PASCAL GOETGHELUCK / SCIENCE PHOTO LIBRARY PASCAL GOETGHELUCK / SCIENCE PHOTO LIBRARY
Smoking brain effects. Coloured positron emission tomography (PET) scans of the brains of a smoker (bottom) and a non-smoker (top) showing the levels of monoamine oxidase B (MAO B). This is an enzyme which breaks down dopamine, a neurotransmitter chemical involved in motivation and behaviour. MAO B levels are colour-coded: red (highest) through yellow and green to blue (lowest). The smoker's brain is seen to have much lower levels of MAO B, which leads to higher levels of dopamine being present. As dopamine is involved in reinforcing behaviour, this may partly explain the addictive nature of tobacco smoking.
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