The Hello, welcome to the naked scientist with me Chris Smith and also with Cat Arnie.

Later in the show we'll be finding out how to save a life from doctors and paramedics performing open chest surgery in the street to helping people recover from severe and life altering brain injuries.

Plus in the news this week, a real invisibility cloak,

how caffeine gives us a boost,

and why scientists need you to quiz your dog.

The Naked Scientists Podcast is powered by UKfast.co.uk.

I don't know about you but I certainly can't start my mornings without several mugs of strong coffee and now

researchers have discovered just how much of a boost caffeine gives us.

Surprisingly drinking it at night may affect you more than you might think.

Grey Jackson went for a cup of with study author John O'Neill.

Sleep is regulated by two processes. One of them is a homeyostatic trive. The longer you've been without sleep,

the more you need to sleep. But the other part of when we sleep is the circadian rhythm, and the

circadian rhythm controls when we're most likely to go to sleep.

And so the first aspects of how caffeine works has been studied quite intensively

over the last few decades, but no one had really addressed the extent to which the body clock is affected by caffeine.

And so that's what we looked at.

And how did you go about looking at that?

Over in the states at the University of Colorado in Boulder my colleague Ken Rice took

several individuals and placed them in constant conditions for 49 days and

what he did was give them either a placebo pill or caffeine and then

look at how the melatonin was affected by caffeine. Now just to tell you

about melatonin it's the main hormone of

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