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  Unnecessary-for-immediate-survival brain operations like having coherent thoughts are sacrificed in order for the brain to be able to maintain vital functions like respiration during a drop in glucose, electrolytes, or water. Confusion and hallucinations are also warnings from our brain that we are dangerously close to doing damage to our bodies. The next step is passing out. This is the brain’s last-ditch way of protecting our bodies from exercising to death.

  It doesn’t always work. Every year several participants in marathons die because they inadvertently pushed their brains and bodies beyond certain critical limits. The brain will keep trying to consume its disproportionate share of your body’s energy. That’s why when your body runs out of energy you become a drooling zombie.

  Now imagine that running yourself to death in a marathon is a compressed version of your entire life.

  During the marathon, as you approach the limits of your body’s capacity to withstand stress, your brain will keep giving you warnings. Your muscles will feel fatigued, and you will start to have an overwhelming urge to stop. You may become disoriented and have momentary lapses in awareness.

  Some people can override these warnings and push themselves past the point of no return. Over the long term in a less intense, but no less insidious way, our brains are constantly warning us that we work far too much. On the time-scale of a lifetime, constant stress from overwork raises your risk of depression, heart-disease, stroke, and certain kinds of cancer. It’s a long, horrible list.

  Yet we feel obliged to risk our long-term health in order to work extremely hard at jobs we don’t particularly enjoy in order to buy things we don’t particularly want. This is otherwise known as free-market capitalism. According to politicians, CEOs, and bankers, this is also supposedly the highest form of social organization that human beings have attained.

  Few people fear being overweight as much as they fear terrorism, even though statistically being obese is much more of a threat to your life than terrorism. We do not know how much stress and overwork contribute to shortened life-spans. But we do know that obesity and sitting all day at your desk with a low level of constant stress are related. If you knew being idle (preferably while lying down on a blanket under a tree with a nice bottle of wine) for more hours of the day could add years to your life, what would you do?

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  The amazing thing about the default mode network (and the point of this book) is that its activity increases when we are doing nothing. What exactly does this mean? From the perspective of a brain imaging scientist using fMRI, it means that activity in this network spikes when subjects are just lying in a scanner doing nothing.

  More blood is delivering oxygen to the default mode network. More glucose and other brain metabolites are being consumed by this network. And the activity in each region of the network becomes correlated. Scientists can measure how well information is flowing in your default mode network using what’s called “graph theory.”

  Graph theory is a branch of mathematics that was invented in the 18th century. Recently, it has been remarkably useful in analyzing all kinds of complex networks, especially the brain.

  Networks are made up of nodes. The nodes are connected by things called edges, which are just abstract (or physical) lines drawn between nodes. An edge between two nodes means that there is a relationship between the nodes—i.e., information can flow between these nodes. Sometimes, information can only flow in one direction. This is called a directed edge. In other cases information can flow back and forth between nodes. This is called a non-directed edge. The really useful thing about graph theory is that it can be used to study things as different as air traffic, the internet, and social networks. When parts of a system form a complex network, what matters more than their actual microscopic structure is the relationship among the parts.

  In the brain, these nodes are made of anatomically distinct structures. The nodes are connected by edges which take the form of axons. Areas of the brain that are physically connected are called “structural networks.” Just as the body has different parts—the heart or lungs, for example—so too does the brain. These different brain parts are connected via alien-finger-like structures called fiber pathways. The brain’s structural network is dense with local clusters that are interconnected to each other and to the global network. You are likely familiar with well-known brain regions like the prefrontal cortex.

  We can think of nodes as airports, and we all know hub airports: Chicago, Heathrow, or Frankfurt. These airports are huge compared to regional airports and receive much more air traffic than smaller airports. Have you ever been able to fly direct from Portland, Oregon to Columbus, Ohio? Usually you would have to fly over Chicago (or maybe even to some out-of-the-way hub like Atlanta).

  The brain works the same way. There are certain structures in the brain that receive many more connections than other parts. These are the hubs. When you are idle your “brain hubs” light up with activity. More blood carrying oxygen and sugar flow to the hubs in your default mode network when you relax and start daydreaming.

  Over the last twenty years, technologies like the MRI and PET (Positron Emission Tomography) have allowed scientists to look inside the living brain and take snapshots of its activity or measure how much energy certain brain parts are consuming while subjects perform experiments. We now know that each anatomically distinct brain structure is specialized to do different things.

  Consider the heart. It is a specialized body part that circulates blood. Within the heart there are smaller parts and each performs a more specific function. For example, the left atrium pumps oxygenated blood to the aorta, which pumps it out to the rest of the body.

  Similarly, in the brain, the prefrontal cortex is involved in so-called “high-level” cognition like reasoning, short-term memory, controlling your emotions, planning activities, and bringing relevant memories to consciousness. Another brain region called the hippocampus (parts of which are active during rest) is responsible for creating long term memories and storing them in another part of your brain called the neocortex.

