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Watching a comedy show with Heather Berlin, a neuroscientist at Mount Sinai Hospital, must be a strange experience. You (and everyone else in the room) are focused on the jokes; Berlin, on the other hand, is mostly curious about the brain responsible for creating those jokes.

In an ongoing study, Berlin is using brain scanners to peer into the minds of rappers, to see what happens when the musicians are freestyling as compared to performing memorized material, similar to studies other researchers have done, with similar results, on improvisational jazz musicians. Next, she’d like to study the same thing on professional comedians — ideally, those who are both skilled comic performers and improvisers. “We want to add in the comedy group to see if there is actually some kind of neural signature of spontaneous creativity — something that looks the same, across different disciplines,” she said.

During our conversation, I asked Berlin if any comedians came to mind who were particularly good at this kind of spontaneous creativity, and she mentioned Jon Stewart. Here are a few more things Berlin had to say, both about Stewart and what’s likely going on inside the mind of a comedian:

On Stewart:

“I recently saw him in person, Jon Stewart. He is just brilliant at being in the moment and putting together separate ideas — he would take things that had occurred earlier in the night and then weave them together with other things that were happening in the moment. And you knew it couldn’t have been prepared in advance.”

On divergent thinking:

Quick-witted would be the layman way to put it; he’ll be interviewing someone on The Daily Show, and he’s just very quick, very quick at making these unexpected connections. But the term we would use for that is divergent thinking — that is, making novel connections between things that other people don’t put together, and finding the humor in that. You could also think of it as just “thinking outside the box.”

[Researchers] sometimes try to quantify this with tests — basically, you give someone something like a paperclip, and you tell them, Now I want you to list all the possible uses out of this paperclip. And so divergent thinking is coming up with some really amazing, crazy, creative things to use that simple paperclip for. So it’s novelty; it’s making these kinds of novel associations between ideas.

And the difference is, it’s not that they’re so far off that these things don’t even make sense. But it’s about being able to think outside the box, but still be in the realm of reality, not crossing over the line where it becomes so obtuse it doesn’t make any sense.

On improvising comedy:

So there are two different types of creativity. Well — there are many different types of creativity, but the way we’re looking at it, you know, there’s the very deliberate kind, when you sit down and go, I’m going to write this comedy routine. And you are creating, it’s just not spontaneous; you’re thinking, you’re editing, you’re going back, you’re reworking. What we’re more interested in is this in-the-moment, time-pressured kind of improvisation, where you have no time to go back and revise.

There have been studies on this type of thing before: two small studies, one with a small group of rappers and another with a small group of jazz musicians. And these gave us a basic idea of what’s happening inside the brain when you’re in this spontaneous, improvisational state — a part of the brain that has to do with internal generation of new, stimulus-independent ideas, activity in that area is turned up. It’s called the medial prefrontal cortex.

And then another part of your brain, it’s called the dorsal lateral prefrontal cortex, activity there is turned down. And that has to do with your feelings of being self-aware — like, monitoring, How am I doing? or What do people think of me? So that part is kind of your filter system. But because that’s turned down, what you have is the increase of this flow of information that comes from within, perhaps from your subconscious, and then a decrease of this filter, this self-critic. So that’s the state your brain is in when you’re able to make these novel, perhaps wacky, associations, that you maybe would not normally do when you’re not in a kind of improvising state of mind. We’re predicting, at least, that this will look similar in comedians’ brains.

On performing memorized comedy routines:

So with performing a memorized piece, obviously there’s going to be a lot more going on in the areas of the brain that are involved with memory: the hippocampus, but also the dorsal lateral prefrontal cortex. And the dorsal lateral prefrontal cortex, like I said, has to do with self-awareness, but it’s also involved with memory, and that kind of gets turned down when you’re doing improvisation. So it’s the opposite when you’re doing something you’ve memorized. You need to turn activation in that area up, so you have what we call working memory.

So with memorization, you’re not really being creative. I mean — you are, to a certain extent, because you have to invigorate the text with life, or how they act out the lines. But it’s a different creative process within the brain; you’re not having to create material from scratch. So the lack of self-monitoring or the internal generation of new ideas, that means the medial prefrontal cortex probably won’t be as high as when they’re doing a memorized piece, which makes sense.