Carl Zimmer: I want to start out by talking about how surprisingly bad our brains are. We assume that they perfectly record everything around us, but research shows that we can be blind to things that are staring us in the face. What does this discovery tell us?
Sam Wang: We might imagine that the visual part of our brain handles information the way a camera does, or perhaps our memory works the way a computer’s hard drive does. But that’s not the case.

When we process a visual scene, we are in the business of extracting salient features. We might be interested in finding a face in the scene or looking for objects. At the same time, we are in the business of throwing away information. Instead of getting all the pixels of a bottle of water I see, I might want to reduce it just to “bottle of water.” I might not be concerned about the fact that a particular bottle of water looks a little bit different from the other bottles. We toss away things that are not salient.

These shortcuts help us survive. They get us through the jungle. They get us to live another day. What they don’t get us is a little gigabyte hard drive of factual information.

Zimmer: Often it seems that we recall musical memories better than visual ones. Does that offer more clues into how the brain stores information?
Daniel Levitin: I think music can tell us a lot about the role that emotion plays in memories, the accuracy of memories, and the way in which knowledge can be encoded into memory.

When a song comes on the radio that you haven’t heard since high school, you’re right there with it. You’re singing along. You remember all the nuances. The big story of memory revealed by music is that you tend to remember those things that you care about or that you have some deep emotional connection with. It can be a positive emotion, it can be negative, but there appear to be neurochemical tags associated with memories that are highly emotional. Those are the ones that get most accurately recorded in your memory and the ones that are easiest to draw out.

Now, accuracy. What we’ve learned from musical memory is that it is astonishingly accurate. People can remember details and nuances of songs they know to such a degree that you can play them a 100-millisecond burst of a piece of music they know and they can name it from that. I’m talking about a tenth of a second—before the melody has a chance to evolve, before there’s any rhythm. If you alter a little bit of a well-known piece of music, people pick it up instantly. And if I were to ask you to sing your favorite pop song, the likelihood is that you would sing it at very near the right tempo and in very near the right key, even if you’re not a professional singer. It’s the nature of memory in general and musical memory in particular that it has this accuracy.

The third thing has to do with knowledge representation. There is something special about music that allows us to encode information. For tens of thousands of years before humans had writing, they still had important information they needed to preserve, to pass on to their children, to share. Anthropology has taught us that most of this information is encapsulated in song. I’m talking about survival information: which plants are poisonous and which aren’t, how you treat a wound so that it won’t become infected, don’t drink from that well over there. Our ancestors discovered that if they set the words to music they were easier to remember. The internal constraints of music—the meter, the accent structure—not to mention poetic elements like alliteration and rhyme, limit the possible words that will fit.

Almost every child learns the alphabet through a song. We learn the body parts. You put your right foot in, you put your right foot out, you shake it all about; you do the Hokey Pokey. That is what it’s all about.

Zimmer: We asked DISCOVER readers to submit questions, and we got a great one: “Where is consciousness in the brain?”
Michael Gazzaniga: The brain is a vastly parallel distributed system. There are specializations throughout the brain that carry out particular tasks. The consciousness trick is that any particular mental state you might be in is enabled by neural circuits specific to that state. That sounds fancy, so let me break it down into a clinical example.

For years I’ve studied patients who have had their brain hemispheres divided in an effort to control epilepsy. This results in people who can speak and talk and think out of the left hemisphere but who are now disconnected from the right. The right hemisphere does not speak, as a rule, and has very limited cognitive capacities. The overriding finding from studying these patients is that the left brain doesn’t seem to miss the right.

But after the surgery, if these patients are looking right at you, they can’t see the right half of your face. Yet they never mention it. They never see it as a problem. It never comes into their mind. So you realize that maybe the consciousness about that half of space is actually localized in the hemisphere that is now disconnected. It isn’t even a concept to the other hemisphere, the one that is doing the talking.

