Why do some people love speed when some others don't? To find out Jeremy Clarkson takes his mother on a rollercoaster, rides with the British Army bobsleigh team and visits California to investigate dragboat racing. Formula One World Champion Damon Hill explains how he thrives on thrill-seeking, artificially creating pressure in situations. Clarkson learns that enjoying thrill-seeking is a result of dopamine, a hormone released by the brain to provide enjoyment and serotonin a chemical that causes a person to feel frightened. The amount of these chemicals released during an activity vary from person to person.

• Jeremy Clarkson