Why you can live a normal life with half a brain

A few extreme cases show that people can be missing large chunks of their brains with no significant ill-effect – why? Tom Stafford explains what it tells us about the true nature of our grey matter.

How much of our brain do we actually need? A number of stories have appeared in the news in recent months about people with chunks of their brains missing or damaged. These cases tell a story about the mind that goes deeper than their initial shock factor. It isn’t just that we don’t understand how the brain works, but that we may be thinking about it in the entirely wrong way.

Earlier this year, a case was reported of a woman who is missing her cerebellum, a distinct structure found at the back of the brain. By some estimates the human cerebellum contains half the brain cells you have. This isn’t just brain damage – the whole structure is absent. Yet this woman lives a normal life; she graduated from school, got married and had a kid following an uneventful pregnancy and birth. A pretty standard biography for a 24-year-old.

The woman wasn’t completely unaffected – she had suffered from uncertain, clumsy, movements her whole life. But the surprise is how she moves at all, missing a part of the brain that is so fundamental it evolved with the first vertebrates. The sharks that swam when dinosaurs walked the Earth had cerebellums.

This case points to a sad fact about brain science. We don’t often shout about it, but there are large gaps in even our basic understanding of the brain. We can’t agree on the function of even some of the most important brain regions, such as the cerebellum. Rare cases such as this show up that ignorance. Every so often someone walks into a hospital and their brain scan reveals the startling differences we can have inside our heads. Startling differences which may have only small observable effects on our behaviour.

Part of the problem may be our way of thinking. It is natural to see the brain as a piece of naturally selected technology, and in human technology there is often a one-to-one mapping between structure and function. If I have a toaster, the heat is provided by the heating element, the time is controlled by the timer and the popping up is driven by a spring. The case of the missing cerebellum reveals there is no such simple scheme for the brain. Although we love to talk about the brain region for vision, for hunger or for love, there are no such brain regions, because the brain isn’t technology where any function is governed by just one part.

Take another recent case, that of a man who was found to have a tapeworm in his brain. Over four years it burrowed “from one side to the other“, causing a variety of problems such as seizures, memory problems and weird smell sensations. Sounds to me like he got off lightly for having a living thing move through his brain. If the brain worked like most designed technology this wouldn’t be possible. If a worm burrowed from one side of your phone to the other, the gadget would die. Indeed, when an early electromechanical computer malfunctioned in the 1940s, an investigation revealed the problem: a moth trapped in a relay – the first actual case of a computer bug being found.

Part of the explanation for the brain’s apparent resilience is its ‘plasticity’ – an ability to adapt its structure based on experience. But another clue comes from a concept advocated by Nobel Prize-winning neuroscientist Gerald Edelman. He noticed that biological functions are often supported by multiple structures – single physical features are coded for by multiple genes, for example, so that knocking out any single gene can’t prevent that feature from developing apparently normally. He called the ability of multiple different structures to support a single function ‘degeneracy’.

And so it is with the brain. The important functions our brain carries out are not farmed out to single distinct brain regions, but instead supported by multiple regions, often in similar but slightly different ways. If one structure breaks down, the others can pick up the slack.

This helps explain why cognitive neuroscientists have such problems working out what different brain regions do. If you try and understand brain areas using a simple one-function-per-region and one-region-per-function rule you’ll never be able to design the experiments needed to unpick the degenerate tangle of structure and function.

The cerebellum is most famous for controlling precise movements, but other areas of the brain such as the basal ganglia and the motor cortex are also intimately involved in moving our bodies. Asking what unique thing each area does may be the wrong question, when they are all contributing to the same thing. Memory is another example of an essential biological function which seems to be supported by multiple brain systems. If you bump into someone you’ve met once before, you might remember that they have a reputation for being nice, remember a specific incident of them being nice, or just retrieve a vague positive feeling about them – all forms of memory which tell you to trust this person, and all supported by different brain areas doing the same job in a slightly different way.

