Michael Mosley concludes his series on the history of experimental psychology by looking at how experiments on abnormal brains have revealed the workings of the normal brain. He meets remarkable individuals who suffer from rare conditions and unique circumstances including the case of an amnesiac known for years only by his initials, HM, who became the most studied individual in the history of psychology and whose extraordinary case opened a window on how the memory works.
Humans are very sensitive to touch and different parts of our body have different sensitivities. In fact, when it comes to our sense of touch, humans are similar to elephants. The different density of touch sensors in the skin, in different parts of the body, explains why some parts of the body seem to have a much lower pain threshold. A microscopic splinter in a finger can be extremely painful, while a cut on your leg may not hurt as much! Ultimately, pain involves much more than what's happening with the touch sensors in the skin. It has a lot to do with what's going on in the brain.
We set out to discover the biological reasons why humans eat such a range of diverse tasting dishes, and watch while contestants at a chilli eating contest push their taste buds to the limit. Compared to many animals, humans have a try anything once attitude to food and this has allowed us to populate every corner of the planet, while many other animals depend totally on one food source for their energy, which limits where they can survive.
A baby's brain is a mystery whose secrets scientists are just beginning to unravel. The mystery begins in the womb - only four weeks into gestation the first brain cells, the neurons, are already forming at an astonishing rate: 250,000 every minute. Billions of neurons will forge links with billions of other neurons and eventually there will be trillions and trillions of connections between cells. Every cell is precisely in its place, every link between neurons carefully organised. Nothing is random, nothing arbitrary.
A child's brain is a magnificent engine for learning. A child learns to crawl, then walk, run and explore. A child learns to reason, to pay attention, to remember, but nowhere is learning more dramatic than in the way a child learns language. As children, we acquire language - the hallmark of being human.