Scientific investigators at MIT’s McGovern Institute conducted what Mark Harnett called his “Holy Grail” of experiments using live human brain tissue. While scientists have long been able to study the neurons of rodents, they finally were able to compare them with live human brain cells and analyze what makes them different. As it turns out, they discovered a tiny but incredibly important difference that could turn each human brain cell into a tiny mini-computer compared to in rodents or other mammals.
It’s the “first recording of electrical activity in human cells at a super-fine level of detail,” according to NewScientist.
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To obtain the live brain tissue, the researchers collaborated with other research-oriented neurosurgeons who were able to provide samples without harming patients. Researchers at MGH provided the brain tissue from patients who required surgery for intractable epilepsy. Abnormal regions of the patient’s brains were removed, but to do that, they had to remove small parts of healthy tissue in the overlying anterior temporal lobe. But don’t worry, the patients function normally since it’s not critical for any specific function in the brain.
The brain tissue, which would otherwise have been discarded, was saved in a culture of artificial cerebral spinal fluid. That way, the experiments could take place on the live neurons for a full 48 hours. It also meant the researchers had to put all other plans on hold when the tissue became available.
The scientists look at thin slices of brain tissue under a microscope.
“Under the microscope, there’s this sort of moment where we bring the brain slice into focus, and sometimes, there’s just nothing there. It’s just dead,” explained Harnett. “But other times, it’s just filled with live, fat, happy, juicy looking neurons.”
The researchers use incredibly tiny glass pipettes to gain access to the membrane of the cells. They can fill the neurons with dyes that reveal the structure. Using thin microscopic electrodes, they could study how the neurons reacted with each other. At first, they didn’t find what they expected to find, which would have been a key difference between the brain cells of rats and humans.
However, after the looked more closely at the parts of the neuron farthest away from the main trunk of the cell, called dendrites, they found a key difference not noticed before.
“[…] So the human neuron is sort of forming its own individual kinds of neural networks. It’s sort of a network inside a neuron.”
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If you picture the neuron as a tree with branches, those branches are much longer and thinner in humans. That’s partly because they have evolved to cover longer distances due to the much thicker brain of a human. Those thin and long branches, or dendrites, have fewer ion channels than found in rats. The ion channels are molecules that let electricity flow along the dendrite in the cell’s outer membrane. This might at first seem like a disadvantage, as the electrical signal becomes weaker traveling a long human dendrite than it does in a rat’s neuron.
However, that key difference has caused the human neurons to function more independently. Individual dendrites have more autonomous power to determine if the main neuron will eventually fire. On the other hand, a rat’s neurons are more likely to fire without a more involved process in the dendrites. Harnett hypothesized that this difference allows human brain cells to behave in much more complex ways. Even so, he says computations can occur at a much faster rate.
“Harnett’s hypothesis is that because of these differences, which allow more regions of a dendrite to influence the strength of an incoming signal, individual neurons can perform more complex computations on the information.”
There are an estimated 100 billion brain cells in a human, and now we think that each of those cells can operate as if it is an individual computer.
Now imagine all those billions of computers could come together and work for things that matter like turning around climate change, solving world hunger, preventing pollution, and creating a more peaceful, prosperous, and kind world.
See researcher Mark Harnett explain his findings in the video from McGovern Institute for Brain Research at MIT below:
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