Scientists have identified a unique form of cellular messaging that occurs in the human brain, revealing how much we still have to learn about the mysterious inner workings.
Excitingly, the discovery hints that our brains may be even more powerful computing units than we realized.
In 2020, researchers from institutes in Germany and Greece reported a mechanism in the brain’s outer cortical cells that produces a new ‘self-sorting’ signal, one that can provide individual neurons with another way to carry out their functions. their logical
By measuring electrical activity in sections of tissue removed during surgery from epileptic patients and analyzing their structure using fluorescence microscopy, neurologists discovered that individual cells in the cortex used not only the usual sodium ions to ‘fire’, but also calcium .
This combination of positively charged ions initiated never-before-seen voltage waves, referred to as a dendritic calcium-mediated action potential, or dCaAP.
Brains – especially those of the human kind – are often compared to computers. The analogy has its limits, but on some level they perform tasks in similar ways.
Both use the power of an electrical voltage to perform various operations. In computers it is in the form of a fairly simple flow of electrons through junctions called transistors.
In neurons, the signal is in the form of a wave of opening and closing channels that exchange charged particles such as sodium, chloride and potassium. This pulse of flowing ions is called an action potential.
Instead of transistors, neurons manage these messages chemically at the end of branches called dendrites.
“Dendrites are central to understanding the brain because they are at the core of what determines the computational power of single neurons,” Walter Beckwith, Humboldt University neuroscientist Matthew Larkum, told the American Association for the Advancement of Science in January 2020.
Dendrites are the traffic lights of our nervous system. If an action potential is important enough, it can travel to other nerves, which can block or pass the message.
This is the logical basis of our brain – voltage ripples that can be communicated collectively in two forms: either a AND message (if x AND y are activated, the message is transmitted); or one OR message (if x OR y is activated, the message is transmitted).
Certainly, nowhere is this more complex than in the dense, wrinkled exterior of the human central nervous system; the cerebral cortex. The second and third deepest layers are especially thick, filled with branches that perform higher-order functions that we associate with sensation, thought, and motor control.
It was tissue from these layers that the researchers took a closer look at, attaching the cells to a device called a somatodendritic clamp to send action potentials up and down each neuron, recording their signals.
“There was a ‘eureka’ moment when we first saw dendritic action potentials,” Larkum said.
To ensure that any findings were not unique to people with epilepsy, they double-checked their results on a small portion of samples taken from brain tumors.
While the team had performed similar experiments in mice, the types of signals they observed buzzing through human cells were very different.
More importantly, when they dosed the cells with a sodium channel blocker called tetrodotoxin, they again found a signal. Only by blocking the calcium did everyone calm down.
The finding of a calcium-mediated action potential is quite interesting. But modeling how this sensitive new type of signal worked in the cortex revealed a surprise.
Apart from logic AND AND OR-type functions, these individual neurons can act as ‘exclusive’ OR (XOR) intersections, which allow a signal only when another signal is evaluated in a certain way.
“Traditionally, XOR the operation is thought to require a network solution,” the researchers wrote.
More work needs to be done to see how dCaAPs behave across whole neurons and in a living system. Not to mention whether it’s a human thing, or whether similar mechanisms have evolved elsewhere in the animal kingdom.
Technology is also looking to our nervous system for inspiration on how to develop better devices; Knowing that our individual cells have a few more tricks up their sleeves could lead to new ways to network transistors.
Exactly how this new logical tool squeezed into a single nerve cell translates into higher functions is a question for future researchers to answer.
This research was published in science.
A version of this article was originally published in January 2020.