  The prefrontal cortex decides when it is relevant to recall certain memories or information stored in your neocortex. Each of these regions can again be subdivided into smaller sub-regions which, in concert, perform larger tasks like “remember the name of that woman who also has a child in my son’s daycare and who I see every day and who knows my name.”

  For example, let’s say you meet your Aunt Lisa. You have stored in your neocortex all kinds of information about your Aunt Lisa. This information is distributed throughout the cortex and has to be reassembled when you recall it. When you meet her, you remember that she has Basenjis, she lives in Milwaukee, and she is married to your Uncle Jim. Your prefrontal cortex helps bring all this information into your awareness because it’s suddenly relevant when you’re talking to your Aunt Lisa.

  Conversely, any new information that you get from Aunt Lisa, including the current episode during which you met her, goes from your awareness (which involves many parts of the brain) to your hippocampus. Then if you get a good night’s sleep, relax for a while, or even take a nap, the hippocampus more or less writes these new memories to your neocortex, which houses your long-term memories. This is called memory consolidation. It is especially important when you are learning new ideas or skills. So the best thing to do after learning new information is to take nap, or at least be idle.

  The prefrontal cortex, the hippocampus, and parts of the neocortex have to talk to each other in order to accomplish all of this. One of the ways in which neurons and brain regions send and receive information is through synchronization of their oscillatory electrical activity. In ways we do not fully understand, when information needs to travel between nodes, this information gets coded into different frequencies which then ride on top of each other like ocean waves.

  High frequency waves can only travel short distances, but low frequency can travel much farther. Thus, it appears that informati
on coded in higher frequencies “rides” on top of lower frequencies, which can carry the information to distant brain regions. A fascinating example of perceiving far-traveling, ultra-low frequency waves was when the elephants and other animals in Thailand reacted to the approaching tsunami in 2004. Hours before any humans noticed the ultra-low frequency vibrations of the giant wave, the elephants could feel it and they headed to the hills well in advance of the destructive wave. This is because elephants can hear and feel frequencies far below the human threshold. These low frequency sound waves can travel hundreds of miles.

  Human neurons typically oscillate between 0.5 Hertz and upwards of one hundred Hz. However, it seems that most of our brain’s activity occurs at frequencies between one and forty Hz. The dominant frequency is called “alpha” which is around ten Hz. In the brain’s networks, the node receiving information needs to be oscillating in at least partial synchrony with the node sending the information.

  For example, when the prefrontal cortex needs to retrieve some associations from semantic memory, it will instantaneously synchronize its oscillations with parts of the temporal lobe, the place which stores the meanings of words. How this synchronization is achieved is still a mystery.

  The precise timing and spatial extent of this synchronization forms what’s known as the “neural code.” This is the brain’s own secret language. The holy grail of neuroscience is to crack the neural code which uses electrical and chemical signals in complex patterns that allow us to speak, read, think, remember, walk, become authors, make babies, and of course be idle.

  When anatomically distinct regions of the brain collaborate, as during Aunt Lisa’s visit, they temporarily form “functional networks.” These networks are functional in the sense that they are only formed in order to accomplish a certain task, such as to store some new factoid from Aunt Lisa. These networks can be short-lived, only lasting a few hundred milliseconds. One unresolved question in neuroscience is whether or not temporary functional networks can alter their underlying structural networks. In other words, if air traffic going to and from Bozeman, Montana were to increase beyond this airport’s capacity, would the city expand the airport, which might lead to even more air traffic?

  There is evidence of large scale plasticity in musicians who, compared to non-musicians, have much larger neural structures that represent their hands and fingers in the motor cortex. But presumably these changes take place over many years of training. The same is true of bilinguals: they have extra neural structures for languages in the temporal regions of the brain. London cabbies have famously large hippocampuses, specifically in the regions that help us navigate and remember spatial locations. It’s as if the brain decided to expand the airports in these areas to allow for the increased demand in traffic. It’s unknown how fast this type of structural change can happen in the brain. What we do know now is that brain plasticity is possible throughout our lifespan. So it truly is never too late to learn a new instrument, to learn a new language, or to radically change your life: your brain will change, too.

  As an adult, these changes may be more stressful, but they are often good for your brain’s long-term health. What’s also unknown is whether or not lazy people have larger or more active default mode networks. Would this be a cause or a result of being idle? If ten thousand hours of practice are needed to become an expert violinist, how many hours of being idle are required to become a master idler?

  The measure of how well the nodes in your default mode network are communicating is called “functional connectivity.” Functional connectivity is used to indicate how well your default mode network is working, and can provide information about your brain health in general, like the measure of how fast and safely air traffic travels between airports.

