My Plastic Brain Read online

  On the flipside, obesity has been shown to be particularly bad for the workings of the brain. Research by Alexis Stranahan, of Augusta University in Georgia, has found that, at least in mice, obesity switches on a sequence of events that turns the microglia—cells that gobble up anything foreign or unwanted in the brain—against connections between neighboring neurons.10 The result is that perfectly good connections start being gobbled up for no good reason. Stranahan, among others, is investigating whether this is why diabetes and obesity are so often linked to a decline in cognitive skills.

  A bad diet also seems to be particularly bad for the hippocampus, a key area for processing memory. This had led some researchers to conclude that a Western diet, high in fat and sugar, might make it more difficult for us to remember what we know about eating properly, which might make you more likely to choose a bad diet in the future—and so on and so on until the brain is as unhealthy as the rest of you.11

  Too little food is also bad for your brain, for more obvious reasons. Food is brain fuel—so if there's not enough in the tank, it makes sense that the machine won’t run very well. Interestingly, there seems to be evidence that getting “hangry” (feeling angry when you’re hungry) is a real thing, caused by the brain pulling out all the stops as it desperately tries to persuade us to seek out food. First, the hunger hormone ghrelin, from the gut, activates the amygdala, which makes us feel stressed, worried, or—in my household—downright furious about everything. Then the stress hormones cortisol and adrenaline are released, which prompts us to invest what energy we can muster into solving the problem.12

  Again, if you look at it through the handy lens of the caveperson, it makes a lot of sense: when food was too scarce to go around, only the feisty, “hangry” ones, who would club anyone who got between them and the last portion of mammoth, would have survived. “Hanger” is a key survival skill. (That's my excuse, and I’m sticking to it.)

  As for specific brain foods to eat, the short answer is, the good stuff. A diet that is high in trans fats and sugar has been linked to inflammation in the body—part of the immune response—and this has serious effects on the brain, putting it into a low-energy, hiding-away kind of sickness mode, which has recently been linked to a risk of depression.13 A diet high in fruit, vegetables, and oily fish does the opposite, keeping inflammation at a healthy level.

  The “good stuff” obviously contains a huge variety of nutrients, some of which have gained an almost mystical reputation as brain boosters. Of all of them, omega-3s and B vitamins and flavonoids seem to be among the most popularly touted as important. As with brain training, though, most of the advice out there in the public is irritatingly vague about what they actually do to support the brain, and how come most brains function fine even without sticking to an organic macrobiotic superfood diet.

  Omega-3s in particular have an unstoppable reputation for their brain-boosting skills, but what exactly they are doing in the brain is often conveniently skipped over. That's because, as with so much about the brain, most of what we know about what happens at the level of brain cells comes from animal studies; human studies haven’t quite gotten to the bottom of how adding omega-3 to the diet affects behavior and cognition just yet.

  Nevertheless, experiments on rats have shown that adding omega-3s to their diet does increase the levels of omega-3 fats in their brain tissues. Once inside the brain, omega-3s constitute an important building block of cell membranes, the barrier between one cell and another, which are built from two layers of fat molecules.

  Omega-3s are not the only fats involved in building membranes, and if your body can’t get enough of them then it will use other kinds of fats, like the saturated fats most of us consume plenty (too much) of. This explains why, if you don’t eat any omega-3s at all, your brain can still make cell membranes: that bit had always bugged me—if they are so crucial to membrane formation, how come so many people manage to have functioning brains with no omega-3s in their diet at all? The difference is that omega-3s and other polyunsaturated fats are longer in structure and more “kinked” than saturated fats, which makes the membranes more flexible and better able to transmit both electrical and chemical messages between them. Electrical signals need ion channels, or gaps, which form more readily in a flexible membrane, and chemical messages need fatty bubbles called vesicles to pass them across the membrane.

  In a petri dish, omega-3s have also been shown to increase the growth of connections to other neurons and to help newly grown neurons turn into mature ones—which makes me think that eating more of them is not a bad idea for anyone hoping to change their brain. The good news is that if you don’t get any omega-3s in your diet, your brain won’t grind to a total halt—it just won’t be firing on all cylinders and therefore won’t be in the best possible condition to learn and to change.

  With this in mind, I’d quite like to know if I have decent levels of omega-3s in my blood—or, more correctly, a healthy balance between them and their less healthy cousins, the omega-6s. There is some evidence that what matters isn’t the exact amount you have but the ratio between the two. Finding this out isn’t easy. Despite many unscientific websites telling me that lethargy and dry hair and skin are sure signs of an omega-3 deficiency, it all sounds a bit vague for my liking.

