Well, those nostalgic ads work because they can not only make you remember the past, but can totally plant fake memories in your mind. The reason your grandpa remembers the 1950s as nothing but friendly neighbors and soda fountains is because ads and TV shows have been hammering his brain with those images for five straight decades.
Ah, the atomic age was the best!
Science has proven it; we described once before an experiment in which scientists were able to convince a bunch of people that they had met Bugs Bunny at Disneyland as children, just by describing the event to them. Participants were suddenly able to "remember" all the details, despite the fact that there has never been a Bugs Bunny at Disneyland, not unless Bugs got very lost (he's not a Disney character, for those of you who haven't caught up).
Advertising works the same way. Researchers did another study where they had a group of people watch a series of advertisements that described the experience of eating a popcorn product that the scientists just made up. Half of the participants were then fed this so-called brand of popcorn (which obviously didn't exist and was hopefully called Falsepop). The rest had to make do with cucumber sandwiches or whatever scientists usually serve for lunch.
When grilled about the experience just one week later, those who had seen the most vivid commercials were just as likely to remember actually having eaten the popcorn, whether they actually did or not. Think about that for a moment -- whether or not they actually ate the popcorn was not as important as how convincingly some advertising executive told them they had. And this wasn't months or years later -- it was seven freaking days.
The experiment was testing a theory of memory known as reconsolidation -- in short, the idea that our memories are not fixed and static, but can be altered and updated based on what our brain thinks is helpful new information. If you vaguely remember that your first grade teacher's hair was black and somebody shows you a photo proving it was brown, you will actually update your memories to remember it as brown ... even if the photo is a fake. We didn't just pull that example out of our asses -- a simple Photoshopped image was enough to convince test subjects they had taken a hot air balloon ride as kids, even though they'd never set foot in one.
"And that's how your mother died."