Author: Seven Jun
Human beings claim to be the spirit of all things, and the most spiritual is the head. But what is different about the human head from other animals? Aside from the fact that the human brain is larger than the body, the human brain doesn't know much about why it is so smart. However, more than 20 years ago, humans were finally able to come up with a "real hammer", which is a strangely shaped nerve cell.
Such cells are spindle cells.
Pyramidal neurons (left, the main unit of neural activity of the mammalian prefrontal cortex) and cellular spindle cells (right). | wikipedia
As the name suggests, spindle cells look like shuttles. Nearly 20 years of research have found that only humanoids, as well as a small number of "big-headed" intelligent animals, have this nerve cell. Although research is still ongoing, these nerve cells have been found to be related to self-awareness and "intuition" .
Figure | wikimedia
Most nerve cells are conical or star-shaped, filled with dendrites that receive signals from other nerve cells. But the spindle cells are very slender, with only one dendrite. Spindle cells are also very large, about 4 times the size of other nerve cells, and very rare, only about 1.25% of nerve cells in the human brain are spindle cells.
Spindle cells were first discovered in 1926 by the Austrian anatomist Constantin von Economo. But for a long time, this nerve cell has been eating ash in obscurity in the literature library and has not been taken seriously.
Later, in 1995, Patrick Hof, a neurologist at the Icahn School of Medicine in Mount Sinai in the United States, once again independently discovered spindle cells in the human brain. After searching the literature, he found that he was not the first person to make this discovery, so he later named the spindle cell Von Economo neuron.
In 1999, there were significant advances in the field of spindle cell research.
That year, John Allman, a neuroscientist at the California Institute of Technology, and his colleagues reported that all apes had spindle cells, but primates more distantly related to humans, such as lemurs and tarsiers, did not. This suggests that spindle cells are traits that evolved independently from the ancestors of all human families 10 to 15 million years ago.
A group photo of the extant humanoid ape. See the watermark in the lower right corner of the image source
Compared to other great apes, humans have a better number of spindle cells. For example, adults have about 80,000 spindle cells, only 16,000 gorillas, 2,000 bonobos, and only 1,800 chimpanzees. In addition, the spindle cells of humans and bonobos are larger than those of chimpanzees, gorillas, and orangutans.
Allman They also found for the first time that spindle cells appear in the anterior cingulate cortex of a human family.
The front buckle belt cortex (red) | wikipedia
The anterior cingulate cortex is an older part of the human brain, mainly responsible for automated functions such as heartbeat, blood pressure, and expression recognition. When a person's mood fluctuates, the anterior cingulate cortex reacts greatly.
In addition, spindle cells also appear in the bilateral frontal isola cortex. The bilateral frontal cortex is associated with spatial perception, self-awareness, and socially generated emotions such as guilt, empathy, embarrassment, and love.
Bilateral frontal cortex (green) | wikipedia
Coincidentally, when spindle cells appear, it is also the moment when humans produce the above "emotional intelligence".
Yes, the number of spindle cells is not set in stone. Humans are born with only 15% spindle cells, and the remaining 85% appear after the age of 4. According to Allman, the number of spindle cells began to surge when humans were 4 years old, and human moral feelings, guilt, and embarrassment also happened to appear during this period.
So, what exactly are the spindle cells that appear only in these two brain regions for?
Our understanding of spindle cells is still limited. In general, however, large nerve cells conduct very quickly. In 2015, Lucina Q. Uddin, a researcher at the University of Miami School of Medicine, pointed out in a review published in Nature Reviews Neuroscience that the main function of spindle cells is to transmit signals at high speeds from point to point, facilitating the brain to make "intuitive" responses.
Allman argues that spindle cells are a sign of the emergence of self-awareness.
If the appearance of spindle cells represents the beginning of self-consciousness of animals, then if the spindle cells are damaged, will there be a problem with people's self-consciousness?
It is true that some psychiatric disorders have been found to be associated with spindle cell abnormalities. For example, patients with frontotemporal dementia have fewer spindle cells than normal people.
