Human intelligence is high not only because the cerebral cortex is large, but also because 'the behavior of neurons is fundamentally different'

by TheDigitalArtist

The explanation that "Because human cerebral cortex is large for human reasons" is often done, but in a study by Massachusetts Institute of Technology (MIT) Mark Harnett et al., In addition to the size of the cerebral cortex, "The behavior of neurons in the first place It is revealed that there exists a reason that it is different from other animals.

Electrical properties of dendrites help explain our brain's unique computing power | MIT News
http://news.mit.edu/2018/dendrites-explain-brains-computing-power-1018

Dendrites of neurons serve as transistors in computers. A transistor is like a switch for passing electricity, and by giving the correct voltage, it conveys the information of "1" and "O" necessary for logical operation of the program.

What is the "transistor" in the computer doing? - GIGAZINE

The dendrite plays a role of transmitting the signal received from other neurons to the body of the neuron. This electric signal causes an action potential to be transmitted to other neurons, so that huge networks composed of neurons exchange information and thoughts and behaviors are born.

Previous studies have shown that the signal strength transmitted by dendrites depends on how far the information has traveled. In other words, the stimulation of the signal received from the neighboring neuron is strong, while the signal flowing from the distant neuron weakens.

The characteristic of the human brain is that the cerebral cortex is thick. Rat cerebral cortex is about 30% of the whole brain, but human cerebral cortex occupies about 75%. And because the cerebral cortex is thick, the dendrites that convey information are also longer than other animals.

The human cerebral cortex is 2-3 times as thick as rats, but its structure is made from the same six layers of neurons as other mammals. The dendrites of the fifth layer of neurons are long enough to reach the neurons of the first layer, which is believed to have become longer to deliver electric signals at the stage of the evolution of the brain.

by geralt

MIT's research team investigated how dendrite length relates to the nature of the electrical signal by comparing it with the mouse. Experiments were conducted in a way that brain tissues were collected from epilepsy patients who had resected the anterior temporal lobe by brain surgery and used for experiments. In addition, some of the brains used for experiments did not suffer from diseases, and that they functioned normally. Although it was part related to language and visual information processing that was excised, it is said that the patient was able to perform those functions normally even after resection.

After being resected, the tissue was placed in solution simulating cerebrospinal fluid and given oxygen, it continued to function normally for 48 hours. In the meantime, researchers measured how the neuronal dendrites, called pyramidal cells , measure electrical signals using the patch clamp method .

The result turned out to be that "the electric signal transmitted from the 1st layer neuron to the 5th layer neuron" becomes weaker than that of rats. In addition, both the dendrites of rats and human dendrites have the same number of ion channels that control the current, but human beings have also been shown that their densities are low for long dendrites. It seems that each neuron is compartmentalized, and each computing power is increasing. By creating a biophysical model, researchers show that the difference in density of ion channels is responsible for the difference in strength of electrical activity.

"The only thing that is wise is that there are many neurons and the cerebral cortex is large, not the only reason is not the root, the behavior of neurons is fundamentally different," Harnett says.

by geralt

However, we do not yet know how these differences are related to human brain power. Harnett's hypothesis states: "Differences in density allow more parts of human dendrites to be involved in the input signal, so that each neuron can perform more complex processing on the information It is said to be what it is.

There are various other differences in neurons of humans and other animals. In the future research, Mr. Harnett further investigated the accuracy of the impact of the electrical signal transmitted by the neuron, and explored how the unique characteristics of human beings will exert the power of computing by involving them We are doing it.