One of the biggest complaints that doctors hear is that their patients feel tired all the time. So common that it even has its own doctor's acronym: TATT. So two pairs of twins are going to find out if there is a way to combat exhaustion with two popular sleep regimes.

First, Hugo and Tina are testing the traditional technique - getting an early night. Sleep scientists call it sleep banking and the idea is that when you are tired, you are running a 'sleep debt'. To overcome tiredness you need to pay back that debt back by getting more sleep than you usually do. But it goes further than this - if you know that in the future you will feel tired, sleep banking can let you store up excess sleep for use later on. It is a controversial theory that our twins are going to test out in one of the most extreme experiments of the series - that is going to require them to stay awake for close to 36 hours.

Meanwhile their identical twin siblings will also experience the same 36-hour challenge but will be testing a technique popular with pilots, truckers and doctors - power-napping. The theory is that a 20-minute micro-sleep can give the brain sufficient rest that the onset of tiredness can be kept at bay. But will it work?

Once the challenge is over, the tests can begin. A lack of sleep affects risk taking, communication, memory, coordination and reaction time, so Chris and Xand have found the ultimate way to test everything - in a 747 simulator. All our sleep-deprived twins must attempt to land a 747 while being talked in by air-traffic control. As their tiredness levels get dangerously high, will either regime be able to combat exhaustion or will all our twins crash and burn?

Next is a story about the future of learning where Chris and Xand put their own identical twin bodies on the line to learn a new skill pitting real-world learning against the virtual world. Astronauts, engineers and even sports-stars are now training using virtual reality and it is touted as being the next big thing. But can learning in the virtual world really beat the real deal? To find out, Chris and Xand are going to try their hand at baseball - something they have never tried before. Chris plunges headlong into his virtual reality set up assisted by neuroscientist Dr Jack Lewis. Immediately, he is surprised to find out that there is some real science behind this latest trend. In fact, the software is so good that even though he is not hitting a real ball nor holding a real bat, his brain is learning how to plot in space where he needs to swing for a home-run.

Xand on the other hand learning to play baseball courtesy of man versus machine. He is facing down an automated firing machine which repeatedly pelts balls at him. Clearly, this is a technique that we know can work but it does have disadvantages - it is tiring, it is not as easy as doing VR in your living room and it is even giving him blisters. But after two weeks of training, it is time for the virtual versus reality finale. Chris and Xand each face off against a pro-baseball pitcher. They each receive 30 fast-ball pitches and see who will knock this story out of the park? Will it a win for traditional or futuristic?

The third part of this episode involves the series' biggest twin experiment testing a new theory about smart phones. Over 37 million people in the UK have a smartphone but intriguing research suggests that even though your smart phone is touted as making you more efficient, it might actually be making you less intelligent - lowering your IQ simply by being close to you. We split our twins into two identical groups to take an identical IQ test in identical conditions (overseen by identical twin invigilators!). The only difference is that half our twins have had their phones taken away while the other have them on their desks.

The theory boils down to distraction. Most people check their phones over 80 times a day but because we all have a limited amount of attention the mental effort of trying to ignore our phones might cause us to run out of brain space. But will this theory really work out in practice? Show less