Association for the Advancement of Science in January 2020.
Dendrites are the signalling devices of the nervous system: if the action potential is large enough, it can be transmitted to other neurons, which can then block or pass on the message.
This is the logical foundation of our brains, ripples of voltage collectively transmitted in two forms. and Message (if x and When y is triggered, the message is passed) or or Message (if x or When y is triggered, the message is passed on.
Perhaps nowhere is this more complex than the densely wrinkled outer part of the human central nervous system, the cerebral cortex. The deep second and third layers are particularly thick, packed with branches that carry out higher-order functions related to sensation, thought, and motor control.
The researchers took a closer look at the organization of these layers, hooking up cells to a device called a somatodendritic patch clamp, which allowed them to send action potentials up and down each neuron and record the signals.
“When I first observed dendritic action potentials, it was a real ‘Eureka’ moment.” Larcom says..
To ensure that their findings were not specific to people with epilepsy, the researchers double-checked their results in a small number of samples taken from brain tumors.
The research team had been conducting similar experiments To the mouseThe types of signals they observed buzzing through human cells were very different.
More importantly, when they treated the cells with a sodium channel blocker called tetrodotoxin, the signal was still detected — only by blocking calcium did everything go quiet.
The discovery of calcium-mediated action potentials was intriguing enough in itself, but modeling how this new sensitive type of signal works in the cortex revealed something surprising.
Logical and and orIn the type function, these individual neurons ‘Exclusive’ or (Exclusive OR)intersectionThis will only allow a signal if another signal is graded in a particular way.
“Traditionally, Exclusive OR It has been thought that network solutions are necessary for operation.” The researchers.
Further research is needed to explore how dCaAP works across neurons and within living systems, not to mention whether it is unique to humans or whether a similar mechanism has evolved elsewhere in the animal kingdom.
Technology is even looking to our own nervous systems for inspiration in developing better hardware: learning that our own individual cells have a few more tricks up their sleeves could lead to new ways of networking transistors.
How this new logical tool packed into a single neuron translates into higher-level functions is a question for future researchers to answer.
This study Science.
A version of this article was originally published in January 2020.
