New Delhi, India

In a new study, the researchers have observed that the grey matter of the brain is probably shrinking by 80 per cent during pregnancy and creating "permanent etchings". 

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The researchers made the discovery when a pregnant neuroscientist went through two dozen brain scans during her pregnancy phase and then for the next two years postpartum. 

Grey matter is one kind of tissue present in the brain and spinal cord (central nervous system) which is important for humans to function normally. 

After the pregnancy came to an end, it was observed that the woman was able to regain some grey matter. The grey matter regained included the cell bodies of neurons and the connections present between them.

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Co-senior author of the study and associate professor of psychological and brain sciences at the University of California, Santa Barbara (UCSB) Emily Jacobs said that the grey-matter volume in the affected brain areas of pregnant women decreased by 4 per cent on average. 

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"That's similar to the amount of reduction in puberty," said Jacobs, while speaking at a news conference on Thursday (Sep 12). 

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During puberty, there is a hormone surge which comes with a decrease in grey matter volume as the excess tissue in the brain is pruned so that it can function more efficiently. 

Jacobs stated that something similar may have been occurring in pregnancy. 

Pregnancy may be changing brain's fine-tuning forever: Jacobs 

"Sometimes people bristle when they hear that grey-matter volume decreases during pregnancy — like, 'That can't be a good thing,'" she explained. 

However, "this change probably reflects the fine-tuning of neural circuits, not unlike the cortical thinning that happens during puberty," she added.

Jacobs suggested that there is a possibility that the brain's fine-tuning changes forever. 

"Many of these changes seem to be what you might think of as permanent etchings in the brain," she said.

However, the other changes observed in the study were temporary. 

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In the first and second trimesters, the insulated wiring between neurons and white matter turned more robust.

"We think of it as like a tube or like a straw," said Liz Chrastil, who is an associate professor of neurobiology and behaviour at the University of California, Irvine and senior co-author of the study, at the press conference. 

When the white matter turned robust, water flowed straight without any diversion or pooling. 

However, in the scans, the white matter was later seen returning to baseline after birth.

(With inputs from agencies)