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.

 

Four ways breast milk is really interesting

You might have heard a lot that breastfeeding may reduce the risk of infections, allergies and gut problems. But it’s perhaps even more fascinating than you realise.

1. Mums may produce different breast milk for sons and daughters

Dr Katie Hinde from Harvard University studies lactation in monkeys to understand how breast milk provides not only nutrition, but shapes immunity, nervous systems and behaviours in their offspring.

Her team has found that even a monkey mother’s own breast milk can vary in the composition of fat, hormones, protein and minerals. It can depend on her age, how many children she’s had and what she’s been eating now and in the past. But, as this Naked Scientists interview explains, it even matters whether she’s had a son or a daughter.

Rhesus macaque monkeys produce more, lower energy milk for daughters, but less, higher energy milk for sons, in such a way that the overall energy supplied balances out. Why this is is unclear and Dr Hinde’s team is working to unpick these tricky questions. The monkey mothers also produce more calcium for daughters, which Dr Hinde speculates is linked to a quicker development of daughters’ skeletons.

As the interviewer, Kate Lamble asks, how do the monkey mums know whether it’s a son or daughter? Dr Hinde thinks it’s probably down to more hormones produced during female foetal development affecting mammary glands. It could also be behavioural interactions between mother and offspring after birth.

The big question is, does this hold true for humans? Is this something that mattered more in our evolutionary past, but is less relevant in our cosier modern world?

2. Time of day matters

Many animals exhibit day-night rhythms that can affect everything from sleep-wake cycles, metabolism, immune responses and heart rate. And it seems breast milk production is no different.

Milk produced during the night contains higher levels of a hormone, melatonin, which is known to regulate day-night (“circadian”) cycles. Researchers have suggested this can help reduce irritability and prolong night-time sleep, but more work is needed to show this for sure. Adults can manufacture melatonin from essential molecules taken in through the diet, but babies can’t.

Other studies have focused on tryptophan – an important building block in the body’s biochemical manufacturing of melatonin. One study linked higher levels of tryptophan in breast milk at night with a rise in melatonin in the breast-fed babies, which was also associated with more sleep.

To try to establish whether elevated tryptophan caused improved sleep (rather than because of some other differences between breast- and formula-fed babies), another study compared babies who were fed formula milk with added tryptophan at night, added tryptophan in the day and with no added tryptophan at all. Only babies fed added tryptophan at night had better sleep and metabolites in the urine suggested this was down to the production of more melatonin.

Whilst the overall effect on babies’ sleep and whether fluctuations in the makeup of breast milk can really cause changes is still to be fully teased out, these findings suggest that mothers who express milk for their babies for a later time may want to pay attention to what time of the day they did it.

3. Hormones in breast milk can affect behaviour too

Hormone levels, such as cortisol, can naturally fluctuate throughout the day. Cortisol, in particular, is not only important in the stress response but is needed in the mammary glands to stimulate new milk production and protect the survival of mammary cells.

Researchers comparing breast- and formula-fed babies have suggested that higher cortisol levels in milk are associated with more fearful babies. Others studying monkeys and humans have reported levels of maternal cortisol affecting temperament in three-month olds, and this may differ for sons and daughters. For some animals, like red squirrels, it may give them a competitive advantage – cortisol-like hormone levels rise as a forest gets more crowded, which accelerates the growth of their offspring.

Back to Katie Hinde’s research. Again, studying rhesus macaques, her team wanted to know whether these effects were genuinely down to cortisol or because of variations in the amount of nutrients passed on (which are in turn affected by hormone levels). The researchers measured milk one month after birth, and again three to four months after birth. Generally, higher levels of cortisol in milk were associated with babies who scored higher for nervousness and lower for confidence.

But why? They point to evidence that elevated cortisol in humans may lead to reduced growth, and speculate that there may be a trade-off between infant temperament and growth – if more nervous, less confident behaviours reduce activity, then the available energy from milk can be put towards growth, particularly for sons. This may be particularly crucial in times when resources are scarce or competition is high.

At least in rodents, the receptors for these hormones are most abundant in the gut in infancy, before declining into adulthood. This suggests that babies of at least some animals may be taking an active role in sensing the environment through their mother’s milk.

 

4. Breast milk may shape the friendly gut bacteria

Californian researchers compared the bacteria in the intestines of breast- and bottle-fed baby macaque monkeys between five and 12 months old. They also took blood samples to analyse the immune cells in the growing babies.

The bacteria profiles in each group showed stark differences. The breast-fed babies contained higher levels of Prevotella, Ruminococcus and Lactobacillus, whilst the bottle-fed babies had higher levels of Clostridium. The immune systems of the two groups also differed. Breast-fed babies had more immune ‘memory cells’ and ‘helper cells’ (which help fight off foreign invaders) and produced a sturdier immune response when isolated blood cells were challenged. The researchers noticed differences in chemical signals in the blood known to influence how the immune system develops.