  Companies do exist that will test your omega-3 levels for a fee, but it seems like a bit of an extravagance when you already know whether or not you are getting the recommended one or two portions of oily fish a week, and there is no good evidence to date that adding more omega-3 on top of that makes any difference. As for whether supplements are as good as the real thing, the evidence suggests they are less good than eating fish—but if you hate oily fish then they are probably the next best thing. Studies of children, who are already malnourished and are lacking omega-3s, found that supplements improved reading, spelling, and school test results.14 Similarly, in studies of children with behavioral problems, supplements improved both their low levels of blood omega-3 and also reduced the number of tantrums and other problem behaviors. In adults, too, low omega-3 has been linked to depression, and, in experiments, supplementation seemed to reduce the reaction to stress. This effect isn’t restricted to the brain, by the way; it affects the whole body: reducing heart rate, blood pressure, and the stress-related hormones adrenaline and cortisol. This is further evidence that the brain and body are very much connected—which sounds obvious but is often forgotten in discussions about how you might change your brain.

  Incidentally, some researchers think that adding fish to the diet was what allowed our early ancestors in Africa to grow such large brains in the first place. According to estimates, they were almost certainly eating more fish than modern humans do, which is an interesting thought. Maybe they had brains that were better set up for learning than ours are?

  As for other brain-boosting foods, flavonoids—plant pigment chemicals found in berries, nuts, grapes, and cocoa and tea, among other plant-based foods—have some evidence to back up their reputation as superfoods. According to a recent review of what flavonoids are actually doing in the brain, it still isn’t clear exactly how they work; it may be that the flavonoids, or the smaller components that the body breaks them down into, are involved in important chemical reactions underlying brain function, or it might be that they simply improve blood circulation around the body, meaning that more of the good stuff gets to the brain.

  Either way, clinical trials in humans and rats have shown that flavonoid-rich diets help memory, learning, and cognitive function in general.15 The only bad news is that eating lots of chocolate—even the really dark, bitter stuff—isn’t enough to get your fill of flavonoids, and with the brain-stunting effects of too much fat and sugar, it's probably better to go with a mix of fruits and berries, with a bit of wine and chocolate on the side. Belt and braces, I always think.

  Then there are the B vitamins: B12 in particular is thought to play a role in protecting the myelin coatings on long-range brain wires, whic
h helps with any thinking that involves more than one brain area (most thinking). A team at Oxford University is currently researching whether B vitamin supplements help people with mild cognitive impairment, an early form of dementia, from progressing to full Alzheimer’s. It's still in the early stages, but it looks as if it might just help.

  All in all, then, it looks as if any serious attempt to get the best out of the brain is going to have to involve looking after the body through exercise, just the right amount of food, and a healthy, mixed diet. But that's not all. To complicate matters further, it seems there is another factor to consider in all of this, and it isn’t technically part of the human body at all. Research at University College Cork, in Ireland, has shown that there is a huge amount of communication between the gut and the brain, and that gut microbes have a big part to play in the contents of that conversation—whether the gut is healthy, stressed, or malnourished, and how the brain, and body, reacts.16

  A lot of the research on this has been done in mice because they can be kept in a sterile environment for their whole lives—and because they are bred from other “germ-free” mice, they don’t pick up any bacteria from their mother during birth either. This means that researchers can manipulate the microbes that the animals come into contact with and monitor the effects on their brain and behavior.

  The research showed that germ-free mice live longer, but they display abnormal social behavior and stress responses. Through some intriguing experiments, researchers found that adding gut bacteria from mice with normal stress response (via fecal transplant—you can learn how to do a fecal implant yourself online, but you probably won’t want to; suffice to say, you will need a new blender afterward) makes these stressed-out, germ-free mice behave normally, while giving normal mice the gut microbes of a stress-prone mouse does the opposite.

  It even works cross-species: infecting healthy mice with the gut flora of a depressed human made them act depressed in lab tests used as a proxy for depression in mice. Depression has a distinct microbial signature, the researchers say, and if you infect healthy mice with it, they start to behave accordingly. More than that, in human trials, adding a dose of a particular strain of a common bacterium (Bifidobacterium longum) to healthy volunteers not only reduced their levels of stress hormones and made them feel less stressed, but it also slightly improved their performance on memory and learning tests in the lab.17

  Over the past few years, it has emerged that there is seemingly nothing that gut bacteria can’t do for the brain. They regulate the birth of new neurons in the hippocampus, change levels of certain neurotransmitters, and also have a hand in the myelination process. None of this happens directly—as far as we know, there are no bacteria actually swimming about in the brain—but they seem to do something to start the chain of events that makes these things happen. One route by which they do this is via the vagus nerve, which links the gut, along with many other organs, to the brain.

  As well as giving the brain regular updates on the health of the organs, and on whether it's time to eat, the vagus nerve has been implicated in driving emotions too—particularly anxiety and fear. This is almost certainly where the expression “gut feeling” comes from; it seems that the gut, not the brain, is the first to sound the alarm in a threatening situation. In experiments where the stomach-to-brain section of the vagus nerve was severed in rats, they were far less naturally fearful in open arenas, where usually they would have kept a close watch on their surroundings.18

  When the researchers at University College Cork gave healthy mice a dose of Lactobacillus and Bifidobacteria, the mice showed changes in stress-related neurotransmitters in various parts of the brain, had lowered stress hormones, and were less anxious under stress. If the vagus nerve was cut, though, whatever message was passing along the nerve couldn’t get through, and their brains and behavior were unchanged. No one knows yet what kind of information the vagus nerve is sending from the gut—and its microbes—to the brain, but whatever it is, it seems to be important information for both body and mind.