Edelman and his colleague, Joseph Gally, called degeneracy a “ubiquitous biological property … a feature of complexity”, claiming it was an inevitable outcome of natural selection. It explains both why unusual brain conditions are not as catastrophic as they might be, and also why scientists find the brain so confounding to try and understand.

My BBC Future column from before Christmas. The original is here. Thanks to everyone on twitter who chipped in on the plural of cerebellum

Cushing’s abandoned brains

I’ve just found a great short documentary about the abandoned brain collection of pioneering neurosurgeon Harvey Cushing.

The video describes how Cushing’s archives, which genuinely involved hundreds of brains in jars, as well as rare slides and photos of the early days of brain surgery, were rediscovered in the basement of Yale University and restored to public view.

Cushing is often called the ‘father of modern neurosurgery’ and spent a lot of time studying brain pathology by archiving and classifying tumours, bleeds and post-mortem brains in jars for others to learn from, as well as creating amazing medical illustrations – including the one below.
 


This archive became less necessary as technology moved on and the brain collection was moved into the basement below the medical school dormitories at Yale University and forgotten about.

The archives were eventually found again and restored as the Cushing Center which is now open to the public.

While the video focuses on the brains, Morbid Anatomy put some of the photos of patients from the archive online which are quite striking in themselves.
 

Link to Cushing’s Brains documentary on YouTube.
Link to Morbid Anatomy gallery of Cushing’s photos.

Beautiful online neuroscience learning

The Fundamentals of Neuroscience is a free online course from Harvard and it looks wonderful – thanks to them employing animators, digital artists and scientists to lift the course above the usual read and repeat learning.

The course is already underway but you can register and start learning until mid-December and you can watch any of the previews to get a feel for what’s being taught.

As you can see from the syllabus it focuses on the fairly low-level operation of the biology of brain but it’s all essential knowledge that will undoubtedly be a joy to encounter or re-acquaint yourself with.

You need to register to access the full content but there’s plenty of trailers online. Great stuff.
 

Link to ‘Fundamentals of Neuroscience’ course.

A Rush of Blood to the Brain

An article from Culture, Medicine, and Psychiatry that discusses the concept of ‘moral disability’ and brain trauma in Victorian times includes a fascinating section on what was presumably thought to be the science of ‘knocking some sense into the brain’.

The piece is by medical historian Brandy Shillace who researches Victorian scientific ideas and how they affected society.

Sadly, the article is locked (quite rightly, humanities can kill if not used correctly) but this is the key section:

While eighteenth-century French philosopher François Bichat had suggested that a blow suffered to one side of the head might restore the good senses of the disordered side, Wigan’s work suggested that “where such mental derangement depends on inflammation, fever, impoverished or diseased blood, or other manifestly bodily disease,” it could be cured by actively seeking and rooting out the source, by trephining the brain or otherwise subduing the offending hemisphere… The Lancet was replete with unusual cases of brain trauma and its curious results, many that seemed to support Wigan in his assumptions about physical trauma, variously applied.

I performed a survey from 1839 to 1858 and discovered a case of brain trauma in numerous issues, eight of which were particularly revelatory of the unusual nature of the brain and its hemispheres. The 1843 account of Dr. Peter S. Evans, “Derangement of the Brain by a Sudden Shock and Its Recovery,” claims that a boy was beaten into idiocy, and then beaten out of it again (regaining his full senses after being whipped by a cart driver). One of Wigan’s cases describes a young gentleman in a “paroxysm of maniacal delirium” who shot himself sane.

Not recommended.
 

Link to locked article in Culture, Medicine, and Psychiatry

Agents, social encounters and hallucinated voices

I’ve written a piece for the new PLOS Neuro Community about how the social aspects of hallucinated voices tend to be ignored and how we might go about making it more central in psychology and neuroscience.

It came about because the PLOS Neuro Community have asked authors of popular papers to write a more gentle introduction to the topic, so the piece is based on a PLOS Biology paper I wrote last year.