Another study, this time on mice, may give clues as to one way this can happen. By manipulating particular antibodies in maternal milk, these researchers showed that a lack of antibodies produced very different bacterial gut colonies and affected how well the mice could cope with an intestinal insult. Both studies showed that variations in bacterial profiles were still seen many months after the experimental diets ended, indicating that the effects on the immune system may be very long-lasting.

All this suggests that breast milk, possibly through the action of antibodies, causes certain helpful microbes to colonise the gut. These then produce a spectrum of chemicals that help shape the maturing immune system, making it better equipped to fend off infections and less likely to trigger allergic reactions.

The question is, for humans in today’s world, how much would these variations actually matter?

 

Dad With A Curious Mind

I’ve had a rebrand! The blog is now Dad With A Curious Mind. But my outlook hasn’t really changed.

I felt increasingly uncomfortable with The Skeptical Dad. I didn’t think it really represented me – I love what some skeptics do and share many values, but I don’t feel integrally part of a ‘skeptical community’ or ‘skeptical movement’. I dip in and out, with various blogs, events and podcasts, but I tend to leave it at that. A bit outside looking in.

So the new name seems to fit me better. I’m just curious about the world. Curious about learning new stuff and being amazed by the natural world. Curious as to how looking at evidence and taking scientific approaches can affect everything we do, including (and especially) parenting. And yes, some may say, just a little curious.

So please keep following, sharing and interacting. I hope there are other curious people out there too.

Welcome To Holland

I am currently working through a FutureLearn on ‘the genomics era’. The course introduced some of the genetic errors that can happen in certain diseases.

One of the errors occurs when cells divide to form reproductive cells (sperm or eggs) – a process called meiosis. Most cells in the body have 46 chromosomes, arranged in 23 pairs. Reproductive cells have half the number, so that when a sperm and egg fuse, the newly fertilised cell has the normal complement of 46.

Certain diseases, like Down syndrome, Edwards syndrome and Patau syndrome, are the result of an extra chromosome in the fertilised egg. So instead of 23 pairs, there are 22 pairs and one triplet (or ‘trisomy‘). This error occurs when the reproductive cells are made, if the chromosomes of the parent cell are unevenly split between two new daughter cells.

The course featured a moving video of two parents whose daughter was diagnosed with Down syndrome. The father explains a powerful analogy to capture the emotions and experience of being told of such a diagnosis. The essay, ‘Welcome to Holland’ written in 1987 by Emily Perl Kingsley about having a child with a disability, is narrated in the video below, and is incredibly touching.

Calling all science-y parents

It’s been a while since I posted on The Skeptical Dad. Since around the time our second one – a sceptical daughter – came along, in fact.

It turns out that having children vastly diminishes the time and energy for properly researched blogging. Or for anything, for that matter.

Who’d have thought?

I’ve got a stack of ideas jotted in random places and half-written posts waiting to be worked on. So I’ll get back to regular postings from now on.

Promise.

For now, here are a few things I’ve noticed in the last year or so, which might be interesting to science-y parents.

 

ExpeRimental

From The Royal Institution, the UK organisation dedicated to scientific education:

ExpeRimental is a series of short films that make it fun, easy and cheap to do science at home with children aged 4 to 10. Our films give you lots of ideas for kids’ activities that will help you explore the world around you, question and experiment together. We’ll show you how to do the activity and how to make sure adults and children get the most out of it. Tell us how you get on and share your photos and any funny things your kids say!

What I like especially about ExpeRimental is that it’s not just a series of fun activities (though it is) but it teaches a real scientific approach. By tweaking variables, predicting what will happen, then observing the effects, it takes these practicals from demonstrations to experiments.

Citizen science

The brainchild of Sophia Collins and funded by The Wellcome Trust, Nappy Science Gang is taking a citizen science approach to answer some key questions.

…it will be the first citizen science project where the users set the research priorities, design their own protocols (with advice from scientists) and then run their own experiments. We’ll find out some useful science for cloth nappy users (a growing group as the environmental imperatives become clearer), and we’ll tackle a lot of persistent urban myths, with scientific thinking and evidence.

Find out more and get involved at the Nappy Science blog and Facebook page.

Introducing kids to evolution

Here’s a great resource for books on evolution and Charles Darwin aimed at kids, courtesy of Evolution for Kids!

 

Happy science-ing!

Does breastfeeding ‘cut leukaemia risk’? No good evidence

Occasionally my work and home life collide – I read some stories in the press about research claiming breastfeeding for six months or more could cut the risk of childhood acute leukaemia. The research was shaky, so I wrote this for the Leukaemia & Lymphoma Research blog (where I work).


