Why do our minds wander? What the brain's default mode tells us about our humanity

We speak with cognitive scientist Vinod Menon about the brain networks behind day dreaming, rumination, and our sense of self
Nicholas Weiler
From Our Neurons to Yours Wu Tsai Neuro Podcast

Here’s a question for you that may at first seem trivial, but is actually profound: Why do our minds drift? 

If you have ever dabbled in mindfulness or meditation, you know this mind wandering has an almost gravitational pull. In fact, researchers now think we spend as much as 50 percent of our waking time in this state, which cognitive scientists have dubbed the brain’s “default mode.”

Today’s guest is Vinod Menon. He’s a giant in the field of cognitive science who played a central role in defining the brain “default mode network” back in 2003. 

He argues our tendency to daydream may be at the core of our self-identities, our creativity – and also many of our most troubling psychiatric disorders, from Alzheimer’s to ADHD.
 

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Vinod Menon
Vinod Menon is Rachel L. and Walter F. Nichols, MD., Professor of Psychiatry & Behavioral Science at Stanford Medicine, and an affiliate of the Wu Tsai Neurosciences Institute.

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References

Glossary

  • Default Mode Network (DMN) The Default Mode Network is a collection of brain areas that becomes active when we turn our attention inward, away from the outside world. It acts as the brain’s “default setting,” generating our internal mental life—our memories, daydreams, and the ongoing narrative of who we are.

  • Narrative Self The narrative self is the ongoing internal story that creates our consistent sense of identity. The DMN is thought to build this narrative by integrating our memories, language, and emotional experiences into a coherent story that gives meaning to our lives.

  • Posterior Cingulate Cortex (PCC) The Posterior Cingulate Cortex is a major DMN brain region that acts as a central “switchboard” and integration hub. It broadcasts information across the network and is fundamental to self-awareness; damage to this area is linked to profound changes in consciousness.

  • Medial Prefrontal Cortex (mPFC) The Medial Prefrontal Cortex is a DMN node that functions as an “evaluator and emotion integrator.” It contributes to self-reflection and helps us make value judgments, answering the internal question, "Is this important to me?"

  • Angular Gyrus The Angular Gyrus is a DMN region that serves as a “meaning-maker” at the intersection of language and memory. It helps integrate general knowledge about the world with our personal memories and experiences, creating a richer subjective reality.

  • Medial Temporal Lobe (MTL) The Medial Temporal Lobe, which includes the hippocampus, acts as the DMN’s “memory gateway.” It is critical for forming new memories and constantly feeds the network with material from the past, providing the raw data for our internal narrative.

  • Hyperconnectivity Hyperconnectivity is a state of abnormally strong and rigid communication between brain regions. In disorders like depression, DMN hyperconnectivity is linked to rumination, where the brain becomes “stuck” in a negative internal narrative that is difficult to turn off.

  • Transdiagnostic Transdiagnostic refers to a biological or psychological factor that is present across multiple, traditionally separate medical diagnoses. Dysfunction in the DMN is considered a transdiagnostic feature, as it is a common thread linking conditions like ADHD, depression, anxiety, and schizophrenia.

Episode credits

This episode was produced by Michael Osborne at 14th Street Studios, with sound design by Mark Bell . Social media strategy is by Julia Diaz, and additional editing by Nathan Collins. Our logo is by Aimee Garza. The show is hosted by Nicholas Weiler at Stanford's Wu Tsai Neurosciences Institute and supported in part by the Knight Initiative for Brain Resilience. 

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Transcript

Nicholas Weiler (00:10):

Welcome back to From Our Neurons to Yours, from the Wu Tsai Neurosciences Institute at Stanford University, bringing you to the frontiers of brain science.

(00:25):

Here's a question for you that might at first seem trivial, but is actually kind of profound. Why do our minds drift? If you've ever done meditation or mindfulness, you know that this is something that's almost unstoppable. Our minds always drift from one thought to another. It turns out this tendency to daydream might be at the core of what it means to be human. This is what today's show is all about. And to introduce this, I want to take us back for a moment to a surprising observation neuroscientists made back in the 80s and 90s. This was the advent of human brain imaging when PET scanners and later FMRI were letting researchers study the human brain in action for the first time.