I’ve met a lot of people who hear hallucinated voices and I have always been struck by the number of people who feel accompanied by them, as if they were distinct and distinguishable personalities. Some experience their hallucinated entourage as hecklers or domineering bullies, some as curious and opaque narrators, others as helpful guardians, but most of the time, the voice hearer feels they share a relationship with a series of internal vocal individuals.

The piece discusses psychology and neuroscience but in the post, I also mention some work I’ve been doing with philosopher of mind Sam Wilkinson. As luck would have it, Sam just published a post about what we’re working on, on the excellent Imperfect Cognitions blog.

It looks at hallucinated voices and the representation of agency and agents. If you’re not used to these terms they can be slightly opaque but they refer to how the mind and brain represents autonomous individuals – be they human, animal, presumed or imaginary – and how that might relate to the experience of having hallucinated voices.
 

Link to A Social Visit with Hallucinated Voices.
Link to The Representation of Agents in Auditory Verbal Hallucinations.

A torrent of accidental poems

CC Licensed photo by Flickr user Jonathan Reyes. Click for source.Neurology journal Neurocase has an interesting study of a women who started compulsively writing poetry after having brief epileptic amnesia treated with the anti-seizure drug lamotrigine.

A 76-year-old woman reported having a poor memory and short periods of disorientation and was eventually diagnosed with transient epileptic amnesia – brief recurrent seizures that lead to short periods where affected people can’t lay down new memories.

Several months after starting lamotrigine [a common and widely used anti-seizure drug], the patient suddenly began to write original verse. Whereas poetry had never previously been among her pastimes, she now produced copious short poems (around 10–15 each day) on quotidian topics such as housework or about the act of versifying itself and sometimes expressing her opinions or regret about past events. These poems often had a wistful or pessimistic nature but did not have a moral or religious focus. Her husband characterized them as “doggerel” because they were generally rhyming and often featured puns and other wordplay.

My poems roams,
They has no homes
Yours’, also, tours,
And never moors.

Why tie them up to pier or quay?
Better far, share them with me.

Prose – now, that’s a different matter.
Rather more than just a natter.
Prose is earnest, prose is serious
Prose is lordly and imperious
Prose tells you, loud, clear, that
Life – life is dear.

This versifying had a compulsive quality: she spent several hours per day writing poetry and became irritated if attempts were made to disengage her. However, she appeared to derive pleasure from the activity and there was no evidence of associated distress. She did not produce prose passages, diaries, or other examples of hypergraphia, nor did she develop new interests in other “creative media,” such as visual arts or music.

When reassessed 6 months after the onset of versifying this apparent compulsion had diminished, but she continued to produce occasional poems. She had also developed a more general fondness for wordplay, frequently using puns in speech, making humorous word associations, and identifying word patterns in everyday objects such as car license plates. Throughout this period there were no associated mood symptoms, features of a thought disorder, or other changes in her behavior or cognition to suggest hypomania or another generalized neuropsychiatric disturbance.

The article mentions the exclusion of hypomania and thought disorder because these are two other phenomena that appear as compulsive rhyming or punning in speech.

The article also mentions some similarities between the compulsive poem writing and hypergraphia – compulsive and copious writing that is a well-known although not particularly common symptom of epilepsy.

The difference in this case, however, is that hypergraphia often appears as meaningless, rambling or disorganised, and this particular patient produced competent, if not particularly high quality poems.

One of the most interesting implications of these cases is that rhyming, punning and poetic speech, which we normally think of as something that needs specific conscious effort and attention, can appear spontaneously to the point of overwhelming our normal forms of communication.
 

Link to open-access scientific article.
Link to DOI of same.

How to speak the language of thought

We are now beginning to crack the brain’s code, which allows us to answer such bizarre questions as “what is the speed of thought?”

When he was asked, as a joke, to explain how the mind works in five words, cognitive scientist Steven Pinker didn’t hesitate. “Brain cells fire in patterns”, he replied. It’s a good effort, but all it really does is replace one enigma with another mystery.