 

Reports coming out in the media (such as Express, Mail, Mirror) are suggesting that breastfeeding for six months or more can lower the child’s risk of developing leukaemia. But where did these findings come from and how reliable are they?

In this post, we take a look at the research that led to these reports, and suggest that the results are not very robust, the conclusions are overstated and the claims likely to cause unnecessary alarm.

Greater than the sum of its parts?

The new research, published in the peer-reviewed journal JAMA Pediatrics, combines many previous studies that looked at whether children who had been breastfed (and for how long) went on to develop childhood leukaemia. The studies in the new analysis were a mixture of size and quality, so on their own couldn’t lead to any definitive conclusions. But when put together and re-analysed – known as a meta-analysis – it is intended to boost the power of the findings.

The new study includes 18 studies that met a certain quality threshold. The researchers, based at University of Haifa in Israel, report that children who had been breastfed for six months or more had up to a 19% lower risk of developing leukaemia than children who had never been breastfed or had been breastfed for under six months.

From this, they conclude this is sufficient evidence of a protective effect to further promote the health benefits of breastfeeding and encourage greater uptake amongst new mothers.

But we are not persuaded these claims truly stack up.

Correlation is not causation

The strength of a meta-analysis is that it tries to make sense of all the best research on the subject. But all of the studies within the new analysis looked at the association between breastfeeding and leukaemia, and therefore cannot tell you about true causes. Other background factors that affect both the likelihood of breastfeeding and leukaemia risk could have been missed or overlooked.

For example, parental affluence may affect the decision to breastfeed. But affluence will also affect a host of behaviours, like attendance at nursery, exposure to infections, decision to vaccinate, time of weaning, and many, many more. We don’t know for sure what factors do influence leukaemia risk – and parental affluence is just given as an example here merely to illustrate the complexity of background factors – but simply linking breastfeeding and leukaemia risk without consideration of other potential influencing factors is far too premature.

Experts who conduct these types of studies are well aware of these issues and always attempt to account for background factors, like socio-economics, lifestyle, gender, ethnicity, and so on, but it’s always hard to eliminate them altogether. Nevertheless, we were alarmed when we spoke to our statistical experts who noticed that the meta-analysis unusually relies on crude data that did not appropriately account for background factors.

They suggested that the authors’ relative inexperience with this type of analysis has led to a number of flaws.

Hidden biases

The experts we spoke to pointed out a gross error in the data – one dataset, that had been used in two different publications, is included twice. This could distort the statistical robustness or the size of any effect, and could be serious enough to consider a correction or withdrawal of the paper.

There are also a few ways these data could have been skewed to give wrong or exaggerated results. One is a bias in those participating in these studies. Many were based on phoning mothers at home or by a self-administered questionnaire. This introduces a potential participation bias, where the people surveyed and who agreed to take part were not representative of the population as a whole. This may mean certain groups, such as more educated or time-rich parents, were overrepresented in the comparison group (children who didn’t get leukaemia), suggesting a larger proportion of children who did not get leukaemia were also breastfed.

Almost all of the studies asked mothers or parents to remember the duration of breastfeeding, sometimes many years later. This introduces a possible recall bias, where parents may not have accurately remembered what they did or their responses were affected by knowing that their child had had leukaemia. And because childhood acute leukaemia is thankfully relatively rare – only three to four children in every 100,000 are affected each year in the UK – the small numbers could have inflated these biases.

It would be far better to recruit a large random sample of people, collect data in real-time, and then look at whether children went on to develop leukaemia. This is more costly and time-consuming, but it would help diminish some of these potential biases because the particpants and research questions would be defined up-front. 

The authors acknowledge these limitations in their discussion section of their paper, which is why we were surprised by the strength and certainty of their claims in the conclusions section.

What would this mean in the real world anyway?

There is some evidence that links proper immune system development to a reduced likelihood of developing leukaemia as a child and certain genetic faults present at birth can raise the risk substantially, but we are still far from truly understanding all the many different factors at play. It is an important area to be able to understand who is most at risk and what factors can alter their likelihood of developing this disease if we are to prevent some of these cases, but we are not convinced that this new analysis provides strong evidence for a significant role of breastfeeding.

We should also stress that because of the relative rarity of childhood leukaemia, even if the authors’ claims were true, it would still affect only a tiny number of children. And it would still only affect children who are already at risk because of key genetic faults that occur in the womb.

There is a lot of pressure on new mothers, some mothers cannot breastfeed and many factors can affect how long new mothers can breastfeed for. Parents of children who develop leukaemia can also feel a lot of guilt, even though we know some children will unfortunately get the disease whether they’ve been breastfed or not.

Stories based on problematic research do not help anyone.