(01:08):

Labs around the world were having people come in, sit in these scanners and do specific focus tasks, things like remembering a set of images or reading stories and filling in missing words. These experiments were designed to map the brain at work, charting the regions responsible for perception, language, decision making, and so on. But a few labs started noticing something interesting that was happening in between these focus tasks when research subjects were just hanging out in the scanner waiting for the next thing to start.

(01:40):

These researchers noticed a specific consistent pattern of brain activity always seemed to arise during these offline moments. And whatever this pattern was, it disappeared as soon as participants started the next task. This pattern was so consistent, so persistent that scientists started calling it the brain's default mode. Essentially, researchers had stumbled upon a set of brain networks that are responsible for this thing that is so fundamental to what we do as human beings.

(02:10):

Our minds wander. When we get distracted, when we're not focused on what we're doing, our minds drift away from the here and now, our attention turns inward, and we travel through time and space into the past and the future. We think about the party we're planning for the weekend. We think about the groceries we need to pick up or a difficult email we need to respond to, or we simply daydream and imagine what might be.

(02:36):

Researchers now think we spend as much as 50% of our waking time in this state. Today's guest is Vinod Menon. He played a central role in defining the default mode network in the brain back in 2003, and he's a giant in the field of cognitive science. He told me he hasn't done too many podcasts before, so I was thrilled to have him join us from our neurons to yours.

(02:58):

We talked about how this default mode network may be at the core of everything from our self identities to our creativity and also many of our most troubling psychiatric disorders, from Alzheimer's to ADHD. I started our conversation by asking Vinod to give us his definition of the Default Mode Network.

Vinod Menon (03:17):

So the default mode network is a collection of brain areas that becomes active when we turn our attention inward. And it's a network that generates your internal mental life, your memories, your sense of who you are, your plans and daydreams, and the ongoing inner narrative that reflects our own individual experiences. This is not a passive network. It's increasingly now recognized on a key intrinsic functional brain network essential for high level human cognition. One of the key aspects of this system is that it's actually suppressed during externally focused tension demanding tasks. And so this is a system that is switching on by default. It's the brain's default setting.

Nicholas Weiler (04:12):

So you've been looking at this as a network of brain regions. I want to sort of start by trying to paint the picture for people of the experience that we're talking about. What is the thing that people will recognize from their daily lives and why we think we spend so much time there. And then I definitely want to dive in with you to what are some of the pieces of this? How have we defined this as a mechanistic brain network that becomes active basically anytime it can, anytime that we're not focused on something else? So what are some of the experiences that listeners may have where after listening to this conversation, they might say, "Okay, that's my default mode network. I'm in default mode space"?

Vinod Menon (04:57):

Right. So the experience of DMN engagement is actually deeply familiar to all of us. And it's a sense of being in your head. So what does this feel like? The moment when you're driving a familiar route and suddenly realize that you've gone several miles without really noticing, your attention has drifted inward. You're still functioning, but you're not focused on the road. You're replaying a conversation from earlier or thinking about what you might need to say to someone later, or you're walking in the park not thinking of anything in particular, and suddenly you have an insight about a problem that's been bothering you. That's your DMN making connections between ideas, memory, and semantic knowledge that you've built up over the years. Or you catch yourself daydreaming during a meeting, constructing a whole scenario about your weekend plans or reimagining a past conversation that could have gone differently.

(05:52):

Or you're reading a book and a few minutes later you realize that your mind has been wandering and you've not been paying attention to the letters on the page.

Nicholas Weiler (06:00):

And I want to come back to this idea of it being our default mode. I mean, this was originally identified based on some sort of odd observations back in the 1990s where folks who were using PET brain imaging noticed that anytime someone in the study was not actively engaged, their brain would default to this other mode. And so why do you think our brain defaults to this mode? What is going on that makes this our brain's preferred state, essentially?

