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.
Interestingly, this discovery suggests that our brains may be more powerful computational units than we thought.
In 2020, researchers from institutes in Germany and Greece reported a mechanism in the brain's extracellular cortical cells that produces a new “gradient” signal of its own, a signal that can provide individual neurons with another way to carry out their logical functions.
By measuring electrical activity in sections of tissue removed during surgery on epilepsy patients and analyzing their structure using fluorescence microscopy, neurologists found that individual cells in the cortex use not only the usual sodium ions to “release,” but calcium as well.
This mixture of positively charged ions released waves of electrical voltages never seen before, referred to as calcium-mediated dendritic action potentials, or dCaAPs.
Brains – especially those of the human kind – are often compared to computers. The analogy has its limitations, but on some levels they perform tasks in similar ways.
They both use the power of electrical potential to perform different operations. In computers, this is a 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 molecules such as sodium, chloride, and potassium. This pulse of flowing ions is called a pulse Action potential.
Instead of transistors, neurons conduct these messages chemically at the end of branches called dendrites.
“Dendrites are fundamental to understanding the brain because they are essentially what determines the computational power of single neurons,” Humboldt University neuroscientist Matthew Larcom told Walter Beckwith At the American Association for the Advancement of Science in January 2020.
Dendrites are the traffic lights of our nervous system. If the action potential is large enough, it can be transmitted to other nerves, which can block or transmit the message.
These are the rationales of our brain – electrical voltage ripples that can be collectively communicated in two forms: either And message (if x And y is run, and the message is passed); or or message (if x or y is run, and the message is passed).
Arguably nowhere is this more complex than this in the dense, wrinkled outer part of the human central nervous system. Cerebral cortex. The second and third deeper layers are particularly thick, filled with branches that perform higher-level functions that we associate with sensation, thought, and motor control.
The researchers took a closer look at the tissue of these layers, and connected the cells to a device called a somatodendritic synapse to send active potentials up and down each neuron, recording its signals.
“There was a eureka moment when we first saw dendritic action potentials.” Larcom said.
To make sure any findings were not limited to people with epilepsy, they double-checked their results in a small number of samples taken from brain tumors.
While the team had conducted similar experiments On miceThe types of signals they observed buzzing through human cells were very different.
More importantly, when they injected the cells with a sodium channel blocker called tetrodotoxin, they were able to find a signal. Everything calmed down only by blocking calcium.
Finding calcium-mediated action potentials is interesting enough. But modeling the way this sensitive new type of signal works in the cerebral cortex has revealed a surprise.
In addition to logical And And orFunctions of the type, these individual neurons can act 'Exclusive' or (XOR) intersectionswhich only allows a signal when another signal is classified in a certain way.
“Traditionally, XOR “The process is believed to require a network solution.” The researchers wrote.
More work needs to be done to investigate how dCaAPs behave across whole neurons and in the living system. Not to mention if it concerns humans, or if similar mechanisms have evolved elsewhere in the animal kingdom.
Technology also looks to our nervous system for inspiration on how to develop better devices; Knowing that our individual cells have a few extra tricks up their sleeve could lead to new ways of connecting transistors to networks.
How this new reasoning tool confined to a single neuron translates into higher functions is a question that future researchers must answer.
This research was published in Sciences.
A version of this article was originally published in January 2020.
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