by Andrew Smart
What is important is to realize that these regions form nodes in the very large widespread network that is your default mode. These nodes are brain hubs. It is as if the default mode network comprises O’Hare, JFK, Heathrow, and Frankfurt airports. Together these nodes form the “epicenter” of your brain’s activity.
In the back of your brain (posterior) sits the precuneous. The precuneous is a hidden brain structure because it is close to the division between your brain’s hemispheres and parts of it are deep in your brain.
The precuneous has been difficult to study because of its location and because isolated injury to this region is rare. Therefore we cannot study patients who have had a stroke in the precuneous to find out what has been impaired. What we do know is that it is involved in spatial reasoning and consciousness. Interestingly, the precuneous also plays a role in self-processing operations like reflecting and maintaining a first-person perspective. Recent analysis using graph theory also indicates that the precuneous is a hub node, in addition to being part of the default mode network. Like O’Hare or Atlanta’s Hartsfield Airport, it has a lot of traffic.
During experimental tasks, or in real life when your attention is directed to a PowerPoint about risk management, the precuneous shows less activity. When you are stressing at work about the slip in the project schedule or doing “deep-dives” to find out why a product failed, this region deactivates. In other words: precuneous just doesn’t care.
However, the precuneous is also one of the regions that show the highest resting metabolic rate of any region in the brain. This means that at rest the precuneous starts devouring glucose like a crazed hummingbird. So if you can decouple from your “lean” workplace and start doing nothing, this hub in your default mode network revs up and starts redlining. Why is that important? The precuneous seems to be involved in self-reflection. One of the best ways to get to know yourself is to find a quiet or comfortably noisy place, stare at the sky, space out for a while and see what the precuneous gets up to.
Like the precuneous, the parietal cortex is also involved in representing you to yourself, sometimes called “meta-cognition.” The ability to think about this question and to have some kind of answer comes partly from our lateral parietal cortex. Life would be pretty meaningless if you lacked any awareness of yourself.
Coherent conscious representations of our own selves may be one of the unique traits of human cognition, along with language. Does a frog know he is a frog? Our own identities are of course based on these representations. Crucially, the lateral parietal cortex allows you to know whether you are a goth, a punk, a hipster, or a brain scientist. The lateral parietal cortex is also a node in the default network and thus its activity decreases during externally induced mental tasks. Like the precuneous, the lateral parietal cortex is also a hub node.
This may be why as you start daydreaming at work, when you should be tracking the hours spent on the latest rollout schedule for synergizing marketing plans across business units, your thoughts invariably drift toward questions like “how did a vibrant and wonderful person like me end up doing something so stupid, meaningless, soul-crushing, and mind-numbing?” Your default mode network knows you better than anyone—including your “getting things done” self.
The next part of the default mode network, called the anterior cingulate cortex (abbreviated as ACC), requires a short digression. You know already that your brain has two halves—called hemispheres. The hemispheres are connected via a fiber tract called the corpus callosum.
The corpus callosum allows information to flow between the two hemispheres. Sometimes, this fiber tract is cut surgically to prevent seizures in people with intractable epilepsy. Sitting like a collar wrapped around the corpus callosum is the anterior cingulate cortex. It is connected to the prefrontal cortex.
One of the anterior cingulate’s primary roles is to monitor your behavior together with feedback from your environment and to let you know when you’ve made a mistake. This is called “error detection.” In a similar way, when you are idle the anterior cingulate also seems to monitor your subconscious for potential solutions to problems.
When the ACC discovers some remotely associated concepts that might work together in a novel idea it directs your attention to this idea, thus boosting its activation so that the idea can enter your consciousness. As part of the default mode network, the ACC likes it when you are taking it easy and are in a positive mood. During idleness, it appears to be ready to help you find insightful solutions and come up with creative thoughts. When you are stressed out and worried about external concerns, the activity of the ACC decreases.
Journeying to the center of the brain, we find the hippocampus. This is one of the most studied brain regions because it is what allows us to form memories. In fact, there is an academic journal devoted entirely to the study of the hippocampus, unsurprisingly if unimaginatively called Hippocampus.
The hippocampus is a horseshoe-shaped structure deep in the middle of the brain. It has two halves which straddle the brain’s left and right hemispheres. As with all brain regions, the hippocampus seems to have a primary function—forming memories—but its sub-regions perform specialized tasks that range from learning how to navigate new spaces to creating new autobiographical memories.
When you lose parts of your hippocampus, you may not be able to create new memories. One of the reasons we know quite a lot about what the hippocampus does is from studying patients who have had parts of this region removed to stop intractable epilepsy from seizures that originate in this area. Often, when certain parts are removed, patients cannot form new memories.