Vinod Menon (06:32):

Yeah. For one, it's a highly metabolically active system, which is required to kind of keep the system going.

Nicholas Weiler (06:41):

You mean it's taking more energy than you might expect?

Vinod Menon (06:44):

Yes.

Nicholas Weiler (06:44):

It's not restful necessarily.

Vinod Menon (06:46):

Yeah, because it's constantly active and that is energy demanding process. And so why might this have come about? And I think it's partly because of the complexities of the human brain. As the system has become more complex, it's evolved systems to regulate itself, to be not just reactive, but to be reflective. Taking the demands, the multiple cognitive demands that can be put on the system and to take that and give it more meaning and to be separated in time from those specific events and to have a sense of keeping a distance both in space and time and through the ability to kind of plan and reflect to bring new ideas that are independent of the stimulus that they've been exposed to in the past. So to create meaning, to create an inner narrative that is built on many different components of this system.

Nicholas Weiler (07:46):

Well, you had a really nice review article sort of reflecting on the past two decades of thinking about this default mode and the default mode network in the brain that you published a couple of years ago. And you wrote that you viewed this network as sort of integrating language and memory to create an ongoing internal narrative, basically our sense of having a consistent self, which is a very heady idea. So help me understand that. How does my mind wandering when I'm supposed to be doing something else contribute to me having a internally consistent sense of self?

Vinod Menon (08:24):

So if you look at the functional components of the system, the anatomical functional components, that gives us a clue in terms of what the system might be doing. And it sits at the interface of a number of different systems in the brain that's spread out across the semantic, language, memory, evaluation and emotional integration, and core hubs that integrate signals from very broad areas of the brain. So it's sitting at the nexus of all these processes, and then one can ask from an evolutionary point of view, what are the novel features of the system that exist in the human brain for which there are no known homologes in not only human brains, but also non-human primates?

Nicholas Weiler (09:08):

That's a really interesting question. So you're saying, how can we look at what is uniquely human about this network?

Vinod Menon (09:14):

Yes. And if we look at that, we see two or three essential components. One is the language ability, our ability to communicate narratives and to process sequences of information involves multiple frontal lobe areas. And then there's the semantic system that builds off from all our memory experiences and creates generalized knowledge. And these are systems that have really significantly expanded human brain, and consequence of that is integrated system that allows information to be pulled together and to be thought about and accumulated over time, independent of and quite distinct from the specific experiences that we've had. And so the thinking was, what are the unique features that might then contribute to this reflective sense? Which led me to propose that there is a common theme in all of these disparate literatures that have evolved in relation to autobiographical memory, thinking about the past, thinking about the future, the semantic knowledge that this system subserves.

(10:24):

The common underlying theme is a narrative, a description of what our experiences are so we can consciously reflect of them. Not all the information that's processed in the system is necessarily conscious, but it does underlie a narrative self that helps us reflect and sustain information and think about sequences of narratives and in a much more rigorous way than is possible with much more primitive brains.

Nicholas Weiler (10:54):

Let me see if I'm following you. So you're saying that the fact that we have these sort of linguistic or semantic systems that allow us to take our memory of what we did yesterday or what we did this morning, what we're planning to do in the future, and create a story around it, and that internal storytelling that you suggest that this is what we're sort of doing in this default mode that our brain goes into when we're not actively engaged with the outside world, we are telling a story to ourselves about why they matter to us as opposed to just a record of whatever happened in our experiences.

Vinod Menon (11:36):

Yeah. So one way to think of it is they're not just individual isolated events that are being recalled. They follow an underlying narrative schema and it's that process that's, I think, captured by the collection of these nodes that constitute the default network.

