Tag Archives: neuroscience

Does a rub or a cuddle relieve pain?

I suspect most parents will have been there with a little one – a fall, a knock, a misfired football, and then the tears. In a bid to relieve the hurt, you give the sore a good rub, a strong cuddle or maybe a peck to ‘kiss it better’.

But why? Does a rub genuinely relieve pain, or is it just the only thing we can think of to show we care?

What is pain?

First, we need to understand what pain is.

Our skin and tissues underneath have different types of nerve cells coarsing through them. These help the brain sense the environment by signalling touch, temperature, pain, depending on what the fine nerve endings are set up to detect. Some nerve cells, for example, are studded with molecular receivers that grab chemicals wafting over them or change shape with varying temperature, while others fire when bent, stretched or vibrated.

When stimulated, the nerve cell pings an electrical signal down to our central nervous system, which then uses all the messages to interpret what’s going on in the environment and elicit the most appropriate action.

A gentle touch or a warm fire, will trigger our mechanoreceptors (touch) or thermoreceptors (temperature) and we may experience a nice fuzzy feeling. Pain receptors, technically known as nocireceptors, have a high threshold for stimulation. So we feel pain when certain stimuli – temperature, pressure, chemical – are intense enough to trigger the high threshold nocireceptors, which fire off signals that our brain processes as “too hot”, “too hard” or “too irritating”. This helps us take immediate action (‘move away!’) and means we generally learn what’s safe and what’s not. And while it might seem attractive to not feel pain, it causes serious problems if it isn’t there – individuals without this sense are prone to chewing chunks of their tongues off or to frequent bone breaks.

What shapes the feeling of pain?

One idea of pain relief says that stimulating the mechanoreceptors with a rub ramps up the ‘touch’ signals being sent to the central nervous system, which at least partly overrides the input from the nocireceptors. Known as the ‘Gate Control Theory‘, this shifts the balance of sensation from ‘pain’ to ‘touch’ – in a way, distracting our central nervous system with another stimulus.

There is also a special class of slow-acting touch nerve cells, triggered by gentle stroking, which seem to signal pleasurable sensations. Some studies suggest that these interact with the pain pathway to dampen painful sensations.

As well as the signals from the body, the brain coordinates input from other processing centres, which allows us to take into account past experience, from where on the body messages are being received and the context in which the stimulation is happening. Maybe that’s why a hug from a loved one can feel extra comforting.

And chemical signals in our brain shape our feelings of pain. Endorphins are chemical signals that are natural opiates so, like morphine and other opiates, can block painful sensations. They are also released in response to stress and fear, and bring the energising and euphoric feelings after exercise. Sometimes their effects are powerful enough to completely override the pain, which can be why people who have been shot sometimes only feel pain after the fearful situation has ended.

The relief of a rub

So what we actually feel is a physical and emotional experience after the brain processes the various sensory signals from the body, and takes into account past experience, environment and mood.

These may be some of the reasons why a good hug or rubbing a painful area can bring some genuine relief from hurt.

 

Does the sun make you sneeze?

This is a video I took of our little one, sitting in a chair watching telly. As I walk over to him the sunlight streaming in through window catches him full in the face, and a couple of seconds later he sneezes.

This happens to him fairly often, usually as we leave the house into the bright sunlight. I noticed this behaviour straightaway, as the exact same thing happens to me when I move from dark to bright light.

It turns out that this doesn’t happen to everyone, as I found out when I said casually to friends, “you know how the sun makes you sneeze, well…”, and was met with stony silence.

Then I found out I had a proper disorder. Gosh!

It’s called a photic sneeze reflex, or as some witty scientists labelled itAutosomal dominant Compelling Helio-Ophthalmic Outburst – ACHOO syndrome for short. It is estimated that 17-35% of the population have it, and it’s far more common in white people than in other ethnicities.

But no one knows why it happens. Despite it apparently being noticed by Aristotle and investigated by philosopher Francis Bacon, little research has been carried out. My search in the biomedical database PubMed turned up only 16 research papers since 1984.

The best guess at the moment is that it’s because the nerve cells that carry information from the eye and those that carry information from the nose run so close together. As the nerves from the eye are stimulated by bright light, usually to constrict the pupil, electrical signals ‘spillover’ and activate the nerves coming from the nose. This causes the brain to confuse a bright light with a nose irritation, and… ACHOO! In fact, the area of the brain responsible for processing visual information is overstimulated in photic sneezers compared with non-sneezers, which may underlie the spillover effect.

We do know that it appears to run in families – as it has seemingly done in our case – but the genes at the root of it are not known. Initial studies claimed that a child has a 50% chance of inheriting the ‘disorder’ from a photic sneezing parent, but there may be more than one ACHOO gene.

It’s a fairly harmless reaction, though the US air force were sufficiently concerned to fund research into whether this reflex could endanger jet pilots. It could, but was easily overcome with sunglasses.

You may be tempted to speculate as to whether it evolved for a purpose. In all likelihood it didn’t, it is a quirk thrown up by evolution but one that’s not disadvantageous enough to be selected against.

It is irritating, but at least it doesn’t happen during sex.