Its true! Learning something new can cause the same type of pleasure as some drugs and the addreneline rush of action. According to John Ratey, a psychiatrist with an expertise in attention deficit disorder, "It's like a dopamine squirt to be connected. It takes the same pathway as our drugs of abuse and pleasure."
"It's an addiction," he said, adding that some people cannot deal with down time or quiet moments. "Without it, we are in withdrawal."
So, Next time you spend hours online wandering the nodes and your spouse/girlfriend (HA!)/mom yells at you, just say "I need to get my fix!"

New York Times, The lure of data: is it addictive?