All of these circuits that are distributed throughout the brain allow for what we call conscious experience. I like to think of it as being like a pipe organ. When one note is playing, that’s what you’re conscious about. Then the next note starts playing, and that’s what you’re conscious about. These things come on and off constantly, and there’s this appearance of unity to it all, but in fact it’s each of these separate circuit systems being enabled and being expressed in a particular moment in time. Consciousness is not a thing in the brain that information gets poured into and you’re aware of it. It’s the constant struggle of all these circuits to come up to the top and hold the stage for that second.

Zimmer: And yet, as central as consciousness is to our sense of being human, we mostly experience it in the context of our other quintessential trait, sociability. We speak to each other with language and then start to have a sense of what other people are thinking. Rebecca, you’re involved in this fast-moving area of research. How are we beginning to explore the social brain?
Rebecca Saxe: Through most of the short history of neuroscience, what we’ve been able to study are the kinds of things that brains in general do—the things that brains of all kinds of animals can do. Studying these functions in nonhuman animals has given us the most detail about how neurons get put together to do complex functions because we can really look, neuron by neuron, at how vision gets put together, how motor control gets put together.

This has led to a focus on those functions that our brains share with other animals. But for any parent watching a child grow up, these are not the most striking functions. Although it’s fabulous when kids start to walk, what’s amazing is to watch a kid start to interact socially.

For example, one of the key things 11-month-olds will do is point. In experiments where the researcher doesn’t respond, these children wait for the person to follow and look. They’re not happy when you just look. They want you to look back at them and confirm that not only did you look, but you looked because they told you to.

People have been looking at our closest evolutionary neighbors, apes, to see if this is a common thing across all animals or if it’s something that humans do specially. What we’re finding is that deliberately trying to get somebody else’s attention seems to be something human beings do that none of our ape relatives do.

Because this function is unique to the human brain, you can study it only with tools that work in humans. Those technologies have really been available for only the past 10 or 15 years. What brain imaging has made possible is being able to take live human beings—we call them normal human adults; in my lab they’re MIT undergrads—put them in a scanner, and get them to do all kinds of things. We can have them talk or read or watch a video and we observe how their brains are processing information while they are doing it.

The general topic of social interaction is really important, but there’s a particular piece of it that links up to what Sam was saying earlier about how vision works. In vision we feel as if we’re getting a perfect view of everything the way it really is. We’re not missing anything. We’re not making anything up. That’s a useful and healthy illusion, but it covers up all the activity going on in constructing a visual image.

Social cognition is the same. We feel as if we can see what other people are thinking. We just know what motivates other people around us. In fact, there’s this very complicated and specific mechanism in the brain that is generating these inferences and these perceptions. My research is looking at where this kind of mechanism is. The next question is, how does that mechanism work? That’s a lifetime question.

Zimmer: There is a lot of work lately in understanding how perception translates into action, making sense of what goes on when we make a decision to do something.
Wang: Some neuroscientists who are studying these processes are interested in the idea that perhaps you could have a brain center that gathers evidence and reaches a threshold for making a commitment. There might be another brain center that expresses confidence in the decision or even the very awareness of the decision.

Here’s an example that many of you may have encountered from everyday life. You may be presented with a dilemma—say, whether to take a job in a new city. The pioneering psychologist Amos Tversky once did an informal survey over a period of years, asking people how confident they were that they were going to take such a job offer. There was a tendency for people to underestimate their own certainty in the decision. People would say things like “Well, I’m not sure. I’m inclined to probably take it, but I’m still thinking about it.” What Tversky found was that people almost always went and took the job.

So you can be pretty committed to a decision yet be unaware of it. In fact, if you are very close to someone—let’s say your spouse—he or she might be aware of your decisions before you yourself are. That’s an example in which your mental processes may not be available to you, but they are available to someone who knows you well. So something that we might imagine being integral to our consciousness is in fact composed of components that are not explicitly accessible to us.

Zimmer: Mike, you’ve been working with legal scholars to try to bring insights from neuroscience to the law. Are you making progress with that?
Gazzaniga: It’s a large project in which we’re trying to look at the impact of neuroscience on our sense of justice. A way to summarize the project is to say what one of the philosophers said in the study groups:? “We are the law.” It means that how we think about ourselves pretty much sets up the framework for how we deal with cheaters, people who are not doing their job, people who do harm, and all the rest of it.

