Howard Burton - Sleep Insights: A Conversation with Matthew Walker

Why do we sleep?

Its such a widespread, everyday phenomenon that its natural to take it for granted. But when you stop for a moment and think about it, puzzles abound.

Matt Walker, Founder and Director of UC Berkeleys Center for Human Sleep Science, puts it this way.

When you just back up and think about sleep generally, it seems like the very worst thing that could have ever been designed. Youre vulnerable to prey, youre not finding food, youre not socially interacting as a group, youre not finding a mate. It looks disastrous.

Theres a great quote from one of the founding fathers of sleep, Allan Rechtschaffen, who said, If sleep doesnt serve an absolutely vital function, its the biggest mistake evolution ever made.

So is it a mistake?

Not very likely.

For one thing, as Matt is quick to point out, sleep has been observed in every species that weve studied to date, which looks like overwhelming evidence of its universal significance: if sleep was not evolutionarily advantageous, surely other fitter, non-sleeping species would have emerged somewhere to conquer their sleeping counterparts, which presumably would have been pretty easy, given that their competitors regularly lie immobile for long stretches of time. But none have.

Which means, according to Matt, that far from being an evolutionary mistake, sleep is nothing less than a fundamental, core biological drive, together with eating, drinking and reproducing.

But still, what does it do, exactly?

Well, we dont have a complete picture, but recent strides in our understanding have been enormous.

I would say that twenty years ago the question was, What is the function of sleep? Nowadays, that question is essentially being turned on its head, Is there anything that sleep does not benefit? Is there anything that doesnt go awry when you dont get sleep? And is there anything that doesnt gain an advantage when you do?

Matts lab at Berkeley has been focused on the impact of sleep on brain function, but he is quick to point out that other core processes of the body also benefit from the restorative process of sleep.

As far as the brain goes, current research indicates that sleep is essential to two core functions: learning and memory, and regulating emotions.

When it comes to learning and memory, it seems that sleep acts like a sort of vital cleansing agent, allowing us to transfer recently acquired memories to long-term storage while refreshing our brains to enable new learning and memories during the upcoming day.

The metaphor Matt uses to describe this process is that of a USB stick transferring data to a hard drive. New memories and learned processes that are acquired throughout the day are lodged in the hippocampus region of our brain, which has a limited storage capacity and thus acts like this metaphorical USB stick. During sleep, this information is somehow transferred to the vastly larger storage space of the cerebral cortex, thereby simultaneously saving memories and thoughts for the longer term while also freeing up space in the hippocampus for the next days experiences.

But, even more intriguingly, thats not all.

What also seems to be happening during sleep is that youre testing out associations. Its a little bit like memory pinball. Youre taking what youve learned during the day and youre launching it up into this attic of everything youve learned in your past experiencethe cerebral cortexand you bounce it around these nodes up there.

It is this sort of activity, Matt speculates, that every so often allows us to come up with interesting insights while we are sleeping. After all, he pointed out playfully, When was the last time anyone ever told you that you should stay awake on a problem?

In summary, then, there seems little doubt that sleep has a profound effect on the brains capacity for both learning and memory. But what about this second aspect of emotional regulation? Whats that about?

The first thing to appreciate is that emotion, unlike learning and memory, involves a much greater amount of fine tuning. With learning and memory, presumably the more you have, the better. With emotion, on the other hand, both too much and too little are no good. And were starting to realize now that sleep will enable you to be in the optimal emotional state between too little and too much.

Extensive neuroimaging experiments with subjects entering the scanner with varying levels of sleep the previous night revealed that showing a series of unpleasant images to those who were sleep-deprived provoked a significantly stronger response in their amygdalathe brain region strongly associated with emotional reactionscompared to their well-rested colleagues.

The current thinking is that these amygdala responses are actively regulated by a very different area of the brain in the frontal lobes, with sleep somehow playing a vital role in the maintenance of the active connection between the two areas thereby ensuring that your knee-jerk emotional responses are put in proper perspective and dont disproportionately govern your state of mind.

But how does sleep actually do this?

The details are still fuzzy, but Matt believes that somehow sleep enables us to reprocess emotional experiences without the associated stress chemistry, thereby allowing the brain to rationally evaluate our daily emotional experiences and place them in their proper context.

If that sounds both vague and complicated, its probably because it is. Suffice it to say that weve got a long way to go before a complete understanding of the function and specific mechanics of sleep are fully understood. But one thing is clear as glass: however sleep works in detail, we simply couldnt function without it.

Sleep as an evolutionary mistake? Wake up and smell the coffee.