  When you are at rest, fMRI data can be used to see whether the nodes in your default mode network are active together. It is possible to see if oxygen in the blood at these regions increases or decreases at the same time. If you have a healthy brain and you are at rest, you will have high functional connectivity in your default mode network. As you age, if you don’t get enough sleep, if you have Alzheimer’s disease, or if you’ve had a stroke, the functional connectivity in your brain decreases, perhaps because of damage to nodes in the network.

  It follows that a lifetime of being super-productive and pointlessly-busy might also decrease the functional connectivity in your default mode network. Until Marcus Raichle discovered the default mode network, the only functional or structural networks neuroscientists thought were important were the ones they studied, which became active during tightly controlled experiments. This is because most brain scientists and psychologists assume that the brain’s primary purpose is to process external information.

  Until very recently, it has only been possible to study how humans respond to external stimulation. It wasn’t until we developed the technology to see inside the living brain and study its activity during idleness that we discovered that most of the brain’s activity is dedicated to internal operations.

  This does not in any way reduce the importance of what we’ve learned about how different systems in the brain respond to the environment. The motor system, for example, forms and executes commands to your nerves and muscles in your limbs to carry out actions, or to react to events in the world, such as an incoming tennis serve. This system has been studied for decades. But it turns out that when the motor system engages and tells your arm to swing a tennis racket after (or actually before) your visual system has reported an incoming serve, it might be only using a very tiny fraction of your brain’s total energy.

  While it is vitally important that neuroscience discovers what it can about the motor system, it may only be scratching the surface to study discrete areas of the brain while ignoring the “noise” of the resting brain. Noise, technically speaking, is some unwanted signal that usually interferes randomly with whatever signal we are studying. But the network that Raichle observed seemed to “deactivate” during active concentration on a stimulus and did not behave randomly. Nor did it interfere with signals of interest. It behaved perfectly regularly: when a subject begins actively thinking about something, this network deactivates.

  Why would a network in the brain decrease its activity during targeted mental tasks like remembering a list of words? Even more mysterious is the fact that the network decreases its activity regardless of the mental task in question. Looking at many different experimental conditions, the same thing happened: this network deactivated as soon as the subject began to perform an experimental task. Naturally, he wondered what happened to this network when people just lay there doing nothing. It turned out that the brain’s noise wasn’t “noise” at all.

  What Raichle found so striking was that many scientists still doubt that it is possible. They argue that it’s a measurement error, some technical problem, or an artifact of how fMRI data is analyzed. When subjects just lie in the MRI scanner and let their minds wander, the exact same network that deactivated during experimental tasks begins to hum with activity.

  Additionally, during mind-wandering the activity in the nodes in this network becomes highly correlated. This means that each part of the default mode network behaves the same way. Crucially, the default network that activates during idleness is almost perfectly “anti-correlated” with the network that activates during tasks that require your attention. You can probably guess what an anti-correlation is: the opposite of correlation. Something “X” which is anti-correlated with “Y” means that when the value of X goes up, the value of Y goes down, and vice versa.

  Using fMRI data, the signal that neuroscientists use to measure the activity of a certain brain region is called the Blood-Oxygen-Level-Dependent (BOLD) contrast. Without going into the complicated details, this signal tells you roughly how much blood and oxygen is flowing to an active brain region. When neurons increase their activity, they use more blood and oxygen (just like your muscles). A rise in the BOLD signal indicates an increase i
n brain activity.

  Even though the network your brain uses to actively pay attention only requires a small fraction of your brain’s total energy, when this attention network activates, your default mode network reduces its activity. This is what is meant by anti-correlated: when your attention network activates, your default mode deactivates. While you run around like a decapitated chicken in your daily life, trying to manage your schedule, trying to keep up with all your mobile devices, posting to your Twitter and Facebook accounts, receiving text messages, composing emails, and checking off to-do lists, you are suppressing the activity of perhaps the most important network in your brain.

  The two networks I have been describing are also referred to as the “task positive network” (TPN) and the “task negative network” (TNN). The task negative network is the same as the default mode network. The task positive network is the one that becomes active when you are frantically trying to manage your time.

  What all this means is that as you lie there letting your mind wander—or in the awkward language of neuroscientific writing, having Stimulus Independent Thoughts—your brain becomes more organized than if you are trying to concentrate on some task like color coding your Outlook calendar. Thus, when you space out, information begins to flow between the nodes in the default mode network. The activity in these regions and in the network as a whole increases. We shall see later why this might be so crucial to your creative mind, and to your health in general.

  * * *

  Where and what exactly is the default mode network? The default mode network arises from a set of posterior, medial, anterior medial, and lateral parietal brain regions. Posterior means “behind,” medial means “middle,” anterior medial means “middle front,” and lateral parietal means regions that are on both sides toward the top and back of your head. The specific regions that form the default mode network are called: medial prefrontal cortex, the anterior cingulate cortex, the precuneous, the hippocampus, and the lateral parietal cortex.