Your bones are savvy. They are light yet strong and they repair themselves when they break. What’s more – although you can’t tell – your bones continually renew themselves, replacing old bone for new.

This isn’t unique. Other tissues and cells (most noticeably skin) replace themselves. But bones do it with adaptation, adjusting to meet the body’s mechanical and physiological needs.

How does the skeleton achieve something so remarkable? New imaging technology is revealing a previously under-appreciated dimension of bones: the living cellular network built deep inside them. This living network is composed of the most abundant cell in bone: the amazing osteocyte.

Osteocytes (literally “bone cells”) are buried alive in bone tissue whenever bone is formed. They develop long branch-like dendritic fingers that infiltrate the tissue and reach out to interconnect with one another.

Living inside hard, rock-like bone, osteocytes have been difficult to study. They were considered inactive and uninteresting for a long time. They are now known to sense mechanical strains, orchestrate bone tissue renewal, and regulate calcium levels in the bloodstream.

Almost as complex as the brain

As more researchers investigate these cells and their network, the picture has become more elaborate. Osteocytes are clearly numerous and densely interconnected (see the image below), but putting an actual number on them had never been done. But it’s worth doing.

Numbers in biology help us discover new insights, so much so that researchers have set up a database and handbook of many “bionumbers” across many species, collected from the scientific literature.

For example, the number of synapses in the human neural cortex is estimated at 150 trillion. An MIT-led citizen science project involving 120,000 online gamers has already helped in understanding how the brain sees movement by mapping these connections through a project called EyeWire.

But why should anyone care about the number of osteocytes? Because, as well as controlling bone strength and the release of vital minerals such as calcium and phosphate into the bloodstream, there is now evidence that these cells might influence how your immune system works, how fat you are, how your kidney works, and even male fertility.

So, to get a sense of the size of the osteocyte network, we started to quantify it in the human skeleton. What we found exceeded even our expectations. It turns out that inside your skeleton lives a network that is almost as complex as the neural network of your brain.

How the numbers stack up

Taking recent imaging data (e.g. here and here), we calculated that the human skeleton contains about 42 billion osteocytes. That’s about six times the Earth’s population. In comparison, the human brain contains 86 billion neurons, packed in a volume (around 1.2 litres) comparable with that of the skeleton (which is about 1.75 litres). Although, of course, the skeleton is more spread out.

When we added together the length of these little cell fingers, imagining them being placed end to end, we found that this network is about 175,000 kilometres long. That’s more than four times the Earth’s circumference, and almost identical to the total length of axons in the brain: 180,000 km.

We based many estimates on simple algebraic manipulations of previously published data. But one essential piece of information could not be estimated easily: the number of connections osteocytes make with their neighbours. A brain without connections can do nothing, so estimating connections in the osteocyte network is important.

Unfortunately, connections between osteocytes are hard to see directly. What is seen instead are the little tunnels through the bone that osteocytes and their fingers live in.

So to measure this proxy tunnel network and the cell network within, we resorted to a mathematical model of dendritic finger branching. Feeding this model with data on the proxy network, we calculated that 23 trillion connections exist in the osteocyte network of the human body.

An evolved smart biomaterial

So, by these measures, your skeleton is a lot like your brain, with a similar number of cells interconnected in a similar sized space. But why do our skeletons need such a complex network? We don’t know exactly, but we do know that these cells exchange information, just like neurons do.

The tunnels that osteocytes occupy can still be seen in old bones, including dinosaur fossils. We can use this information to understand how bones have evolved to become the self-detecting and self-regulating biomaterial we own; that’s something that can’t be done with brain fossils.

Osteocytes communicate with each other about where the skeleton is weak and needs to be strengthened, or where there is damage that needs to be fixed. These messages are transmitted to cells on the bone surface that are able to remove damaged bone (osteoclasts) and form new bone (osteoblasts).

