If you're among the 50% of people who check email from bed when you should be sleeping, then you know: As a society, we are completely addicted to our email.
And you can chalk it up to dopamine -- the neurotransmitter that makes us keep doing stuff that feels rewarding. Back in the day, those were things like eating, or having a nice conversation.
But now, many psychologists believe that the brain can become addicted to other things, like the internet. That means getting unread email notifications can trigger the same dopamine path. So we repeatedly check it, hoping for the same reward.