In 2004, William Seeley, a medical researcher at the University of California, San Francisco, found that the brain regions of people with frontotemporal lobe dementia who had lost self-awareness were the anterior cingulate cortex and the bilateral frontal isola cortex. Autopsies showed that compared with healthy people, patients with frontotemporal lobe dementia had 74 percent fewer spindle cells in the anterior cingulate cortex, while other nerve cells were safe and sound.
Figure | pixabay
Typical symptoms of patients with frontotemporal dementia are a lack of empathy and self-awareness, and patients sometimes engage in antisocial behaviors such as robbery. In the study, another type of dementia, the anterior cingulate cortex of alzheimer's patients, did not change.
Other studies have found that the number of spindle cells in autistic patients and some people with suicidal mental illness is also different from that of ordinary people.
In short, spindle cells are likely to be associated with social, intuitive, self-aware, and empathetic abilities. Because of this, spindle cells were once seen as important anatomical evidence to distinguish between higher primates and other animals.
The discovery of spindle cells has undoubtedly added a new dimension to the study of consciousness and intelligence. More interestingly, in recent years, some intelligent animals with large heads have also been found to have spindle cells, including elephants, the largest animals on land, and whales, the largest animals in the ocean.
In 2009, Allman's team found that elephants also had spindle cells, but of the 1.3 million nerve cells in elephant brains, only 0.8 percent were spindle cells, fewer than humans.
In 2007, the above-mentioned Patrick Hof discovered that humpback whales, fin whales, sperm whales, and killer whales all have spindle cells. But in the brains of these marine mammals, spindle cells are found not only in the anterior cingulate cortex and bilateral frontal isolas, but also in the back of the brain; their spindle cells account for a close proportion of the whole brain than in humans.
Hof and colleagues believe that the rapid transmission of signals between these spindle cells allows the cetean to respond quickly to emotional cues in social interactions, and the discovery of nerve cells that were previously thought to exist only in the brains of humans and their primates can support the advanced cognitive abilities of the cetaceans, indicating that these marine mammals are likely to have the same empathy and ability to perceive the emotions of other whales as humans.
Killer whales that fish for birds with fish in zoos. Killer whales have spindle cells.
Of course, until the function of spindle cells is further studied, some people think that there is nothing special about it. For example, according to Terrence Deacon, an anthropologist at the University of California, Berkeley, spindle cells may be just a class of nerve cells produced in larger brains, while human intelligence may not lie in the type of nerve cells, but in the structure on a larger scale.
Nor is the controversy over dolphins and whales, as well as the spindle cells found in elephant brains, limited to academia. While whether non-human animals with spindle cells are self-aware, can perceive love and pain, and have "emotional intelligence" is an academic topic, they are also ethical topics. Is it reasonable to hunt, captive or enslave animals that also have spindle cells, such as killer whales and elephants?
Finally, if spindle cells are shown to be the figurative embodiment of self-awareness and empathy, and there are not only higher primates with spindle cells, then the question returns to the original point: What is man?
Humans have found that not only humans will be embarrassed, but it is humans who are embarrassed.
Cover source: wikimedia
bibliography
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[2] Hakeem, Atiya Y.; Chet. C. Sherwood; Christopher J. Bonar; Camilla Butti; Patrick R. Hof; John M. Allman (December 2009). "Von Economo Neurons in the Elephant Brain". The Anatomical Record. 292 (2): 242–248.
[3] Hof, Patrick R., and Estel Van der Gucht. "Structure of the cerebral cortex of the humpback whale, Megaptera novaeangliae (Cetacea, Mysticeti, Balaenopteridae)." The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology: Advances in Integrative Anatomy and Evolutionary Biology 290.1 (2007): 1-31.
[4] Uddin, Lucina Q. "Salience processing and insular cortical function and dysfunction." Nature reviews neuroscience 16.1 (2015): 55-61.
[5] Seeley, William W., et al. "Early frontotemporal dementia targets neurons unique to apes and humans." Annals of Neurology: Official Journal of the American Neurological Association and the Child Neurology Society 60.6 (2006): 660-667.
[6]www.smithsonianmag.com/science-nature/brain-cells-for-socializing-133855450/
[7]science.slc.edu/~jmarshall/courses/2007/fall/singularity/nytimes/humanity-may-be-in-wiring.pdf