Nicholas Weiler (11:56):

I want to hear more about how this evolved and how unique this is to us as human beings. I mean, where I'd love to go in this conversation as we dive more into this is this idea of the default mode network came about a couple of decades ago. It's been increasingly implicated in not only these big ideas about how we come up with the narrative of who we are, but also in a more holistic understanding of some of the mental health challenges that people face, some of the ways that our internal narrative can go awry in a way that really is detrimental. And I think to get to that, it might be helpful to start talking about some of the specific parts of the brain that are involved in this network and how they talk to one another.

(12:41):

The idea of the default mode came from these PET imaging studies from the 1990s and led your colleague, Marcus Rako at Washington University in St. Louis to come up with this idea of a default mode. Whenever the brain's not doing something else, it defaults to this mode. But then you and your team came in and really defined what is the network? What is the brain network that is engaged during those times of internal reflection when the spotlight goes from the outside world to the inside world? I don't want to get into too much detail, but can you tell us a little bit about this network that you defined? What are the components of the brain and how do they contribute to this reflective state we all spend so much time in?

Vinod Menon (13:44):

Right. Let me give you a little bit of a tour of some of the areas involved. But first, I want to say that when Mark first proposed this idea for default mode, which actually goes back this prior work as well, but he was the one who actually

Nicholas Weiler (13:59):

I think William James was writing about something along these lines before neuroscience really existed.

Vinod Menon (14:04):

Exactly, exactly. And so this kind of stream of consciousness framing that's so prominent in his work, very innovative ideas, but till these studies came along with human brain imaging, we had no idea about how these systems might function, where they're represented in the brain and so on. And so some of the key anatomical components of this were already identified before and the work actually stagnated for a couple of years, and Mark tells us that this work was not taken seriously. And so it's really when we came and published the study in PNAS showing that with FMRI, that these areas form a couple network, they are cohesive in space and time and it really propelled the field into new directions by saying, "Well, these are not just isolated systems. They actually are a coherent unit."

Nicholas Weiler (14:59):

So was it sort of that people were saying, "Yeah, we know that when people aren't doing something, they might be remembering something. And so naturally the hippocampus might be active, that on its own wasn't enough until you were able to say, actually all these systems appear to be talking to each other and not just by chance, but there's some active mechanism where whenever it can, the brain switches all these systems on for some active process."

Vinod Menon (15:28):

Right. And now with the FMRI time series data, we could actually show using a working memory task that you get this dynamic process. Intrinsically they're coupled where we start to do a working memory task, these areas are suppressed. So we showed this whole process happening in a much more dynamic way than was possible with PET imaging, which is kind of now what established the notion that this forms a coherent network with certain properties. And the properties are, they are intrinsically coupled and they can be actively suppressed very dynamically on the timescale of seconds as we engage with the external world to do a complex task or being enhanced when we are at a low level task condition or a baseline condition, so called resting state.

(16:15):

And so now to get back to your question about the anatomical components we've known now from our body of work, from our labs and many other labs, the posturcingulate cortex, this is one of the most consistently activated regions as part of the DMN, and it's a core hub, it's most widely connected to the rest of the brain. And so this is in the posterior midline protected from potential injuries on the surface.

Nicholas Weiler (16:43):

In the back of the brain, in the middle. I'll translate the Latin.

Vinod Menon (16:45):

Yes. And we don't think about it in those gross terms, but that's right. So it integrates information from other DMN areas and broadcasted globally. And when it's damaged, people often experience profound changes in self-awareness and consciousness. It underlies disorders of consciousness, minimally conscious states, significantly impacts the posturocingular cortex. And in some sense, when you come out of consciousness, this is one of the key systems that has to come on before you have a sense of being conscious. There's a lot of aspects of conscious processing and tasks and subliminal versus conscious processing, but this is a very natural kind of set of states that the brain can toggle to. And in cases of injury, it really provides us insight that it analyzes this type of states of consciousness where you can report and respond and so on in ways that you could not in a unconscious state.

Nicholas Weiler (17:46):

Okay. So we have the posterior cingulate as a hub that is directing traffic, let's say, and broadcasting information back out to the rest of the system. And if it's injured, you sort of lose this default mode activity as a whole and people experience loss of consciousness or loss of awareness essentially.

