Researchers find myelin development differences between chimps and humans

September 25, 2012 by Bob Yirka report
Myelin sheath. Credit: Wikipedia.

(Medical Xpress)—A mixed background group of US researchers has found in studying chimpanzee brains, that development of myelin, the fatty sheath that covers the connections between nerve cells, occurs at a different rate than for humans, and as they write in their paper published in the Proceedings of the National Academy of Sciences, the differences might account for the greater instance of mental disorders in people than in both chimpanzees and other primates, such as macaques.

Myelin is a fatty coating that covers axons, the connections between , rather like the plastic sheathing that covers household electrical wiring. Its purpose is to help control the flow of between neurons. Many disorders come about in people who experience demyelination, or the loss of myelin, most notoriously, multiple sclerosis. More research recent has suggested that problems with myelin might also be at the root of some , such as schizophrenia, bi-polar disorder or . This new study bolsters such thinking as the team has found that myelin development in human beings is markedly different than it is for chimpanzees.

Prior research has shown that myelin development in other primates, such as macaques occurs at a different rate than for humans, but until now, a similar study on chimpanzees had not been undertaken due to the difficulty in obtaining brain samples from them. In this new effort, the team was able to examine the brains of 20 chimps that had died due to non-research related causes and in so doing they found that myelin development occurred at very nearly the same rate as for other primates, which indicates that there is a clear difference between the rates of development in humans versus most, if not all, other primates.

are born with almost no myelin at all. Shortly after birth, they have a spurt of sorts, with a lot of developing occurring and continuing on slowly thereafter for some thirty years. Other primates, in contrast, begin developing myelin while still in the womb and it keeps up just until the animal reaches sexual maturity, at which point, it stops completely.

The researchers speculate that the differences in myelin development may explain some of the unique mental abilities of people, as being born with little to no myelin, allows for more openness to learning from the environment as opposed to relying on information passed on through genes. They also suggest those same differences might be putting people at more of a risk of developing mental illness though, as the possibility of something going wrong during the process grows greater over longer periods of time.

Explore further: Hope for infant brain injuries like cerebral palsy as well as multiple sclerosis

More information: Prolonged myelination in human neocortical evolution, PNAS, Published online before print September 24, 2012, doi: 10.1073/pnas.1117943109

Nerve myelination facilitates saltatory action potential conduction and exhibits spatiotemporal variation during development associated with the acquisition of behavioral and cognitive maturity. Although human cognitive development is unique, it is not known whether the ontogenetic progression of myelination in the human neocortex is evolutionarily exceptional. In this study, we quantified myelinated axon fiber length density and the expression of myelin-related proteins throughout postnatal life in the somatosensory (areas 3b/3a/1/2), motor (area 4), frontopolar (prefrontal area 10), and visual (areas 17/18) neocortex of chimpanzees (N = 20) and humans (N = 33). Our examination revealed that neocortical myelination is developmentally protracted in humans compared with chimpanzees. In chimpanzees, the density of myelinated axons increased steadily until adult-like levels were achieved at approximately the time of sexual maturity. In contrast, humans displayed slower myelination during childhood, characterized by a delayed period of maturation that extended beyond late adolescence. This comparative research contributes evidence crucial to understanding the evolution of human cognition and behavior, which arises from the unfolding of nervous system development within the context of an enriched cultural environment. Perturbations of normal developmental processes and the decreased expression of myelin-related molecules have been related to psychiatric disorders such as schizophrenia. Thus, these species differences suggest that the human-specific shift in the timing of cortical maturation during adolescence may have implications for vulnerability to certain psychiatric disorders.

Press release

Related Stories

Recommended for you

Umbilical cells help eye's neurons connect

November 24, 2015

Cells isolated from human umbilical cord tissue have been shown to produce molecules that help retinal neurons from the eyes of rats grow, connect and survive, according to Duke University researchers working with Janssen ...

Brain connections predict how well you can pay attention

November 24, 2015

During a 1959 television appearance, Jack Kerouac was asked how long it took him to write his novel On The Road. His response – three weeks – amazed the interviewer and ignited an enduring myth that the book was composed ...

No cable spaghetti in the brain

November 24, 2015

Our brain is a mysterious machine. Billions of nerve cells are connected such that they store information as efficiently as books are stored in a well-organized library. To this date, many details remain unclear, for instance ...

Neurons encoding hand shapes identified in human brain

November 23, 2015

Neural prosthetic devices, which include small electrode arrays implanted in the brain, can allow paralyzed patients to control the movement of a robotic limb, whether that limb is attached to the individual or not. In May ...

Wireless sensor enables study of traumatic brain injury

November 23, 2015

A new system that uses a wireless implant has been shown to record for the first time how brain tissue deforms when subjected to the kind of shock that causes blast-induced trauma commonly seen in combat veterans.

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Sep 25, 2012
I wonder if the real reason for the absence of myelin in the brains of human newborns is to allow the fetus's brain to be a little smaller and thus make childbirth a little easier. (Childbirth is exceptionally difficult for humans because walking on two legs necessitates a narrower birth canal, and because humans have relatively large skulls.) Shortly after birth humans have a spurt of myelin production which is accompanied by growth in their skulls.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.