Babies` brain growth reflects human evolution: Study

The growth of human brains between infancy and adulthood gives clues about human evolution.

Last Updated: Jul 13, 2010, 16:17 PM IST

Washington: Watching how human brains grow between infancy and adulthood is almost similar to watching evolution in action, says a new study.

Researchers at the Washington University found that the brain regions that expand the most during infancy and childhood are the same parts that expanded the most during
evolution as humans diverged from other primates.

It`s not an absolute one-to-one correlation, but the overlap is so striking that it`s hard to ignore, said David Van Essen, who led the study.

For their study, the researchers analysed brain scans of 12 full-term infants and compared those with scans from 12 healthy young adults aged between 18 and 24 years.

Data from the two groups were combined into a single atlas to quantify the differences between the infant and young-adult brains.

They found that the cerebral cortex -- the wrinkled area on the surface of the brain responsible for higher mental functions -- grows in an uneven fashion.

Every region expands as the brain matures, but the research showed one-quarter to one-third of the cortex expands approximately twice as much as other cortical areas as an
infant matures into a young adult, LiveScience reported.

According to the scientists, the findings revealed "evolution`s imprint on the human brain" because the rapidly developing parts of the brain are also those that differ most
when the human brain is compared to primates`.

"Through comparisons between humans and macaque monkeys, my lab previously showed that many of these high-growth regions are expanded in humans as a result of recent evolutionary changes that made the human brain much larger than that of any other primate," said Van Essen.

"The correlation isn`t perfect, but it`s much too good to put down to chance."

The high-growth regions are areas linked to advanced mental functions, such as language, reasoning and what Van Essen called "the abilities that make us uniquely human".

He speculated that the full physical growth of these regions may be delayed somewhat to allow them to be shaped by early life experiences.

The limitations on brain size imposed by the need to pass through the mother`s pelvis at birth might also force the brain to prioritise, said co-author Dr Terrie Inder, professor
of pediatrics at Washington University School of Medicine.

"Vision, for example, is a brain area that is important at birth so an infant can nurse and learn to recognise his or her parents," Inder said.

"Other areas of the brain, less important very early in life, may be the regions that see greater growth as the child matures."

Inder and colleagues are currently conducting similar scans of premature babies at birth and years later.
"This study and the data that we`re gathering now could provide us with very powerful tools for understanding what goes wrong structurally in a wide range of childhood
disorders, from the after effects of premature birth to conditions like autism, attention-deficit disorder or reading disabilities," Inder said.

The study is published in the Proceedings of the National Academy of Sciences.

PTI