We Seem To Treat Physical Warmth As A Sign Of Safety

When we learn that something in our environment signals Threat!, we start to react to every encounter with the "fight or flight", or "fear", response.

Recent work has shown, though, that the presence of someone we're close to — a friend or partner, say, — can reduce or even eliminate this response. Our brains seem to treat such people as a powerful "safety" signal.

This was thought to be a unique effect. But now a team led by Erica Hornstein at UCLA has shown that physical warmth does the same thing. The work, published in Emotion, was prompted by research finding that we implicitly associate physical warmth with social support. It has potential implications for treating anxiety disorders, especially for people who live alone — or who find it hard to unlearn links between certain stimuli and threat, as can happen with post-traumatic stress disorder (PTSD).

In the first of two studies, every time 31 participants were given a rubber ball, a soft fuzzy ball or a heated pack to hold, they were then given an electric shock. The shock was at a level that the researchers had previously established would be extremely uncomfortable, but not painful. One stimulus — a wooden block — was never paired with a shock.

The participants' skin conductance (sweatiness) was monitored. This data showed that they quickly developed a fear response to the rubber ball and the fuzzy ball, but not the wooden block — or the warm pack. The warmth seemed to stop them from learning to associate the pack with a threat. When the team then gave the participants all the objects in turn, but without any shocks, the rubber ball and fuzzy ball still triggered a fear response (while the warm pack still did not).

A second study on 30 people supported and extended this finding. This time, the team paired pictures with electric shocks, so that participants developed a fear response to these pictures. They then showed participants the pictures again, while they held either a warm pack or a rubber ball. The warm pack, but not the ball, completely inhibited the fear response.

The team would love to see work exploring how, exactly, both supportive others and physical warmth interfere with the fear response. One possibility is that it's to do with endogenous opioids — which have been found to be released both when we're with a close other and by warmth, and which are known to affect fear learning.

It's not yet known whether the warmth effect is innate, or reflects the learning in early life of an association between warmth and the presence and protection of a caregiver, which leads us to perceive warmth as a signal of safety. But however this effect works or emerges, the fact that it happens automatically is important.

Earlier work has certainly found that we can learn that certain stimuli signal "safety". But, because this learning happens through classical conditioning, these "learned safety signals" really only work for the specific unpleasant event used in the training, the researchers point out.

There's also some evidence that they can even hinder fear reduction in the long term. But supportive others and physical warmth seem to have a more fundamental, blanket, ongoing effect.

For this reason, the researchers see potentially important implications for treating all kinds of anxiety disorders. Perhaps treatments that involve supportive others or — especially for people lacking in strong social bonds — physical warmth could be more effective than current methods for helping people with phobias or PTSD, for example.

Clearly, there's important work to be done. But I, for one, can't wait to hear what comes out of it.

Further reading

– Warm hands, warm hearts: An investigation of physical warmth as a prepared safety stimulus.