The brilliance of Albert Einstein's brain may have been down to unusually well-connected left and right hemispheres, U.S. and Chinese researchers say.

Florida State University evolutionary anthropologist Dean Falk, using a technique developed by Weiwei Men of East China Normal University's Department of Physics, says the study was the first detailed look at Einstein's corpus callosum, the brain's largest bundle of fibers connecting the two cerebral hemispheres and facilitating interhemispheric communication.

"This study, more than any other to date, really gets at the 'inside' of Einstein's brain," Falk said in an FSU release Friday. "It provides new information that helps make sense of what is known about the surface of Einstein's brain."

Men's technique measures the varying thicknesses of subdivisions of the corpus callosum where nerves cross from one side of the brain to the other that indicate the number of nerves that cross and therefore how "connected" the two sides of the brain are in particular regions.

The technique permitted comparison of Einstein's brain measurements with those of two samples, one of 15 elderly men and one of 52 men Einstein's age in 1905, his so-called "miracle year" when he published four articles considered the foundation of modern physics, changing the world's conception of space, time, mass and energy.

Einstein had more extensive connections between certain parts of his cerebral hemispheres compared to both the younger and older control groups, the researchers said.

In an autopsy following Einstein's death in 1955, the autopsy surgeon removed the brain without the family's permission, with the thought future investigation might uncover the source of Einstein's intelligence.

Falk and Men worked from high-resolution photographs of the inside surfaces of the two halves of Einstein's brain published in 2012.