Unique samples of brain tissue from living volunteers

Signal transmission by neurons

Scientists from Massachusetts Institute of Technology (MIT) took the opportunity to get a sample of excitatory neurons the size of a nail from the depths of the brain of volunteers undergoing surgical treatment of epilepsy.

This tissue was obtained from the anterior temporal lobe, capable of coping with the loss of several neurons, so patients did not feel it. But by doing so, the researchers received the type of tissue needed to observe how human nerves carry electrochemical messages over long distances.
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It is no secret that rats have a rather small brain with a relatively thin outer cortex, despite the fact that they are smart. Nevertheless, the organization of this thin outer layer is similar to how our brain works, which, in turn, raises questions about how our neurons cope with sending signals over long distances.

Stretched distribution of ion channels in human neurons

A standard neuron usually looks like a tree without leaves. Branches – dendrites – collect signals from other cells and transmit them through the cell body along a long thin proboscis – axon. Such transmissions are carried out by charged particles interacting with the neuron membrane through ion channels, producing voltage ripples along the entire length of the cell. However, these branches are more than channels for signals: they actively “pull” messages, playing a key role in the processing of portable information.

In a sense, dendrites can be referred to as transistors, amplifying some signals and blocking others. Scientists have concluded that in fact they may be even more involved in the processing of information by the nervous system. At least in humans.

“It’s not just that we are smart because we have more neurons and a larger cortex,” says lead researcher Mark Harnett. “In general, neurons behave quite differently.”

After extracting samples of neurons from the depths of the brain of volunteers, the researchers placed them in an environment similar to a cerebrospinal fluid, so that they remained alive for a day or so, while scientists figured out how signals travel along cells.

It turned out that these signals weaken in human neurons more strongly than in the same cells taken from mice. Nevertheless, both types of cells have the same number of ion channels in their membranes, which are just slightly wider in our neurons. Models developed by researchers suggest that this may be the reason for the difference in signals.

“In human neurons, a large compartmentalization occurs, which, in turn, allows them to be more independent, potentially leading to increased computational abilities of one neuron,” says Harnett.
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Whether this architecture can explain the difference in how our species process information remains to be seen. Harnett is sure that such a hypothesis should not be written off.