We know very little about how these cells communicate. But if we did, we could find better treatments for skeletal disorders like osteoporosis or osteogenesis imperfecta, and find ways to get football players back on the field more quickly (and more safely!) after a fracture.

In the meantime, the next time you stand up, walk around or do weights, think about how the network of osteocytes in your bones is responding to the stresses and strains you are putting it through. And thank your osteocytes for keeping your skeleton strong (and smart) enough to support you.

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It isn’t surprising that many Bostonians have vivid memories of the 2013 Marathon bombing, or that many New Yorkers have very clear memories about where they were and what they were doing on 9/11.

But many individuals who were not onsite for these attacks, or not even in Boston on April 15 2013 or in New York on September 11 2001 also have vivid memories of how they learned about these events. Why would people who were not immediately or directly affected have such a long-lasting sense of knowing exactly where they were and what they were doing when they heard the news?

These recollections are called flashbulb memories. In a flashbulb memory, we recall the experience of learning about an event, not the factual details of the event itself.

There might be an advantage to recalling the elements of important events that happen to us or to those close to us, but there appears to be little benefit to recalling our experience hearing this kind of news. So why does learning about a big event create such vivid memories? And just how accurate are flashbulb memories?

Strong emotions and personal connections

Not all historical events lead to flashbulb memories. An event must capture our individual attention and be identified as something significant before the memory is intensified. In order for us to exhibit this enhanced memory phenomenon, it seems critical that we feel a sense of personal or cultural connection to the event that results in a strong emotional reaction.

Hearing that a loved one has unexpectedly died would likely lead to a flashbulb-like memory, however, psychologists tend to study public events so they can examine a large number of memories referencing the same event. By doing so, investigators can examine the memories from a large group of individuals, often at varying intervals, to see how memories change over time.

Cross-cultural studies of flashbulb memories show that although the types of events and the memories that result are quite similar from person to person, the specific events that lead to these memories vary dramatically.

For instance, the 1977 study that coined the term “flashbulb memories” showed that although both black and white Americans almost universally recalled flashbulb memories of John F Kennedy’s assassination, black Americans were more than twice as likely to have flashbulb memories for the assassination of Martin Luther King, Jr than were white Americans.

Some theorists have argued that part of the reason that our flashbulb memories are so long-lasting is because having such a vivid memory is “proof” of our membership in a particular social group. It would be a poor patriot who could not remember what he or she was doing on September 11 2001.

Flashbulb memories have vivid details

The first description of flashbulb-type memories in the psychological literature (by F W Colgrove in 1899) is actually of Abraham Lincoln’s assassination and the sample report includes abundant, specific detail:

Everybody looked so sad, and there was such terrible excitement that my father stopped his horse, and leaning from the carriage called: ‘What is it my friends? What has happened?’ ‘Haven’t you heard?’ was their reply–’Lincoln has been assassinated.’ The lines fell from my father’s limp hands, and with tears streaming from his eyes he sat as one bereft of motion.

Although we can remember many events from our lives for decades or longer, it’s the particular ease with which these extremely vivid memories come to mind after lengthy, sometimes lifelong delays, that also makes them remarkable.

Compared to ordinary autobiographical memories, flashbulb memories include richer sensory detail. For example, you may readily be able to picture people and places clearly and to hear the sounds of voices and ambient noises intensely. These memories are also characterized by the presence of “idiosyncratic details” that seem to be irrelevant to the overall scene.

More details, but not necessarily accurate details

Because we can easily recall a lot of details about the event, we believe those details accurately reflect what happened. But it turns out that the durability and the vividness of these memories are actually more reliable than their accuracy. In other words, although we feel like we remember exactly where we were and what we were doing, the evidence suggests that our confidence may be misplaced.

Have you ever disagreed with a spouse or a sibling about what actually happened at an event you both attended? You might realize that our memories are not a perfect reproduction of what occurred in the past. Instead, psychologists describe memories as being reconstructions of the past. Memories are based, in part, on what actually happened (obviously), but are also influenced by our current thoughts and emotions and our reasons for remembering.

