Numerous deep ridges and furrows make the human brain look much like a walnut.
The wrinkly aspect is very recognizable but as you may or may not be aware, some brains are wrinklier than others, although the reason hasn’t always been clear.
The folding that happens on the outermost layer of the brain is a result of the squishy organ being squeezed inside the skull and on that surface is where thinking, memory, reasoning and learning take place.
In other words, the folding, also known as gyrification, is really important for brain function and circuitry and it’s believed to be the reason why human beings have greater cognitive abilities than other intelligent animals such as elephants and apes, which have not as many folds.
All that being said, a research team seems to have finally figured out why some brains are more fold-rich than others, even among humans.
This condition is known as polymicrogyria (PMG) and affects normal brain development.
Polymicrogyria involves too many gyri piled on top of one another which leads to an unusually thick cortex and a number of different problems including intellectual disability, neurodevelopmental delay, epileptic seizures and speech difficulties.
One of the scientists behind this study, neuroscientist Joseph Gleeson, explains that “Until recently, most hospitals treating patients with this condition did not test for genetic causes.”
Polymicrogyria can manifest in a variety of ways, with widespread or localized cortical thickening that shown up on brain scans.
This condition has been linked to mutations in 30 genes and counting but the way in which these genetic errors, whether by themselves or together, cause the brain tissue to overfold is still a mystery.
Not to mention that many of the cases do not have an identifiable genetic cause at this point.
The theory is that it is associated with the late cortical brain cell migration in early development.
In order to investigate this further, Gleeson worked with researchers from the Human Genetics and Genome Research Institute in Cairo.
Together, they investigated a database containing almost 10,000 Middle East families, affected by any type of pediatric brain disease.
This way, they found 4 families with an almost identical form of PMG, all presenting mutations in one gene that encodes a protein clinging to the surface of cells referred to as 161B (TMEM161B).
However, it was still not clear what it did.
In the experiments that followed, Gleeson and the rest of the team proved that TMEM161B is present in most fetal brain cell types but that from an evolutionary standpoint, it first appeared in sponges, which lack a brain.
This important detail really confused the team of scientists, including Gleeson and the lead author, another neuroscientist by the name of Lu Wang, who wondered if the protein could affect cortical folding indirectly by getting involved with some basic cellular properties shaping complex tissues.
Wang, noted that “Once we identified TMEM161B as the cause, we set out to understand how excessive folding occurs.”
As it turns out, in the absence of their internal scaffold, radial glial fibers are unable to scaffold other cells as they try to position themselves properly in the developing brain.
Of course, it’s worth mentioning that this study is still rather small and further research is needed to learn more.
However, Gleeson is rather hopeful, saying that “We hope physicians and scientists can expand upon our results to improve diagnosis and care of patients with brain disease.”