So for example, when you meet a patient missing parts of the hippocampus he will not remember you the next time you meet, nor the time after that. He will not be able to recall ever meeting you before, no matter how many times you meet him. Parts of the hippocampus which seem to be involved in the creation and retrieval of autobiographical memories are also active in the default mode network. This is why when your mind begins to wander you may start to think about riding your bike as a child, that last presentation you gave, or the maniac who accosted you on the subway this morning.
All these memories must pass through the hippocampus when they are created and recreated when you recall them. What’s more, as you reflect back on your life, your default mode network seems especially good at using these memories to project forward into the future, creating images of yourself in future situations. The ability to reflect on your current situation, your past, and your future are all intimately related. People who have the luxury to spend time doing this by being idle tend to be more creative, and to have better mental health in general.
Moving toward the front of your head we arrive at the prefrontal cortex. Evolutionarily speaking, this is one of the last brain regions to evolve. Likewise, it is one of the final brain regions to mature during development. In fact, in males, the prefrontal cortex does not finish maturing until about age twenty-five. I mentioned above that the prefrontal cortex is responsible for skills like decision making, planning, impulse-control, and self-reflection—skills that many males under twenty-five tend to lack.
One of the major roles of the prefrontal cortex in your brain’s cognitive life is to make information in your brain available for manipulation and action—i.e., when information arrives in your prefrontal cortex you are likely to be aware of it. The prefrontal cortex is therefore considered necessary but not sufficient for consciousness.
The prefrontal cortex is not the only source of consciousness because many brain areas have to be ignited in order for you to become aware of something. However, it seems that the prefrontal cortex must be involved for you to have any sort of meaningful human-like experience with data.
Once you have a piece of information in your awareness you can do stuff with the information—e.g., think about it, make a decision, or let it simply pass from awareness back to your unconscious, such as in meditation. The amount of information you can hold in
awareness at any moment also depends on how well your prefrontal cortex is working. There seems to be a trade-off in the brain between being able to store a lot of information in your working memory and cognitive flexibility or creativity.
We often use an upside-down U-shaped curve to describe this—the bottom of one side of the U is total rigidity but very high storage, the other side of the U is complete flexibility but no storage. It turns out that being idle can help your brain naturally find a balance between these two extremes.
There are many parts to the prefrontal cortex. The region of the prefrontal cortex that is part of the default mode network is called the medial prefrontal cortex. It should not surprise you by now that this area also has a very high resting metabolic rate. There is also a high resting blood flow to the prefrontal cortex, which is critical for your conscious awareness and also for spontaneously-generated thoughts.
As part of the default mode network, the medial prefrontal cortex typically starts to shut down when you are an effective person: when you are going from your early morning gym session to the office, reviewing your PowerPoint slides, getting to the meeting, presenting the report, scarfing down take-away for lunch while checking your email, pounding another coffee, checking your calendar, putting little red dots on documents you’ve reviewed, answering calls, answering texts, scheduling appointments for the kids, planning to plan … ad infinitum.
It is only when your thoughts drift inward does the medial prefrontal cortex start to light up and talk to its partners in idleness—the precuneous, the anterior cingulate cortex, and the lateral parietal cortex. The medial prefrontal cortex also seems to be involved in a kind of surveillance of your brain’s internal operations, so that when you stop doing stuff and become idle this region of the brain can report what’s going on in the deepest recesses of your mind.
In a nutshell, when you are being lazy, a huge and widespread network in your brain forms and starts sending information back and forth between these regions. The butterflies only come out to play when all is still and quiet. Any sudden movements and they scatter.
The default mode network supports self-knowledge, autobiographical memories, social and emotional processes, and creativity. It persists as long as you can relax. Remember that when you are busy checking your to-do list, making sure you paid a bill, being productive at work, or improving your time management skills, the default mode network goes dormant.
The neurons in this network fire less, and therefore these brain areas need less glucose and less blood. You may have also noticed that each of the nodes in the default mode network is involved in thinking about yourself, reflecting on the past, and introspection. What’s more, these brain regions are all intricately involved in consciousness.
In addition to the disproportionate amount of energy the brain requires to maintain its ongoing activities, the structure of the brain also underlies its function of staying in a “metastable” state. “Metastable” here refers to the balance the brain must strike between stability and flexibility. In order to survive and reproduce, we need to be able to avoid predators, falling air-conditioners, and drivers talking on their cell phones.
However, it would be of little evolutionary advantage if every time we swerved to avoid a distracted driver, our personality disappeared or changed completely. In order to feel sane and make sense of the world, we need to perceive ourselves as continuous and coherent “selves.” How does the brain achieve this balance between a stable state that does not change and a highly sensitive and reactive flexibility that can react in milliseconds to sudden changes in the environment?
One possibility that neuroscientists are exploring is that the actual structure of the brain, how it is anatomically arranged and organized, actually establishes this metastability. The parts of the brain that make up the default mode network seem to be critical to the maintenance of an internal representation of ourselves.