Vinod Menon (18:04):

That's right. That's right. And the studies from which that's most clear actually are studies of minimally conscious individuals, as well as we'll get to a little bit later, Alzheimer's disease. And so the X has a switchboard and integration center, and it functions in very close collaboration with medial prefrontal cartex, which is an evaluator and emotion integrator, and its contribution is self-reflection, thinking of your own mental states, emotional appraisal, making value judgments. So for example, when you think, "Is this important to me?" And that's likely a medial prefrontal cortex contribution because it has very strong links to the affective and limbic system. And it helps to regulate emotionally how significant the narrative becomes and it's also impacting depression, as we'll discuss later. The third region is the angular gyrus, which sits in the temporal parietal areas, just about few years, and its contribution is to integrate a semantic knowledge, facts, concepts, and word meanings with personal memories and experiences.

(19:13):

And so it sits at the intersection of language, memory, and meaning making. And it's an essential component, which is another one if we talk about this in an evolutionary sense, there's no homologe of this in the non-human primate and its damage can produce some fascinating resolve deficits. For example, losing the subjective feeling of remembering, even when you can recall a fact. And then there's the medial temporal lobe, which is the memory gateway critical formation of memories, and its contribution is retrieving specific personal memories or contributing to the retrieval, and it's constantly feeding the DMN with material from the past, and that's why you see significant impairments in Alzheimer's disease, which often starts in the medial temporal lobe and profoundly disrupts not only memory, but a sense of self as well.

(20:04):

The last major component of this is the lateral temporal cortex, again, significantly expanded in the human brain, and it plays a key role in processing language and semantic information that helps sustain the language narrative component of it because it has links with the semantic and language systems. So these areas, they've been studied from many different angles in the past 100 years from a lesion point of view, historically in neuropsychological studies, but with PET imaging and then with functional imaging. And these areas are sitting as part of multiplex systems in the brain. And what the DMN does is bring key elements of the processes that are sustained by these systems into coherent whole for this type of information processing that we've been just discussing.

Nicholas Weiler (20:58):

I think that's so interesting. And I wonder how this changed the way that people, at least in your part of the field, have been thinking about some of these areas. Because as you say, people have been studying all of these areas for a century, thinking about their particular roles in memory or in language and so on. And what I'm hearing is that based on this observation that these were getting quiet when someone was focused on a task and then getting active again as soon as someone wasn't focused on a task, and then your work showing that not only are these active, but they're all talking to each other, dynamically coupled, they're all coupled with each other, there's signaling, there's activity going on. Understanding how these parts of the brain, how memory, how language and sort of how these all get connected to each other, that this forms a distinct network, that the brain is actively turning on and off depending on the situation.

(21:57):

Was that a different way of thinking about brain networks and our cognition?

Vinod Menon (22:01):

Yes. I think it wasn't really appreciated. The brain is organized into these fairly spatially segregated systems that serve reasonably distinct functions. And the notion that at least the human brain can be carved up into these networks was just becoming prominent 20, 25 years back. And of course, network models of brain function are all over the place from many different angles, many different theories of how they function and so on. And so this really brought not just an understanding of this particular network, but there are other dedicated systems and it's not the function in isolation, we have to remember this, but they subserve certain unitary functions which are generally very difficult to distinguish. And this allows us to build some theoretical framing. Instead of talking about two to 300 brain areas, we can talk about systems that regulate certain kinds of processes now, and it's also very dynamic in the sense that it can come in and out, and there are connector hubs that might talk across networks and so on, but it creates a general principle for underlying, for studying global brain function.

