But the researcher, Silvano Vinceti, said the portrait also represents a synthesis of Leonardo's scientific, artistic and philosophical beliefs. Because the artist worked on it at various intervals for many years, he was subjected to different influences and sources of inspiration, and the canvas is full of hidden symbolic meanings.

"The 'Mona Lisa' must be read at various levels, not just as a portrait," Vinceti said.

This is one of many theories that have circulated over the decades about the identity of "Mona Lisa" and the meaning for her famously enigmatic smile. Others have said the painting was a self-portrait in disguise, or the depiction of a Florentine merchant's wife — the latter drawing a consensus among scholars.

The world famous portrait is on display at the Louvre Museum in Paris.

The apprentice Gian Giacomo Caprotti, known as Salai, worked with Leonardo for