We still do not fully understand the significance of the fact that the default mode network is formed from hub nodes. Because information is distributed throughout your brain, the hubs of your brain network are crucial to the efficient flow of this information to and from your consciousness. The hub structure of your brain’s network is what allows for memories to be almost instantaneously reconstructed as they enter your consciousness.
What appears to us as a single memory has to be reassembled from multiple brain regions every time we recall that memory. The short path-lengths through network hubs help this process to be so fast and automatic that we take it for granted.
In fact, recent evidence indicates that in neurodegenerative diseases such as Alzheimer’s, the default node network is disrupted and shows less activation. This could be one reason why it becomes so difficult for Alzheimer’s patients to recall memories: the information stored in their brains cannot make its way through the network.
Conversely, people with schizophrenia show hyperactivity and hyperconnectivity in their default mode networks. If your default mode network is too active and its nodes have too many connections, you can have problems differentiating between reality and fantasy. There is a long history to the study of the relationship between genius and madness. Many scholars have argued that there is a fine line between the two.
The fact that abnormal activity in the default mode network is involved in debilitating mental illness illustrates its critical nature. However, as with Alzheimer’s disease, the disruption in default mode network activity may be a symptom rather than a cause. Between these ends of the spectrum lies an optimal level of default mode network activity which enhances our feeling of well-being, our physical health, and our creativity.
Fortunately, the only way to attain this optimal level of default mode activity is to put your feet up, find a nice pillow, lie back, and let go of task-oriented activity. Looking at great art, listening to your favorite music, and doodling may help facilitate this process.
Unfortunately, laziness is so stigmatized in America that everyone knows what it means. The trick is learning to embrace, defend, and demand the right to laziness as a prerequisite for a good life and a healthy society, and also recognizing that the astounding insights that may occur from those who have a particularly robust default mode network are not anomalies, but the norm.
3
AHA! MOMENTS AND SELF-KNOWLEDGE
“On 15 April 1726 I paid a visit to Sir Isaac at his lodgings in Orbels buildings in Kensington, dined with him and spent the whole day with him alone … After dinner, the weather being warm, we went into the garden and drank tea, under the shade of some apple trees, only he and myself. Amidst other discourse, he told me, he was just in the same situation, as when formerly, the notion of gravitation came into his mind. It was occasion’d by the fall of an apple, as he sat in a contemplative mood.”
—William Stuckley
“A genius is someone who discovers that the stone that falls and the moon that doesn’t fall represent one and the same phenomenon.”
—Ernesto Sabato
Everyone knows the story of Newton’s apple. The theory of gravity is today the most basic scientific principle. However, in Newton’s day the idea of gravity as a fundamental force in the universe was a very strange one. In fact, to most people back then, invisible forces acting on things from a distance was either demonic or divine.
Newton himself had a difficult time accepting the reality of “action at a distance.” In fact he discouraged people from trying to figure out the true cause of gravity and to instead focus on the fact that his math and his experiments worked.
Using the lens of our contemporary time management culture, sitting in your garden in a “contemplative mood” is a complete waste of time. This (lack of) activity might indicate to some HR person that Newton was not necessarily a reliable employee. Did Newton have to add “5 pm: sit in garden, contemplate falling objects” to his to-do list? Does any reasonable person think that Sir Isaac Newton had a to-do list?
Newton was in fact
known for his obsessive work ethic. He could sit in his garden and do nothing because it would never have occurred to Newton that sitting in his garden contemplating was the same thing as wasting time.
Today we find popular magazines telling us we need to schedule “downtime” because the demands of corporate-controlled schedules are inhuman. Of course people are not explicit about the root of the problem, and we are advised to “schedule” the time off as long as it doesn’t conflict with our obligations. Downtime is actually advised as a way to optimize your productivity.
In the most literal sense, Newton was his own boss. He worked when he wanted to work, and he sat in his garden when it suited him. Naturally you will point out that this is impractical and unrealistic in the current economy. And I would say that we therefore deserve the paucity of intellectual dynamism that our economy compels.
Natural science before Newton was in a transformative phase. The period between the late 15th and 18th centuries is what many see as the crucial scientific revolution in human history. During time Copernicus, Kepler, Galileo, Brahe, and Newton each made enormous contributions to the advancement of the sciences. The 17th century especially saw an intellectual explosion that suddenly and massively increased our comprehension of the universe. Our knowledge about the natural world began expanding at an ever-accelerating rate that continues to this day. Human understanding of nature went from superstitious folk-belief to real science.
It was during this revolution that a scientific community came into being that published journals and started having meetings much like today’s scientific conferences. In the centuries since Newton, natural science has met with astonishing success. Typically we think of Newton seeing the apple fall as some kind of serendipitous moment in the history of science. Whatever the origin of the story really is, after seeing the apple fall and after working out his theory Newton wrote one of the most significant scientific publications in history: the Philosophiae naturalis principia mathematica, in which the formal theory of gravity is introduced.