You don’t remember events exactly as they happened

All memories tend to lose detail over time and we sometimes confuse details from one event with those from another. This is also true of flashbulb memories. We are just as prone to forgetting and, more interestingly, potentially more vulnerable to mis-remembering, flashbulb memories than other autobiographical memories. Because we frequently think about and talk about our flashbulb memories, we sometimes add details from other events or incorporate details suggested by others. By doing so, we shape our memories into a coherent, interesting story to share.

Media coverage contributes, in part, to this phenomenon. Repeatedly viewing footage that was only available later can sometimes lead to mistakenly remembering that you saw those images at the time of the event. The media can also serve as a cue to think about or talk about these memories, enhancing their accessibility and vividness.

So, although we have a subjective feeling of remembering these events “exactly” as they occurred, this is typically not the case. When people are asked to record their memories, these objective reports for flashbulb memories include errors of omission and commission to the same degree as other autobiographical memories from the same time.

Why, then, do we feel like we remember exactly where we were and what we were doing when we learned of an important event? Because doing so demonstrates to ourselves and to others what we believe to be important.

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Microsoft has announced its intention to hire more autistic people – not as a charitable enterprise but because, as corporate vice-president Mary Ellen Smith said: “People with autism bring strengths that we need at Microsoft.” Employing autistic people makes good business sense.

Microsoft is not the only firm to reach this conclusion. More and more companies are beginning to seek employees from the pool of autistic talent. Specialisterne is a consultancy that recruits only autistic individuals. Originally based in Denmark it now operates in 12 countries worldwide and is currently working with Microsoft.

In recent years Vodafone and German software giant SAP have also launched recruitment drives to find more autistic employees, and to provide better support for them in the workplace. Both companies state that this is due to the competitive edge it gives, with SAP executives reporting increased productivity.

This is testament to the excellent work that many autistic people and their supporters have done to raise awareness of the strengths and abilities associated with autism, as well as the better-known difficulties with social communication and interaction. But what are these strengths?

Highlighting strengths not drawbacks

The three companies above might suggest that benefits come to those working in computing. Indeed Specialisterne has revealed that its autistic consultants find on average 10% more bugs than their non-autistic colleagues when checking software code for errors.

There is growing evidence to back up these observations. Studies of attention and perception among people with autism reveal that those with the condition see the world differently. For example, my colleagues and I have shown that autism is characterised by Increased Perceptual Capacity – the ability to process more information at any given time.

This can be problematic if the extra information results in altered sensitivities – such as finding bright lights painful, or having difficulty focusing on a conversation in a noisy room. But in other situations it can provide an increased ability to absorb and process useful information at an exceptional level of detail.

For example, in tasks that require you to find a target hidden among other elements, autistic people are faster and more accurate. They are also better at noticing both expected and unexpected things in their visual field. Autistic people also show excellent pattern recognition, a superior ability to identify and remember sounds and are much more likely to have perfect pitch.

This gives them skills to excel as artists, musicians and scientists. Perhaps controversially, these skills are also put to military use: the Israeli Defence Force has a specialist intelligence unit comprised exclusively of autistic analysts, whose skills are used to detect military threats.

Beyond stereotypes

Is this idea of the “autistic genius” who is more comfortable with computers than people a worrying throwback to old stereotypes? We should be careful not to regress to the Rain Man vision of autism, depicting autistic people as largely unable to function yet with an isolated area of genius. Such savants do exist, but they are rare (1-10% of the population), whereas the increased perceptual abilities discussed above are more common. While the latter are less extreme, they demonstrate that alongside the difficulties autistic people often have unique gifts.

Temple Grandin, an autistic author, self-advocate and professor agrees, arguing that: “the autistic brain is good at something and bad at something else”. She urges us to seek out autistic people’s skills, rather than fixating on shortcomings. There are many old jokes within the IT industry that the top programmers at leading firms are on the autistic spectrum – hidden away in solitary cubicles, coding for hours on end (for example Bill Gates is regularly diagnosed as autistic by the press).

