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Slate on the BrainDaniel Engber answers your questions.

Posted Friday, April 27, 2007, at 6:11 PM ET

Daniel Engber was online at Washingtonpost.com on Thursday, April 26, to discuss this week's special Slate issue, Brains!, about the human brain and recent research, including looks at brain scans, what religion does to your neurons, mental workouts, and more. An unedited transcript of the chat follows.

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Daniel Engber: The familiar saying that "we only use 10 percent of our brains" turns out to be entirely false. People got that idea because the brain is fairly resilient to injury. As Daniel Gilbert points out in one of our pieces, you can have a steel rod rip through a large portion of your frontal lobe and only suffer from mild personality defects. That doesn't mean that your frontal lobe is "untapped" -- it just means that many important functions are distributed throughout the brain, and that the brain has different ways of accomplishing the same goals.

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Burbank, Calif.: Mr. Engber, thanks for taking the time to answer some questions. My question is: Alzheimer's Disease runs in my family, so much so that my mother is now stricken with it and she's only 56. I know there might not be any fool-proof ways to prevent it, but I thought I would start by learning new skills (I'm 30 years old, by the way). I took a drumming class and I'm going to learn some Spanish. But I was also wondering if it might help to learn to write or perform other skills left-handed since I'm right-handed. Is there anything you can suggest?? (I also watch "Jeopardy!" and do crossword puzzles).

Daniel Engber: Thanks for the question. Right now I don't believe there's any solid evidence about whether doing crossword puzzles at 30 could stave off Alzheimer's down the road. As Meghan O'Rourke points out on Slate, we're still facing an evidence gap when it comes to "brain training." Drumming class and Spanish lessons do sound rewarding on their own terms, though...

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washingtonpost.com: Train Your Brain (Slate, April 26)

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New York: I find these sorts of studies fascinating but doubt that they will ever be conclusive. If evidence of brain activity means religious ecstasy is an illusion, then couldn't most any other human emotion be considered an illusion as well? For example, suppose I contemplate a beloved but absent person. This triggers emotions that are undoubtedly reflected in brain activity. If the activity is measurable, does that mean my emotions are not real? Or that the absent beloved is not real? What if that absent beloved is God? I don't mean to imply that brain activity can prove the existence of God or a relationship with God. Only that it can't disprove it either.

Daniel Engber: You're pointing out how tricky these concepts can be, and how easy it is to draw your own conclusions from brain-imaging data.

I would point out, though, that no studies at all have suggested that religious ecstasy is an illusion. If anything, they prove that a believer is telling the truth about being ... ecstatic. That ecstasy is as real as any other emotion.

But those same studies can't explain whether the ecstasy comes from God, or from another source.

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Chicago: Curious about your opinion. If one could take a person and make an exact copy of them, down to every last detail (cellular, physiological, etc), would that person be exactly the same as the original? Would the person have the same memories and skills?

Daniel Engber: My personal opinion? Yes. But the premise of the question is utterly impossible, so what does it matter?

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Greenwood Village, Colo.: If homosexual behavior is present in many different animal species and found in all human cultures today and throughout history, then I would assume that the trait would provide some evolutionary advantage. If it doesn't present an advantage, why hasn't the trait been selected against and lost from the genome of these different species?

Daniel Engber: Hmm, good question. I'd just be speculating -- I'm a journalist, after all, and not an evolutionary biologist. But off the top of my head I suppose it's possible that homosexual behavior comes along with a broader category of social or sexual behaviors that -- taken together -- provide some sort of evolutionary advantage.

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Geneva, Switzerland: I wonder why it is simpler to learn something if you form it like a game. I have for long now been active in various Web sites that allows you to create and play games around subjects you are interested in, typically learning where countries are, chemical abbreviations and other type of purpose games. So, in short, why is it simpler to learn something when you add some competition to it?

Daniel Engber: That's interesting -- I've noticed that, too. The obvious answer would be that the game gives you more motivation to do the learning. The more attentional resources you devote to a given task, the more effective you'll be at that task ... I know I pay a lot more attention to a game when I care about winning.