When you have this basic insight, then you realize that new knowledge about who we are is going to change how we think about the law. How we think of ourselves, how we should think about punishment and retribution, and how we might want to change the way we deal with those things are the large questions that we’re considering.

The more immediate issue is that neuroscience is everywhere. So should it be in the courtroom? Is having a scan of somebody’s brain during a trial helpful? Lawyers like to put it in terms of “Is it prejudicial or is it probative?” Maybe just having a picture up of a brain prejudices the jury to think that we really understand something when actually all it is is a picture through a time point that may not in fact be telling you much at all. So one of the objectives of the legal project is to look at the issue of how much neuroscience should be in the courtroom and how much of it should not.

The field is vast, and we’re trying to narrow it down to a few questions. Then we’ll have a unique union of neuroscientists working with lawyers and jurists to sharpen a question by carrying out actual particular experiments.

Audience member?: Picking up on that theme of morality and responsibility, what goes on in the brain when someone can’t control their anger properly?

Saxe: One really interesting discovery about the brain is that one of the major ways it works is by generating all the possible responses to a situation and then inhibiting the ones that you don’t want.

When there’s a cup in front of me or a comb in front of me, most of the time I don’t drink from the cup, and most of the time I don’t pick up the comb and comb my hair. Especially I don’t comb my hair if it’s an inappropriate context, and I don’t drink from the cup if it’s somebody else’s cup.

You might think we generate the plan for how to reach for the cup and drink from it only if that is something we have decided to do. But it turns out, actually, that our brains are constructing representations for all the possible actions with all the possible objects in front of us and then tamping them down. You can see this in patients who have lost some inhibitory controls because they’ve had damage to their frontal lobes. You get what’s called utilization behaviors. You get people who, literally anytime you put a comb in front of them, will start combing their hair just because there’s a comb. They’ll use it. If you put a glass in front of them they’ll drink from it.

I think that’s probably also true of our emotional responses. There’s much more being generated and then tamped down. So one really important function our brain provides us is the ability to not act on all the possibilities that it’s generating.

Levitin: One of the most interesting and counterintuitive things I learned in my training is that what differentiates the human brain from those of other species is the huge, enormous size of our prefrontal cortex. You would think that what all this prefrontal cortex real estate would do for us is allow us to do all these wonderful things like paint and make music and speak and build churches and cities and schools and have systems of justice, but at an anatomical level one of its most distinguishing characteristics is that it’s full of inhibitory circuits.

Wang: The prefrontal cortex is often thought of as being responsible for carrying out executive functions: performing the considerations that come before action, planning for the future, acting on those plans, perhaps exerting will to make a good impression on someone in a job interview or in some other kind of controlled situation.

I feel tempted after this very cerebral discussion to give you a piece of practical advice. These acts of willpower and control in the prefrontal cortex are things that you can exercise like a muscle. There are mental resources. The brain changes in response to the environment, and you can in fact increase the amount of willpower you have by practicing something. As an example, if I give you a bunch of cookies to eat and then I give you an impossible puzzle to solve, you’ll persist in that puzzle for some time.

Now, if instead of giving you cookies I give you a bowl of radishes to eat—most people don’t like raw radishes—and then give you the impossible puzzle, you’ll persist on the puzzle for about eight minutes less. There appears to be some finite mental resource of willpower. You willed yourself to eat the radishes and you depleted that resource. Psychologists refer to this phenomenon as ego depletion. You have less willpower for the next thing.

But it turns out you can actually build up willpower like a muscle if you can do something that requires effort of will—something as silly as brushing your teeth with your nondominant hand. If you brush your teeth with your nondominant hand for several weeks, you increase this reserve pool of mental something. I’m not going to say what that something is because it’s not known, but that mental something is available for other tasks. You can actually build up whatever it is that is responsible for willpower.

So this business of planning for action and all the things that come before action turn out, like many mental capacities, to be a thing that you can practice at and improve.