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It also can lead to great creativity and solutions to problems that seemed unsolvable. Its discovery—a special brain network that supports a more fluid and nonlinear mode of thinking—was one of the biggest neuroscientific discoveries of the last twenty years.
The tendency for this system to take over is so powerful that its discoverer, Marcus Raichle, named it the default mode
The mind-wandering mode stands in stark contrast to the state you’re in when you’re intensely focused on a task such as doing your taxes, writing a report, or navigating through an unfamiliar city. This stay-on-task mode is the other dominant mode of attention, and it is responsible for so many high-level things we do that researchers have named it “the central executive.” These two brain states form a kind of yin-yang: When one is active, the other is not. During demanding tasks, the central executive kicks in. The more the mind-wandering network is suppressed, the greater the accuracy of
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My colleague Vinod Menon discovered that the mind-wandering mode is a network, because it is not localized to a specific region of the brain.
The mind-wandering mode works in opposition to the central executive mode: When one is activated, the other one is deactivated; if we’re in one mode, we’re not in the other.
In addition to the mind-wandering mode, the central executive, and the attentional filter, there’s a fourth component of the attentional system that allows us to switch between the mind-wandering mode and the central executive mode. This switch enables shifts from one task to another, such as when you’re talking to a friend at a party and your attention is suddenly shifted to that other conversation about the fire in the kitchen.
In a 2010 paper, Vinod Menon and I showed that the switch is controlled in a part of the brain called the insula, an important structure about an inch or so beneath the surface of where temporal lobes and frontal lobes join. Switching between two external objects involves the temporal-parietal junction.
The relationship between the central executive system and the mind-wandering system is like a see-saw, and the insula—the attentional switch—is like an adult holding one side down so that the other stays up in the air. This efficacy of the insula-cingulate network varies from person to person, in some functioning like a well-oiled switch, and in others like a rusty old gate.
Notice that the anterior cingulate extends from the orbital and prefrontal cortex in front (left on the drawing) to the supplementary motor area at the top. Its proximity to these areas is interesting because the orbital and prefrontal areas are responsible for things like planning, scheduling, and impulse control, and the supplementary motor area is responsible for initiating movement.
This four-circuit human attentional system evolved over tens of thousands of years—distinct brain networks that become more or less active depending on the situation—and it now lies at the center of our ability to organize information.
When the activation of a neural network is sufficiently high, relative to other neural activity that’s going on, it breaks into our attentional process, that is, it becomes captured by our conscious mind, our central executive, and we become aware of it.
Consciousness itself is not a thing, and it is not localizable in the brain. Rather, it’s simply the name we put to ideas and perceptions that enter the awareness of our central executive, a system of very limited capacity that can generally attend to a maximum of four or five things at a time.
The mind-wandering network recruits neurons within the prefrontal cortex (just behind your forehead and eyes) in addition to the cingulate (a couple of inches farther back), joining them to the hippocampus, the center of memory consolidation. It does this through the activity of noradrenaline neurons in the locus coeruleus, a tiny little hub near the brainstem, deep inside the skull, which has evolved a dense mass of fibers connected to the prefrontal cortex.
The serotonin transporter gene SLC6A4 has been found to correlate with artistic behaviors as well as spirituality, both of which appear to favor the mind-wandering mode. Thus a connection among genetics, neurotransmitters, and artistic/spiritual thinking appears to exist. (Dopamine is no more important than glutamate and GABA and any number of other chemicals.
The warning system is governed by noradrenaline in the frontal and parietal lobes.
Evolutionarily, it makes sense for us to remember unique or distinctive events because they represent a potential change in the world around us or a change in our understanding of it—we need to register these in order to maximize our chances for success in a changing environment.
The second principle of memory concerns emotions. If something made us incredibly frightened, elated, sad, or angry—four of the primary human emotions—we’re more likely to remember it. This is because the brain creates neurochemical tags, or markers, that accompany the experience and cause it to become labeled as important.
The cognitive psychologist Roger Shepard, who was my teacher and mentor (and who drew the monster illusion in Chapter 1), pushed this further in his theory that adaptive behavior depends on an organism being able to make three appearance-reality distinctions.
First, some objects, though different in presentation, are inherently identical.
Second, objects that are similar in presentation are inherently different. For example, in a scene of horses grazing in a meadow, each horse may look highly similar to others, even identical in terms of its retinal image, but evolutionarily adaptive behavior requires that we understand each one is an individual.
Third, objects although different in presentation may be of the same natural kind.
Adaptive behavior, therefore, according to Shepard, depends on cognitive economy, treating objects as equivalent when indeed they are. To categorize an object means to consider it equivalent to other things in that category, and different—along some salient dimension—from things that are not.
