Jonah Lehrer explores why we are more likely to trust people when we're holding a warm cup, and why cigarette addicts should blame the insula portion of their brains:

[The insula] detects the bodily changes associated with smoking – the escalated pulse, the slow inhalation, the slight nicotine rush – and combines those physical sensations with the idea of a cigarette. Over time, these bodily cues lead to the development of an addiction: When we crave a cigarette what we are actually craving is this sequence of fleshy feelings.

On a related note, Jon Hamilton spoke with Yale University brain scientist Ralph DiLeone on the connection between eating and addiction. DiLeone explains why the toughest habits to break can be those developed in childhood:

The motivation to take cocaine in the case of a drug addict is probably engaging similar circuits that the motivation to eat is in a hungry person. ...That doesn't necessarily mean food is addictive the way cocaine is, DiLeone says, but he says there is growing evidence that eating a lot of certain foods early in life can alter your brain the way drugs do.