Week 1, Lecture 1: Default Mode Network

Q1: What is the default mode network (DMN), and how was it discovered?

1990s, These studies covered a range of cognitive and perceptual tasks—visual search, spatial

attention, language, memory, and visual imagery—so the tasks were quite different from one

another.

s anything more active across all of

these tasks compared to the baseline periods when people were just lying there doing nothing

map of four regions: the medial prefrontal cortex (mPFC, toward the front of the brain along the

midline, just behind the eyes), the posterior cingulate cortex/precuneus (PCC, toward the back

of the brain along the midline), the temporal poles (the very tip of the temporal lobe, in front of

the ear), and the temporoparietal junction (TPJ, just above and behind the ear, on both sides of

the brain).

what turns the DMN on is mentalizing.

Mentalizing is the process of making sense of another person's (or one's own) mental states

and psychological characteristics—their beliefs, desires, intentions, feelings, and traits.

Q3: What is the significance of the DMN turning on within 400 milliseconds?

overlap between the DMN and mentalizing was clear,

2 studies,

400ms, ECog,

That is far too fast

for a person to consciously decide to think about something social. Any time there is a break in

the action of even 400 milliseconds, the network grabs those processing cycles for whatever it is

it does. It behaves more like a reflex than a deliberate choice.

we may be so interested in the social world in the first place because this network for

social thinking so reliably and automatically turns on during every break in the action, orienting

us toward the social aspects of the world whether we intend it or not.

Q4: What is the intentional stance, and what does it have to do with the DMN?

intentional stance is a concept from the philosopher Daniel Dennett,——argued that humans have a built-in bias to see certain

physical organizations of matter—in particular, other people—as though they have thoughts,

feelings, and goals;it just shows that we are built to act as if they do.

On this view, evolution has made a bet that one of the best things the

brain can do with any spare moment is prepare to see the world socially.

Q5: How did the rest and mentalizing study work, and what did it find?

This study was designed to test whether DMN activity during rest actually primes the brain for

social cognition—that is, whether it makes you faster at mentalizing if mentalizing is the next

thing you have to do

ppl see picutres with and without a mentalzing statement caption

The analysis focused not on brain activity during the trials themselves but on activity during the

short rest period right before each trial.

• There were three trial types: "why" statements (about the person's goal or

  motivation—requiring mentalizing), "how" statements (about the physical mechanics of the

  person's body movements—not requiring mentalizing), and math trials, included as something

  not remotely social. Each trial was preceded by a brief period of rest.

Treating each trial as a data point, dmPFC activity during rest

predicted performance only when the next trial was a "why" trial: the more dmPFC activity

during the preceding rest, the faster people answered the mentalizing question. For upcoming

"how" trials and math trials, rest activity did not predict performance

• Together, these studies suggest that DMN activity during rest primes a social lens—a way of

  making sense of the world in terms of minds, rather than bodily mechanics, math, or facts about

  the non-social world.

Q6: How do we actually know the DMN is preparing us to think socially, rather

than doing something else?

that DMN activity at rest helps us build social

expertise.
* its lower actviation, during smeantic trials, showed better results on social tasks after DMN activaton

do humans have the biggest brains?

NO, sperm wahles have larger volume.

what is encephalization?

the ratio of brain to body, or more

precisely, the amount of brain tissue we have beyond what is needed to run a body of our size.

What is Dunbar's number, and what does it mean?

Robin Dunbar, Dunbar's number refers to the idea that humans tend to live and work in stable social groups of

about 150 people.

• , he estimated three things for each:

  how innovative or intelligent the species is (a rough measure of IQ), how good its members are

  at imitating each other, and the typical size of the groups it lives in

• The more

  encephalized a species' brain, the larger the groups it lives in.

Q9: Why would social group size be the main driver of brain evolution?

Hunting deer alone is very hard. With a group, some of youcan scare the deer in one direction

• e cost is that other people take your stuff.

• solution is coalitions within the group. If you are part of a coalition, other people are less

  likely to mess with you, because they know they are not dealing with just you but with your

  whole group.

• Keeping track of these coalitions—who is with whom, who can be trusted—is what

  makes group living tricky, and it is a big part of why larger groups demand more brain.

Q10: What was wrong with the traditional view of human nature as "rational self-

interest"?

Put these together and you get

rational self-interest—homo economicus, a creature that is always calculating what will serve its

interests and what will hurt them.

The brain does not use its free time to practice

math or logic. Whenever it has free time, it reliably turns on a network that seems to help us get

better at being social—and even when people do not know they are about to have to mentalize,

more DMN activity at rest primes them to be socially successful right afterward.

Q11: How does mentalizing relate to empathy and theory of mind, and is the DMN

active in newborns?

eory of mind is a

capacity—something you haveMentalizing is something you do: it is the act of applying theory

of mind.

, DMN regions show coordinated activity essentially from the day we are born. You

cannot run a task-versus-rest study with a one-day-old baby, but you can measure whether

these regions are coordinated with one another, and in full-term newborns they are.

• It is as if the network is designed to switch on right when we are supposed to enter the world and start receiving social input.