Nicholas Weiler (23:13):

And the other thing that you mentioned as we were doing this sort of grand tour of the different parts of the brain that are involved in this internally reflective state was several of these areas are pretty distinctly or uniquely human. And so I think this is going to be a good time to start talking about what happens when some of these things go wrong. Does looking at these brain areas give you any sense of how this particular network evolved in human beings and for what purpose? I mean, it seems like it's a lot of the brain, it's a lot of our time. And so it's a little bit surprising in a way if we don't see a homologue of this or an equivalent in other animals, right? Not that much of our brain is different. So to refine my question, does looking at these different brain areas and how they're connected give you a sense of how this network came about in humans and maybe why it's so important for us?

Vinod Menon (24:11):

Yeah. So if you look at some of these systems like the core medial temporal lobe circuit, that's involved in memory replay and spatial navigation in rodents and similar function in monkeys, although less well study. So it suggests that there's some primitive anchoring with the memory system. And then as we discussed, there's been expanded set of areas that's been added to this evolutionarily. And this now allows us to make some educated guesses about how this might have evolved. In one sense, I kind of alluded to this is probably emergent property of increasing complexity in the brain. We've added so many more regions and much more complex cell types, and it's a system for maintaining control, I think, when the brain becomes too complex to operate as a stimulus response or a habit-forming system, which we see in all animals, essentially. But critically in the human brain, this allows us to create systems that are separated from those stimulus response contingencies and purely habit-forming.

Nicholas Weiler (25:19):

It's almost like having a buffer in a sense. I'm thinking about, we had this very interesting conversation about neural networks and human intelligence and AI with your colleague, Jay McClelland earlier, and I'm sort of reflecting back on that, that like in humans, maybe what we have, as you're saying, is going from just, how do I process what I need right now to respond to the environment and to optimize my getting food, reproducing and so on, to having this bigger buffer, this bigger workspace of an ongoing narrative of what are my goals? What are my objectives? Who am I with relationship to these other people? And so by having more bandwidth sort of you're suggesting, you can start applying some of those baseline systems like maybe mice are replaying how they got to some food yesterday, but we are replaying, how did my conversation with so-and-so go and is that going to get me a promotion or is that going... Did they understand what I was saying? How do I interact with them the next time I meet them?

Vinod Menon (26:24):

Yes, exactly. So that allows us to separate ourselves from the contingencies of the stimuli that we've processed and to be reflecting on it and also have those long-term history. I mean, I can think about events from 30, 40 years back in my life if they were salient and reflect on them like all of us. And so while these short-term replays exist in other species, it's hard to conceive of these long-term events in some reportable manner. And then go back to your question about what is actually telling us about disease states. And so once we've identified these regions and the functions they serve and the circuits that they're embedded in, then we can think about, for example, in the case of the posturcingulate and the medial temporal lobe damage, there's not just a memory deficit that exists in Alzheimer's disease, it's eventually also a sense of self, an impoverished narrative. The social interaction with others is also impaired because you don't have the machinery to kind of think about yourself in the context of others. And the DMN, 70% of the time it's been estimated is involved in the social replay.

(27:33):

It's not just memory of what I ate yesterday, but who did I talk to? What was the nature of my interaction, what it should be tomorrow and so on. We have learned a lot by piecing together the elementary functions of these regions to get a sense for what broader cognitive profiles of deficits might arise beyond just saying, well, memory is impaired in Alzheimer's disease, because it's just much more than that as the disease process cascades into multiple systems. And there's actually very interesting research showing that the trajectory of disease progression actually follows network changes. So you're more likely to see changes in DMN nodes before you see changes in other systems, because the seed for disruption actually arose in a node of the DMN. And I think the Alzheimer's disease is a very good example of that.

Nicholas Weiler (28:27):

Yeah, that brings two ideas to my mind. I'll try to keep them both in my mind while I ask you about them. I mean, I think it's one of those things where I feel like you always hear Alzheimer's disease, the first really frank symptom that usually gets someone to diagnosis is memory problems. And sure, that makes sense because the hippocampus, which is involved in memory, is affected. And at one level of thinking about it, okay, that makes sense. Memory is affected, the hippocampus is affected, but it's much more complicated than that. Alzheimer's, as you say, is much more than just a memory problem. And so thinking about this bigger network, well, what is the functional network? How do we use our ability to recall specific memories and how does that get impaired? So as you say, it's not just that I don't remember what happened, it's that I don't remember why it matters.