But Grandin reminds us not to pigeonhole all people based on classic “autism skills”. There are many types of autistic brain: not only the pattern thinkers and mathematicians who will excel at programming but also visual thinkers who will be great graphic designers, artists such as Stephen Wiltshire and photographers, or verbal thinkers who would make excellent stage actors (including Darryl Hannah) or journalists.

Improving chances

Society’s understanding of this issue is improving, but there’s still much to be done. According to the National Autistic Society’s 2012 survey, only 15% of autistic adults in the UK are in full-time paid employment (compared to 31% for other disabilities), despite 61% of those who are unemployed saying they want to work.

What can we do to improve this? Microsoft’s announcement and others like it helps, but employers need to be better educated about the value autistic employees can bring. Businesses need to know about potential difficulties that autistic employees might experience, the simple adjustments that can accommodate them and the wide range of skills and interests that they can bring to the workplace. Lee Scott MP, the prime minister’s special needs envoy, is developing a scheme that will ask each MP to help find work for young autistic people in businesses in their constituencies.

We also need the education system to be better at equipping autistic people with the skills they need. On his blog, John Elder Robison, an autistic author and engineer, explains how the expectation of college graduation is harmful and believes we need to focus on making sure students, autistic and non-autistic alike, gain the skills they need rather than achieve a particular qualification. This leans towards more vocational programmes that capitalise on individuals’ special interests and abilities, helping shape those into employable skills.

The film X+Y is an example of what happens when talent and ability is identified early and fostered in the right way. Based on the real-life documentary (Beautiful Young Minds) about autistic mathematician Daniel Lightwing, the film tells his story from early childhood through his training to take part in the International Mathematics Olympiad. I won’t spoil the ending, but it’s definitely worth a watch.

We must also take care to value all autistic individuals, irrespective of whether they have a particular ability or not. As the extremely eloquent Ari Ne’eman, autistic campaigner and member of the US National Council on Disabilities, said: “People have worth regardless of whether they have special abilities. If society accepts us only because we can do cool things every so often, we’re not exactly accepted.”

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Music education in the western world often emphasizes musical literacy, the ability to read musical notation fluently. But this is not always an easy task – even for professional musicians. Which raises the question: Is there such a thing as musical dyslexia?

Dyslexia is a learning disability that occurs when the brain is unable to process written words, even when the person has had proper training in reading. Researchers debate the underlying causes and treatments, but the predominant theory is that people with dyslexia have a problem with phonological processing – the ability to see a symbol (a letter or a phoneme) and relate it to speech sounds. Dyslexia is difficult to diagnose, but it is thought to occur in up to 10% of the population.

In 2000, Neil Gordon, a retired pediatric neurologist, proposed the idea of musical dyslexia (dysmusia), based on growing evidence that the areas of the brain involved in reading music and text differed.

The idea that dyslexia could affect the reading of non-language symbols is not new. For instance, dyscalculia is the difficulty reading and understanding mathematical symbols. Recent research supports dyslexia and dyscalculia as separate conditions with unique causes (dyscalculia is thought to be caused by a deficit in spatial processing in the parietal lobe). If the brain processes words and mathematical symbols differently, why not musical symbols too?

Music’s written system

Western music, like language, has a highly evolved coding system. This allows it to be written down and transmitted from composer to performer. But music, unlike language, uses a spatial arrangement for pitch. The page is divided into staffs of five lines each. Basically, the higher a symbol is placed on the staff, the higher the pitch.

Unlike letters in text, pitches can be stacked, indicating simultaneous performance (chords). Music also uses a system of symbols to indicate how pitches should be played. Symbols can indicate duration (rhythm), volume (dynamics) and other performance cues. Music also utilizes written words to indicate both the expressive features of the music and the lyrics in vocal music. Lyrics may be in languages not spoken by the performer.