  At the Society for Neuroscience conference in Chicago in October 2015, John Cryan, who leads the research in Cork, said that it raises the intriguing possibility that probiotics (living doses of friendly bacteria) or prebiotics (the right food to encourage specific bacteria) could help people with depression and autism, and, potentially, to improve brain function in general. The other option is to change diet—the specific bacteria that seem most beneficial to the brain are those that help break down dietary fiber, so making sure there is plenty of that alongside your superfoods is probably a good idea. According to Tim Spector, a professor of genetic epidemiology at King's College London and author of the 2015 book The Diet Myth: The Real Science behind What We Eat, variety is the key to keeping your gut microbes happy—although, he suggests having more celery, garlic, Belgian beer, and chocolate would be a good place to start. Spector's book aside, there is no specific dietary advice yet on how to give your gut bacteria the best environment in which to flourish. Nonetheless, the research into gut microbiomes does provide some intriguing hints that diet affects the way our brains work in ways that we haven’t considered, and that we might not be as much in control of our feelings and behavior as we might like.

  Finally, there's sleep, the lack of which is seriously bad for brain function. Even missing a couple of hours of sleep a night hammers your cognitive functioning and can leave you at risk of long-term bad health—even dementia. Science hasn’t quite worked out why sleep is important for the brain, but it is widely presumed to be crucial for maintenance, repair, and memory storage; according to Harvard's Sleep Lab, most adults need seven and a half to nine hours of sleep to do all of this.19 Any less than that and memory, mood, and reaction time all suffer. Only paying back the “sleep debt” with a good night's rest will return brain function to normal.

  There are exceptions, though. A rare mutation on the DEC2 gene allows some people to get by on four to six hours of sleep with no foggy head and, as far as researchers have yet been able to tell, no other effects on their health or lifespan. Only a few people with this mutation are known to science, and if you don’t wake up after a short night's sleep feeling fantastic then you probably don’t have it. Researchers are working toward one day giving other people the same benefits as the “short sleepers,” but so far there's no better advice than to go to bed when you’re tired and get up at the same time every day.

  What is most important to take away from all of this, though, is that while it's tempting to think of the brain as the driver of everything we do, think, and feel, there is a huge amount of evidence that the body has a big hand in it, too. This might actually be helpful to know when making any plan to keep the mind in tip-top condition. From what I’ve seen, it looks as if running the engines of the mind has a lot to do with running the body a little better. Whether there are any specific brain exercises that are needed on top of that…I guess we’ll see.

  NEUROPLASTICITY

  With so much uncertainty about pretty much everything so far, it seemed like a good idea to delve into the details of this thing called neuroplasticity to find out what it's all about.

  The good news is that whatever anyone thinks about the type of brain-training games and self-help books that invoke neuroplasticity, they didn’t just make it up. One thing that everyone can agree on is that if neuroplasticity isn’t happening inside your brain right now, you’re probably dead. It becomes problematic, however, when you try and pin down exactly what people mean when they say that something “promotes neuroplasticity” or “rewires the brain.”

  What we do know is that if you could look at your brain with a microscope right now (and we know this because scientists have done it in mice) you would see tiny bumps growing out of the branches of your neurons, feeling around like the tentacles of a curious octopus, sometimes connecting to a neighboring cell, and sometimes shrinking back again.

  This process of growth and retraction is happening all the t
ime, and while it might seem a bit wasteful to keep growing and shrinking all the time without much to show for it, it does allow the brain to stay primed and ready to make new connections when it needs to. Most of the time, at least in adults, there isn’t a great deal to see from one day to the next—the brain ticks along, making a few connections here, breaking a few there, with not much in the way of real, wholesale change. Only when something memorable happens, or you make an effort to learn something, do the new connections start to outnumber the old and the brain begins to change.

  This, of course, is the basic story that gets trotted out whenever people want to convince you that you can change your brain. If they really want to hammer the point home they’ll probably quote Canadian neuroscientist Donald Hebb who (almost) said that “neurons that fire together wire together,” back in 1949. (What he actually said was, “When an axon of cell A is near enough to excite a cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A's efficiency, as one of the cells firing B, is increased.”20 Stanford University neuroscientist Carla Shatz gets the credit for the snappier version.)

  The other line of evidence for brain change comes from brain-imaging studies in human volunteers, which have shown that when people learn a new skill, their brains change physically, growing a bigger area to take on the new work. Eleanor Maguire's studies with London taxi drivers are probably the best known. Over the past decade, she has shown that the posterior hippocampus, a part of the brain that is involved in spatial memory, gets larger in drivers who spend more time memorizing routes around London to pass “the Knowledge”—which tests their memory of 320 routes, 250,000 streets, and 20,000 landmarks in central London.21