We all have an intuitive sense of what constitutes a category member and how well it fits the category, even from a young age.
The point is that when we use preexisting categories, or create new ones, there are often clear exemplars of objects that obviously belong to or are central to the category, and other cases that don’t fit as well.
First, we categorize them based on either gross or fine appearance
A second way we categorize is based on functional equivalence when objects lack similarity of appearance.
A third way we categorize is in conceptual categories that address particular situations. Sometimes these are done on the fly, leading to ad hoc categories.
Each of these three categorization methods informs how we organize our homes and work spaces, how we allocate shelf and drawer space, and how we can sort things to make them easy and quick to find. Each time we learn or create a new category, there is neural activity in a circuit that invokes a prefrontal cortex–thalamic loop, alongside the caudate nucleus. It contains low-resolution maps of perceptual space (linking to the hippocampus); it associates a categorization space with a perceptual stimulus. Dopamine release strengthens synapses when you correctly categorize items according to a
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The scanning technology allows us to pinpoint, usually within one cubic millimeter, where particular neural activity is taking place. This research has shown that the categories we form are real, biological entities, with specific locations in the brain. That is, specific and replicable regions of the brain become active both when we recall previously made categories and when we make them up on the spot. This is true whether the categories are based on physical similarities (e.g., “edible leaves”) or only conceptual ones (“things I could use as a hammer”
Hard boundaries apply mostly to formal categories typically found in mathematics and law. Fuzzy boundaries can occur in both natural and human-made categories.
Wittgenstein concluded that something is a game when it has a family resemblance to other games.
Women’s cortisol levels (the stress hormone) spike when confronted with such clutter (men’s, not so much). Elevated cortisol levels can lead to chronic cognitive impairment, fatigue, and suppression of the body’s immune system
The task of organizational systems is to provide maximum information with the least cognitive effort.
We evolved a specialized brain structure called the hippocampus just for remembering the spatial location of things. This was tremendously important throughout our evolutionary history for keeping track of where food and water could be found, not to mention the location of various dangers. The hippocampus is such an important center for place memory that it’s found even in rats and mice. A squirrel burying nuts? It’s his hippocampus that helps him retrieve nuts several months later from hundreds of different locations.
More recently, we’ve discovered that there are dedicated cells in the hippocampus (called dentate granule cells) to encode memories for specific places.
The phenomenon of place memory was known already to the ancient Greeks. The famous mnemonic system they devised, the method of loci, relies on our being able to take concepts we want to remember and attach them to our vivid memories of well-known spaces, such as the rooms in our home.
One of the big rules in not losing things is the rule of the designated place.
The principle underlying all these is off-loading the information from your brain and into the environment; use the environment itself to remind you of what needs to be done.
The key to creating useful categories in our homes is to limit the number of types of things they contain to one or at most four types of things (respecting the capacity limitations of working memory).
A germane finding in cognitive psychology for gaining that control is to make visible the things you need regularly, and hide things that you don’t. This principle was originally formulated for the design of objects like television remote controls.
Organization Rule 1: A mislabeled item or location is worse than an unlabeled item.
Organization Rule 2: If there is an existing standard, use it.
Organization Rule 3: Don’t keep what you can’t use.
One way to exploit the hippocampus’s natural style of memory storage is to create different work spaces for the different kinds of work we do.
The neurologist and writer Oliver Sacks goes one further: If you’re working on two completely separate projects, dedicate one desk or table or section of the house for each.
Microsoft engineer Malcolm Slaney (formerly of Yahoo!, IBM, and Apple) advocates scanning everything into PDFs and keeping them on your computer.
Earl Miller, a neuroscientist at MIT and one of the world experts on divided attention, says that our brains are “not wired to multi-task well. … When people think they’re multi-tasking, they’re actually just switching from one task to another very rapidly.
Many people under twenty now see Facebook as a medium for the older generation. For them, texting has become the primary mode of communication. It offers privacy that you don’t get with phone calls, and immediacy you don’t get with e-mail. Crisis hotlines have begun accepting calls from at-risk youth via texting and it allows them two big advantages: They can deal with more than one person at a time, and they can pass the conversation on to an expert, if needed, without interrupting the conversation.
You receive a text, and that activates your novelty centers. You respond and feel rewarded for having completed a task (even though that task was entirely unknown to you fifteen seconds earlier). Each of those delivers a shot of dopamine as your limbic system cries out “More! More! Give me more!”
In the case of the DARPA balloons, it required only 4,665 people and fewer than nine hours.
