I woke up exhausted this morning. It’s not that I didn’t get a good sleep — I did. It was just an incredibly busy one, full of running, climbing and at one point flying across a room. As I opened my eyes to the new day, it took a few moments to realize that I had not, in fact, spent a night engaged in intense, impossible physical activity. “Our brains are not resting when we sleep,” explains Rahul Jandial, MD, PhD, whose latest book is “This Is Why You Dream: What Your Sleeping Brain Reveals About Your Waking Life.”

In it, Jandial, a Los Angeles neuroscientist and neurosurgeon, explores why the brain stays active even as the rest of the body is dormant, makes the case for nightmares, unlocks the health signals our sleeping minds may be trying to tell us and reveals the new science of how to potentially ourselves a more interesting, aware dream life. I talked to Jandial recently via Zoom about the mystical, sometimes “transcendent state” of dreaming, and why you can’t do math when you’re asleep.

This conversation has been edited and condensed for clarity.

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You open this book with the evolutionary case for our dreams. Why do we need to dream?

The answer is based on neurodevelopmental biology. The fundamental principle of neurons, neural tissue, is that either you use it or you lose it. When we look at brain activation, brain electricity and glucose utilization, our brains are not resting when we sleep. In fact, the electricity can be seen as equivalent. The question then is, what is going on with the brain activation? Imagination and emotion are being liberated, meaning those neurons are activated. They’re using up glucose, they're sparking electricity through neurotransmitters that typically aren't during waking life.

"My big theory is that it's high-intensity training for the mind."

My big theory is that it's high-intensity training for the mind so we're not constrained by just the limited parts of our brain we use during the day. It keeps our thinking creative, and it keeps us adaptive as a species. When you look at the waking brain and the dreaming brain, it's quite different areas, and they don't overlap much. My best guess, based on those principles, I think is a new and fresh look to dreaming, that it is not a restful state. It is vibrantly active.

Some of us always remember our dreams and seem to experience them very vividly, while other people say they never dream. They never think about their dreams; they never remember their dreams. Do you think our dreams then are having the same impact on us in relation to our waking selves?

The way to tackle that is to look at the dreaming pattern throughout life. We’ve all had a nightmare, we’ve almost all had an erotic dream at some point. We know what a dream is. They arrive as a universal experience. Clearly, we remember some dreams. Nightmares, in particular, by definition, wake you up and sear you with that memory. I feel like in adulthood we get this variety of dream recall.

"The dreaming brain turning into waking brain is not a crisp moment."

Those people who recall vivid dreams versus those who don't, they have the same brain electricity and the same brain glucose utilization between them. So I think the dreaming process is churning, no matter what the memory. The dream recall varies. And that residue you were talking about is very important. The dreaming brain turning into waking brain is not a crisp moment. There are a few seconds of lingering transitions, called sleep exit. That's an area where you can hold onto a dream memory. People can cultivate this a bit. You can recall your dreams more. Not always, not every time. But just to know that that capacity is there, albeit limited, is fascinating to me. It bookends the sleep entry period, going from waking brain to dreaming brain. There are a few minutes there were people like Salvador Dali said they extracted interesting ideas. So while the recall is variable, the dreaming process is happening robustly in all of us.

I would........

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