Due to differences in the physical features of the written systems, it makes sense that the brain would read music and text differently. This appears to be the case – at least to some extent.

Text and music reading in the brain

In the brain, reading music is a widespread, multi-modal activity, meaning that many different areas of the brain are involved at the same time. It includes motor, visual, auditory, audiovisual, somatosensory, parietal and frontal areas in both hemispheres and the cerebellum – making music reading truly a whole brain activity. With training, the neural network strengthens. Even reading a single pitch activates this widespread network in musicians. While text and music reading share some networks, they are largely independent. The pattern of activation for reading musical symbols and letters is different across the brain.

Brain damage, especially if it is widespread, as was the case with the composer Maurice Ravel, (perhaps best known for Boléro), will likely impair both text and music reading abilities. Ravel had a form of frontotemporal lobe dementia.

However, there have been cases where a more limited brain injury impaired reading of one coding system and spared the other.

Ian McDonald, a neurologist and amateur pianist, documented the loss and recovery of his own ability to read music after a stroke, though his ability to read text was unaffected. Oliver Sacks described the case of a professional pianist who, through a degenerative brain disease (Posterior Cortical Atrophy), first lost her ability to read music while retaining her text reading for many years. In another case, showing the opposite pattern, a musician lost his ability to read text, but retained his ability to read music.

Cases where music and language seem to be differently affected by brain damage have fascinated researchers for centuries. The earliest reported case of someone who was unable to speak, but retained his ability to sing, was in the 1745 article, On a Mute who Can Sing.

More recently, the Russian composer, Vissarion Shebalin, lost his language abilities after a severe stroke, but retained his ability to compose. Maintaining the ability to sing in the absence of language has led to the creation of a therapeutic treatment called Melodic Intonation Therapy that essentially replaces speech with song. This allows the patient to communicate verbally. These cases and many others demonstrate that music and language are to some extent separate neurological processes.

Differences in reading ability can occur even within musical notation. Cases have been reported where musicians have lost their ability to read pitch, but retained their ability to read rhythm, and vice versa. fMRI studies have confirmed that the brain processes pitch (spatial information) and rhythm (symbol recognition) differently.

Musical dyslexia

The research starts to imply how a specifically musical dyslexia could occur. This deficit may be centered on pitch or musical symbols or both. No conclusive case of musical dyslexia has yet been reported (though Hébert and colleagues have come close) and efforts to determine the effects of dyslexia on reading musical notation have been inconclusive.

Children in western cultures are taught to read text, but not always taught to read music. Even when they are, inabilities to read music are not generally treated as a serious concern. Many gifted musicians are able to function at a professional level purely learning music by ear. Among musicians, there is a wide range of music reading proficiencies. This is especially apparent with sight reading (the first performance of a notated piece). Identifying musical dyslexia could help explain why some musicians read well and others don’t.

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Sleep has profound importance in our lives, such that we spend a considerable proportion of our time engaging in it. Sleep enables the body, including the brain, to recover metabolically, but contemporary research has been moving to focus on the active rather than recuperative role that sleep has on our brain and behaviour.

Sleep is composed of several distinct stages. Two of these, slow-wave (or deep) and REM sleep, reflect very different patterns of brain activity, and have been related to different cognitive processes.

Slow-wave sleep is characterised by synchronised activity of neurons in the neo-cortex firing at a slow rate, between 0.5 and three times per second. The neo-cortex comprises the majority of the cerebral cortex in the brain which plays a role in memory, thought, language and consciousness. In contrast during REM sleep, when most of our dreaming happens, neuronal firing is rapid and synchronised at much higher frequencies, between 30 to 80 times per second.

Such patterns of brain activity during REM sleep are reminiscent of those observed during wakefulness, and for this reason REM sleep is often referred to as “paradoxical” sleep.

