"If you use your cell phone a lot, it becomes part of you," Dr. William Barr, the chief of neuropsychology at the New York University School of Medicine, told ABCNews.com. "It's like wearing a tight sock all day. When you take it off, you still feel it there on your foot. If your cell phone is not there, you still feel like it is."
Our reliance on our cell phones may actually be "training" some of us to believe it is vibrating when it is not. In the case of cell phones, people are rewarded when they pick up their calls and read their incoming text messages, which causes them to pick up their cell phones more and more frequently.
"People are rewarded when they are able to detect low amplitude vibrations so they get better and better at responding," said Jon Kaas, a professor of psychiatry at Vanderbilt University. "It is very rewarding to get the message, so people are able to train their system to detect that signal."
As people repeat this behavior over and over again, connections between nerves in their brain become stronger and new ones are formed, which helps to make the behavior automatic.
And sometimes, as is the case with vibrating cell phones, the behavior becomes too automatic.
"People have gotten so good at detecting vibrations that they start responding to false positives -- they think something is there when it is not," Kaas said.
When it comes to the possible downsides of mobile device use, the side effects are not all in our heads. Our thumbs, it turns out, may also bear the brunt of our reliance on these devices.
The sores and blisters that some experience from too much texting and typing have earned monikers such as "BlackBerry thumb." And while the sore thumbs may seem like a new phenomenon, medical experts say there is a rational explanation for this modern-day nuisance.
"They are really repetitive stress injuries -- pain, numbness, discomfort in the base of the thumbs from overuse," Margot Miller, a physical therapist and president of the Occupational Health Section of the Orthopedic Section of the American Physical Therapy Association, told ABCNews.com.
These sorts of injuries, known as repetitive strain injuries or a repetitive motion disorders, are sometimes minor. But they can also lead to serious medical problems.
"I've seen a significant increase in the number of people with pain in their tendon regions in their thumbs and their fingers," Dr. Richard Brown, an orthopedic hand surgeon at the Scripps Memorial Hospital in La Jolla, Calif., said.
"I have to send them to the therapist or start them on medicine or put them in splints or, sometimes even operate."
Those with allergies to certain metals, such as nickel, may experience yet another side effect of exposure to their cell phones in the form of contact dermatitis.
In recent years, dermatologists have begun to see an increasing number of contact dermatitis patients who are allergic to these metal components in their cell phones.
"Some people are extremely nickel-sensitive," Dr. Lionel Bercovitch, a professor of dermatology at Brown Medical School, told Kirk Fernandes of ABC News OnCall.
Nickel is a metal that's used in a wide variety of products, including jewelry, belt buckles and watch bands. It's the most common cause of contact dermatitis in the developed world.
The symptoms of a nickel reaction range from mere redness to an obvious rash, or even blisters.