London, Jan 13 (IANS): Long thought to be "junk DNA" of no real use, millions of years old inherited viruses actually play an important role in making the human brain dynamic and multifaceted in its functions, says a study.

These endogenous retroviruses that constitute around five percent of our DNA were earlier thought to be just a side-effect of our evolutionary journey.

Retroviruses seem to play a central role in the basic functions of the brain, more specifically in the regulation of which genes are to be expressed and when.

"We have been able to observe that these viruses are activated specifically in the brain cells and have an important regulatory role," said head of the research team Johan Jakobsson from Lund University in Sweden.

"We believe that the role of retroviruses can contribute to explaining why brain cells in particular are so dynamic and multifaceted in their function," Jakobsson added.

The reason the viruses are activated specifically in the brain is probably due to the fact that tumours cannot form in nerve cells, unlike in other tissues.

The findings based on studies of neural stem cells show that these cells use a particular molecular mechanism to control the activation processes of the retroviruses.

The results open up potential for new research paths concerning brain diseases linked to genetic factors such as neurodegenerative diseases, psychiatric illness and brain tumours, the researchers pointed out.

The study appeared in the journal Cell Reports.