Cognitive functions

There is growing evidence that slow-wave sleep is related to the consolidation of memory and is involved in transferring information from the hippocampus, which encodes recent experiences, and forging long-term connections within the neo-cortex. REM sleep has been linked to processes involving abstraction and generalisation of experiences, resulting in creative discovery and improved problem solving.

Though there are substantial similarities between wakefulness and REM sleep, numerous studies have explored differences in the activity of brain regions between these states, with the cingulate cortex, hippocampus and amygdala more active during REM sleep than wakefulness. These regions are particularly interesting to cognitive neuroscientists because they are key areas involved in emotional regulation and emotional memory.

However, which sub-regions are active within these broader cortical and limbic areas – the pathways in the brain that produce these patterns of activation – and the precise function of the activity in these regions during REM sleep is currently under-described.

Cortical activity in rats

A new study published in Science Advances studied the physiology and functionality of REM sleep in a group of rats and provides insight into the cortical activity and the sub-cortical pathways that result in this activity. The level of detail of this study provides a major step forward for our understanding of the effect that REM sleep has on our brain and cognitive behaviour.

The authors studied groups of rats who were allowed to sleep, but prevented from entering REM sleep for three days. Six hours before assessment, half of the rats were allowed to sleep normally, and half continued to be deprived of REM sleep. The rats that were permitted to sleep normally then demonstrated raised levels of REM sleep within those six hours. This enabled a comparison of the effect of recent REM sleep between groups. An additional control group of rats were allowed to sleep normally throughout the study.

Gene expression analysis involves tracking the presence of particular mRNA or proteins that can be identified as the consequences of certain genes operating. The rats who underwent substantial REM sleep before testing were found to demonstrate greater expression of several genes that are associated with syntaptic plasticity (how quickly their synapses can adapt to changes in a local environment) and which affects the efficiency of neural transmission in the hippocampus.

In the neo-cortex, the gene expressions related to how well our synapses adapt also increased following REM sleep, but those related to neural transmission were reduced compared with the group that was prevented from REM sleep. So, the function of REM sleep appears to be due to changes in the way that neurons communicate. This is consistent with the view that REM sleep allows the brain’s memory processing systems to re-balance, which enables effective responses to experiences the next day.

Where in the brain?

In a further study, the same group determined the precise location of where these changes actually occur in the brain. In the neo-cortex, there was a general increase in plasticity throughout several areas, including sensorimotor regions that bring together sensory and motor functions. In the hippocampus, it was generally confined to the dentate gyrus, which is thought to contribute to forming new episodic memories among other things. REM sleep was also associated with reduced neuro-transmission throughout many regions of the neo-cortex, indicating that REM sleep likely results in a general weakening of the connections between synapses, which may enable brain networks to better learn from multiple experiences rather than be affected only by single instances.

The final studies the group conducted determined the source of the cortical changes in plasticity and neuro-transmission during REM sleep. By tracking signal transmission between different brain areas together with chemical lesioning (in which brain areas are temporarily inactivated), they identified two further areas called the claustrum and the supramammillary nucleus as having key roles during REM sleep.

These two areas have been identified as involved in integrating emotion and memory. The claustrum is a very thin layer of neurons that are found underneath the inner neo-cortex. It is known to link to and from very many regions of this part of the brain. As such, the claustrum has been implicated in integrating stimuli from several senses and is involved in linking areas involved in emotional processing and attention.

The supramammillary nucleus, within the hippocampus, is also known to interconnect to multiple areas of the brain, several of which are associated with emotional processing.

The implications of this work provide converging evidence that REM sleep modulates activation and synaptic processing in areas of the brain that contribute to the processing of emotion. This is also consistent with previously untested accounts that suggest REM sleep is important for encoding memories (but without their emotional content). While the role of dreaming during REM sleep is still yet to be linked to observed effects from neuro-chemicals in the brain, understanding what is happening in our brains when we dream could yet prove to be key to processing of emotion and memory.

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