A new scientific study suggests that human brains make more neural connections during development, a phenomenon that leads to growing brains and differentiates us from Neanderthals.
Scientists have always pondered what makes humans a special species with some suggesting it’s because of the dramatic increases in the size and density of our brains during our development.
Until recently, almost no research has weighed in on whether we produce similar amounts of neurons to our closest cousins, the Neanderthals, although several studies have shown that humans boast a similar sized brain to Neanderthals.
However, according to a new finding in science, researchers identified a variation in one of the proteins in our brains that bolsters our brain progenitor cell counts.
The finding indicated that humans make more neurons during development than the Neanderthals did during theirs around 130,000 to 40,000 years ago.
Our increased neural production which occurs primarily in the neocortex draws scientists closer to understanding why the human species is so distinct from the rest.
Proteins distinguish between brain sizes of humans and Neanderthals
Although modern humans and Neanderthals have comparably sized brains and strikingly similar neocortexes, scientists are considering variations in the proteins in the brains to solve this mystery.
Neocortexes are the large areas of the brain that command complex functions such as sensory perception, attention, and memory. Hence, whether similar brain size implies a similar production of neurons remains a mystery.
Specifically, scientists are focusing on the protein TKTL1, which is found in the frontal lobes of the neocortexes of both modern humans and Neanderthals with only a single variation in their sequences of amino acid building blocks.
The TKTL1 protein contains an occurrence of arginine in a particular spot of its modern human sequence and lysine in the same spot of its Neanderthal sequence. This is the only difference between the two.
A slight variation in the amino acid sequence of the protein leads to a substantial increase in the number of basal radial glial cells present in the frontal lobe in the modern human brain.
Researchers further noted that because these cells are in charge of producing new neurons, their increase, in turn, yields a much greater number of neural cells in the brains of modern humans.
Experiment on mice brains yielded initial findings
Initial findings, although from an improbable source, involved conducting a series of experiments on mouse embryos. Researchers introduced two versions of the TKTL1 protein into the frontal lobes of embryonic mice brains.
They measured the resulting amount of basal radial glial progenitor cells in the neocortexes of the mice and noted that the cells increased with the modern human variant of the protein, thus resulting in higher production of neurons.
The team of researchers then tested the two variants on human brain organoids, artificial tissues created from stem cells to mimic the human brain, in the hope that this would further solidify findings.
They then substituted the modern human variant with the Neanderthal variant to see whether the switch would impact the human brain by using the artificial tissues.
In a press release, Anneline Pinson, a study author and a researcher at the Max Planck Institute of Molecular Cell Biology and Genetics noted that Neanderthal-type of amino acids in TKTL1 produce fewer basal radial glial cells.
“We found that with the Neanderthal-type of amino acid in TKTL1, fewer basal radial glial cells were produced than with the modern human-type and, as a consequence, also fewer neurons,” Pinson said.
“This shows us that even though we do not know how many neurons the Neanderthal brain had, we can assume that modern humans have more neurons in the frontal lobe of the brain, where TKTL1 activity is highest than Neanderthals.” she added.
These findings solidly reveal one of the main differences between the brains of modern humans and the brains of Neanderthals although, according to the team, it also serves a broader purpose, potentially pointing to the uniqueness of our species.
In conclusion, Wieland Huttner, a study supervisor and a researcher at the Max Planck Institute of Molecular Cell Biology and Genetics also said, “It is tempting to speculate that this promoted modern human cognitive abilities associated with the frontal lobe.”