The joke that the next generation will evolve thumbs perfectly suited to texting on their smartphones has a grain of truth, it turns out; using a smartphone screen actually changes how our brains and thumbs work together, researchers say.

Over time, touchscreen use leads to greater brain activity when thumbs or other fingertips are touched, a study conducted by Swiss scientists found.

Arko Ghosh of the University of Zurich realized that smartphones represented an unexpected opportunity to investigate the everyday plasticity -- the changeability -- of the human brain as people are increasingly using their thumbs and fingertips in brand new ways.

And since smartphones maintain a record of their user's daily activities they provide a convenient source of data about those activities.

"I think first we must appreciate how common personal digital devices are and how densely people use them," Gosh says. "What this means for us neuroscientists is that the digital history we carry in our pockets has an enormous amount of information on how we use our fingertips (and more)."

To analyze finger and thumb use and its link to brain activity, Ghosh and his colleagues recorded EEG brain responses to touches on the thumb, index, and middle fingertips of touchscreen phone users.

They then compared that to brain activity in people who were still using old-school non-touchscreen mobile phones.

They found brain activity of smartphone users increased when any of the three fingertips were touched and in fact the level of the activity in the cortex region of the brains associated with the thumb and index fingertips was increased in direct proportion to the intensity of phone use.

That's strong evidence that repetitive finger and thumb movements over the surface of a smartphone screen reshapes sensory processing received from the hand that continually updates the brain's representation of the fingertips, the researchers report in the journal Current Biology.

"We propose that cortical sensory processing in the contemporary brain is continuously shaped by personal digital technology," they write.

While neuroscientists have conducted numerous studies on brain plasticity in expert groups for whom hand movement is important -- musicians and video gamers, for example -- smartphones have provided a new window into how daily life activities can shape the brains of all kinds of people, the researchers say.

"I was really surprised by the scale of the changes introduced by the use of smartphones," Gosh says.