1. A mirror neuron is a neuron that fires both when one acts and when one sees an action performed by another. So, the neuron mirrors the behaviour of another, as though the observer was having the experience.

2. Our emotions spread via a wireless network of these mirror neurons, which allows us to empathise with others. If someone stubs their toe, the same areas in the brain light up as the person who stubbed their toe, and is why we flinch.

3. Research has found that 26 per cent of people show elevated levels of the stress hormone, cortisol, just by seeing someone who is stressed. Second-hand stress is much more contagious from a romantic partner (40 per cent) than a stranger but, when observers watched a stressful event on video with strangers, 24 per cent still showed a stress response.

4. So how do you change this response? A study has shown that if you create a positive mindset about stress, you experience a 23 per cent drop in the negative effects of stress. Instead of being frustrated at negative people around you, see it as a challenge to help someone be positive.

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