It’s long been known that brain cells communicate by firing electrical signals to each other, and we now have myriad technologies for recording their patterns of activity – from electrodes in the brain or on the scalp, to functional magnetic resonance scanners that can detect changes in blood oxygenation. But, having gathered these data, the meaning of these patterns is still an enduring mystery. They seem to dance to a tune we can’t hear, led by rules we don’t know.

Neuroscientists speak of the neural code, and have made some progress in cracking that code. They are figuring out some basic rules, such as when cells in specific parts of the brain are likely to light up depending on the task at hand. Progress has been slow, but in the last decade various research teams around the world have been pursuing a far more ambitious project. We may never be able to see the complete code book, they realised, but by trying to write our own entries, we can begin to pick apart the ways that different patterns correspond to different actions.

Albert Lee and Matthew Wilson, at the Massachusetts Institute of Technology (MIT) first helped to set out the principles in 2002. It progresses like this. First, we record from the brain of a rat – one of our closer relatives, in the grand tree of life – as it runs a maze. Studying the whole brain would be too ambitious, so we can focus our recording on an area known as the hippocampus, known to be important for navigation and memory. If you’ve heard of this area before it is probably because of a famous result which showed that London taxi drivers developed larger hippocampi the longer they had spent navigating the streets of England’s sprawling capital.

While the rat runs the maze we record where it is, and simultaneously how the cells in the hippocampus are firing. The cell firing patterns are thrown into a mathematical algorithm which finds the pattern that best matches each bit of the maze. The language of the cells is no less complex, but now we have a Rosetta Stone against which we can decode it. We then test the algorithm by feeding it freshly recorded patterns, to see if it correctly predicts where the rat was at the point that pattern was recorded.

It doesn’t allow us to completely crack the code, because we still don’t know all the rules, and it can’t help us read the patterns which aren’t from this bit of the brain or which aren’t about maze running, but it is still a powerful tool.  For instance, using this technique, the team was able to show that the specific sequence of cell firing repeated in the brain of the rat when it slept after running the maze (and, as a crucial comparison, not in the sleep it had enjoyed before it had run the maze).

Fascinatingly, the sequence repeated faster during sleep around 20 times faster. This meant that the rat could run the maze in their sleeping minds in a fraction of the time it took them in real life. This could be related to the mnemonic function of sleep; by replaying the memory, it might have helped the rat to consolidate its learning. And the fact that the replay was accelerated might give us a glimpse of the activity that lies behind sudden insights, or experiences where our life “flashes before our eyes”; when not restrained, our thoughts really can retrace familiar paths in “fast forward”. Subsequent work has shown that these maze patterns can run backwards as well as forwards  – suggesting that the rats can imagine a goal, like the end of the maze, and work their way back from that to the point where they are.

One application of techniques like these, which are equal parts highly specialised measurement systems and fiercely complicated algorithms, has been to decode the brain activity in patients who are locked in or in a vegetative state. These patients can’t move any of their muscles, and yet they may still be mentally aware and able to hear people talking to them in the same room. First, the doctors ask the patients to imagine activities which are known to active specific brain regions – such as the hippocampus. The data is then decoded so that you know which brain activity corresponds to certain ideas. During future brain scans, the patients can then re-imagine the same activities to answer basic questions. For instance, they might be told to imagine playing tennis to answer yes and walking around their house to answer no – the first form of communication since their injury.

There are other applications, both theoretical science, to probe the inner workings of our minds, and practical domains such as brain-computer interfaces. If, in the future, a paraplegic wants to control a robot arm, or even another person, via a brain interface, then it will rely on the same techniques to decode information and translate it into action. Now the principles have been shown to work, the potential is staggering.

If you have an everyday psychological phenomenon you’d like to see written about in these columns please get in touch @tomstafford or ideas@idiolect.org.uk

This is my BBC Future column from monday. The original is here