This is MORNING EDITION from NPR News. Good morning, I'm David Greene.

 

And I'm Renee Montagne.

 

In Your Health today: The connection between depression and dementia.

 

GREENE: But first, freshmen are heading to college this fall and about now they might be getting their roommate assignments. Some colleges allow students to pick their roommates, others assign roommates to students. And there is some new information about the effects that college roommates might have on each other.

 

NPR's social science correspondent Shankar Vedantam regularly comes into to discuss research he finds. And he is in the studios with me. Hey, Shankar.

 

SHANKAR VEDANTAM, BYLINE: Hi, David.

 

GREENE: So I'm thinking about my college roommates and the influences they might have had on me.

 

(LAUGHTER)

 

GREENE: I mean am I going to like what you're about to tell us?

 

VEDANTAM: So it turns out that your college roommates actually have a pretty big effect on your mental health. And to understand what that effect is, what you need to know is that researchers have found that the risk of depression is connected to something called your cognitive style.

 

GREENE: Cognitive style, is that just sort of the way we think about things?

 

VEDANTAM: Exactly, so bad things happen to all of us but we don't all think about those bad things in exactly the same way. I spoke with psychologist Gerry Haeffel, he's at the University of Notre Dame, and he gave me an example. Here he is.

 

GERALD HAEFFEL: Two people both lose their jobs. The question is why is it that one person becomes depressed and another one doesn't? Some people are people are going to think that losing their job means that they're a failure and they're going to brood about their negative mood. And that person is at risk for depression.

 

GREENE: OK, so we have two people who might be responding to the same problem. I'm guessing that the person who kind of just brushes it aside might be less likely to get depressed, the person who kind of broods about it is more likely to get depressed.

 

VEDANTAM: Yeah exactly, so if you're a student you don't think that failing one exam is the same thing as being a failure. You know, you distract yourself, you go out and you tell yourself I'm going to bounce back. I'll start...

 

GREENE: You get over it.

 

VEDANTAM: Yeah, exactly. So here's the last: What happens if you suddenly stop spending time with somebody who has a very different cognitive style than you? Now, when students show up at Notre Dame, they are assigned roommates. The students to get to pick who they are roommates are - it's fairly random. Right? So regularly, people who have a positive attitude are going to get paired up with someone who has a negative attitude.

 

And what Haeffel found is that in just three months, roommates started to infect one another with their cognitive style. Here he is again.

 

HAEFFEL: What we found is that these thinking styles were contagious. If you came to college and you had a roommate who had a very negative thinking style, your own thinking style became more negative.

 

GREENE: OK, I don't want to oversimplify it. But I mean are we saying that if we come to college in a good mood, and we end up kind of feeling depressed a few months later, it's all our roommates' fault?

 

(LAUGHTER)

 

VEDANTAM: Well, on average that is sort of what Haeffel is saying, that having a negative person around you a lot of the time has an effect on you. But it's also important to remember, David, that this actually works both ways. So it's true that the brooders made cheerful kids more, you know, broody. But it's also true that the cheerful kids made the brooders more cheerful. So now, instead of blaming themselves when something went wrong, the brooders started saying, Well, you know, it's just the circumstances and I'll bounce back - I'll start doing better.

 

So it's almost as if the thinking styles of the two roommates were converging. Right? Haeffel is a depression researcher. And what he finds is that six months after you start spending lots of time with somebody with a more negative attitude, your risk for depression significantly rises.

 

GREENE: Let's broaden this out, if we can, and get some perspective. I mean if we take this beyond college, how important is it that we find people who are upbeat...

 

(LAUGHTER)

 

GREENE: ...you know, to spend time with to make sure that we don't get depressed?

 

VEDANTAM: This is why I like spending time around you, David, because you're always cheerful.

 

(LAUGHTER)

 

GREENE: Nice of you.

 

VEDANTAM: But, you know, the truth is in life we can't always surround ourselves with cheerful people. Right? People are going to come in all shapes and sizes. The big take away for me from Haeffel's study, is that these Cognitive Styles are actually quite malleable. It used to be that we thought that the styles were fairly fixed. You know, once your brooder you're always going to be a brooder. Or once your cheerful person, you always stay at cheerful person.

 

What this experiment is showing us is that our peers and networks have a really powerful effect in shaping us. When we start spending time with somebody who is of very different temperament, it's the psychological equivalent of essentially landing in a new country. And so, our natural cognitive style - this mental language that we've always spoken - doesn't work anymore in this new country. And you have to start learning this new language.

 

And so, the take away for me is with effort in time we can all change our cognitive styles.

 

GREENE: It's an upbeat ending to this chat.

 

VEDANTAM: I think so.

 

GREENE: It's been great sharing a room with you you've been a wonderful influence, Shankar.

 

(LAUGHTER)

 

GREENE: Thanks a lot.

 

VEDANTAM: Thanks, David.

 

GREENE: That's NPR's Shankar Vedantam and you can follow him on Twitter @hiddenbrain.