  • For some expert opinion, including our Research Director and Prof Eve Roman (an epidemiologist whose work we support), see the Science Media Centre
  • Reference: Amitay & Keinan-Boker (2015). Breastfeeding and Childhood Leukemia Incidence A Meta-analysis and Systematic Review. JAMA Pediatr. 2015;169(6):e151025. doi:10.1001/jamapediatrics.2015.1025

What can Mickey Mouse tell us about a growing child?

At a party some time ago, I got talking to a biology graduate friend about comparative psychology, as a geek tends to do at social occasions.

Comparative psychology is the study of animal behaviour and mental processing across different species. By doing this, it gives us clues to the function, benefit and development of a particular behaviour. Understanding the similarities and differences amongst different animals in this way can shed light on evolutionary relationships.

The topic came up because our friends were revelling in how cute baby animals are. If you don’t believe me, just look at these cherry-picked examples:

Author: George Estreich

Baby monkey

Author: Ville Miettinen

Baby fur seal

Author: Matt Stanford

Baby elephant

Author: uaeveggies

Baby duck

What’s striking is how wildly different baby animals can provoke the same “aaah” reflex. Baby primates and baby birds, separated from each other and from us by millions of years of evolution, can elicit the same cooing reaction. And size doesn’t seem to matter − a 100kg baby elephant can bring as much infatuation as a 5kg baby seal.

In other words, there’s something about being a baby, and not just a miniature version of an adult.

This immediately reminded me of an image drawn by Nobel prize-winning animal behaviourist, Konrad Lorenz. It shows how juvenile proportions are conserved across different animal groups, and goes someway to explain why we react to many baby animals as we do.

From Studies in Animal and Human Behavior, vol. II, by Konrad Lorenz, 1971. Methuen & Co. Ltd.

From Studies in Animal and Human Behavior, vol. II, by Konrad Lorenz, 1971. Methuen & Co. Ltd.

I think I first saw this image in a book by renowned evolutionary biology, Steven Jay Gould*. He also included it in a wonderful essay called Homage to Mickey Mouse. In this article, Gould explains that over time, to chime with his softening of character, Mickey’s appearance became increasingly juvenile.

via Zoonomian

A large head relative to body, short legs and feet, bulbous cranium and big eyes, as seen in a latter-day Mickey, look like the hallmarks of a juvenile. And Mickey travelled this path to juvenility in reverse − a phenomenon known as ‘neoteny‘.

An illustration’s fine, but to truly demonstrate this scientifically, Gould actually measured the relative changes in Mickey’s physical attributes and plotted the results on a graph. The result, as was Gould’s wont, is an engaging fusion of science and creative writing − do read it. (On reading, I did wonder whether Mickey’s appearance was altered to match a desired change in character, or the other way round.)

The key to all this is that the proportions of a baby’s face, as compared to an adult, are similar across many different animals. This set of features triggers what Lorenz described as an ‘innate releasing mechanism’ − an automatic and consistent reaction to an important behavioural cue. It makes sense that a hard-wired mechanism has evolved to trigger an immediate sense of attachment when confronted with a baby’s face − it will promote parental care, which has clear evolutionary advantages.

But that same hard-wired mechanism also appears to fire when we see similar baby-ish proportions in other animals. It’s an inappropriate response in an evolutionary sense, but it’s better to be harmlessly fooled by a baby bird than to not feel instinctively drawn to our own baby.

What’s fascinating is that, in some cases at least, these ‘releasers’ are reduced to very specific features. A classic example was demonstrated by Lorenz’s Nobel prize-winning collaborator, Niko Tinbergen, using three-spined sticklebacks. A male stickleback will attack another male, as identified by a red belly, but will also attack any object with a red spot − fish-shaped or otherwise. A stickleback-shaped object without a red belly is suitably ignored. Like a red rag to a stickleback, it’s better to be safe than sorry.

Babies do something similar in reaction to stylised smiley faces − a circle for a head, two dots for eyes, and a curved line for a mouth is enough to grab a baby’s attention. This stays with us into adulthood and is, for better or worse, the reason why emoticons are so enduring. So, similar to a stickleback reacting solely to a red spot, it seems it’s not a whole baby’s face we respond to, just a certain set of features.

Yes, your baby’s cute because of this graph:

“At an early stage in his evolution, Mickey had a smaller head, cranial vault, and eyes. He evolved toward the characteristics of his young nephew Morty (connected to Mickey by a dotted line).” By Steven Jay Gould

* I should dedicate this post to the late, great Derek Yalden, who taught me zoology at The University of Manchester and told me to read The Panda’s Thumb.

(As an addendum: none of this makes animals we find cute any more ‘worthwhile’ than “ugly” animals. Check out the recent campaign by the “Ugly Animal Preservation Society“.)