(29:16):

I don't remember why it matters to me, and I don't remember how it connects me to other people. And so taking that lens of thinking not just about damage to a particular brain region that's connected to some particular function, but how that affects the global network that that particular brain region is involved in.

(29:36):

And that leads me to the second point that you raised, which is the brain is very redundant. Our brains are very big, lots of neurons, and we're really good at resisting damage to the brain. In fact, keeping with the Alzheimer's conversation, the damage to the brain is happening for decades before you or anyone else notices, but the brain is able to adapt and reroute things and figure out a way. But when the damage gets bad enough, it's these larger level networks where you're going to see the failure cascading. As soon as it can't adapt, this network is going to experience a problem.

Vinod Menon (30:14):

I think that's very well put. I think if you have isolated some area, there's probably multiplex that can compensate for it. But when the disruption has reached this very large scale level, that's when the impairments are so significantly manifest that it really feels like the sense of self is gone and this is really a different individual. This is seen to much less extent in various psychiatric disorders as well and there's much more punctate and often does not have an underlying morphological or structural deficit, but there's a functional process that's impaired. So in relation to the disorders and particularly psychiatric disorders, I wanted to mention that I think it's useful to think about the DMN as the hardware that supports a range of functions. Now it can be loaded with lots of different software processes. Our internal mental representations are very unique to us based on our own individual experiences and the lifetime events that we have gone through.

(31:16):

So it's important to separate this notion that the network is dysfunctional from what are the contents of the network that's dysfunctional. And the contents that are dysfunctional range very widely across disorders, as they range widely in difference across to individuals, or maybe even siblings and maybe even someone who've grown up in the same household. So there's this very personal sense of what this system encodes, that things that we value, things that matter to us and our own personal experiences. When we talk about different practices and different disorders, practices, I mean contemplative practices, which we can get to in a bit. It's really not that the system is now engaged, but it's engaged in a very different way based on your experiences and practices.

Nicholas Weiler (32:07):

Yeah. I mean, it seems like this sort of network perspective to this helps us understand both why these disorders are so complex and nuanced and affect many different areas of our lives in ways that you might not expect when you think about one brain region at a time. But also as you say, it's going to be very unique how a particular physical damage to this system is going to impact the software that you've been running.

(32:36):

Well, let's go through some other disorders where there's evidence for a role of the default mode network, just sort of to try on this lens to say, "Okay, what if we think about attention deficit disorder through a default mode lens?" And then let's do a few of those. And then at the end, I'd love to just sort of go back to why does this matter to us, to listeners? Maybe how can we think about our own default mode?

(33:03):

So let's start with a few of these things. I think we've been talking about the spotlight of attention. So attention deficit disorder seems like a natural place to try to apply this way of thinking. How do you apply a default mode network frame to that disorder?

Vinod Menon (33:17):

So in ADHD, children and adults with the disorder show in appropriate DMN activation during tasks that require external attention. So the network is not, keynotes of the network are not suppressed when you need to suppress them, leading to attentional lapses and difficulty staying focused. This is not just ADHD, by the way. I mean, if I were to do a task for a very long period of time and I have a lapse of attention on trial number X, let's say, we're going to see the same process. And so it's just that the occurrence of these processes is much more prominent and frequent in individuals with ADHD.

Nicholas Weiler (33:52):

So the idea is that there's a process that's basically suppressing the default node during a other task. And in ADHD, we see that whatever is keeping the default mode network at bay isn't working properly. And so the spotlight goes internal when we're trying to keep it external. With some people with ADHD, there's also the type of ADHD where people get very hyper focused on something that they're doing that matters to them. Is there a different explanation for why that might be happening?

Vinod Menon (34:25):

I think that's been much less studied. And so then it really becomes also a question about how does it manifest in these individual subtypes and what do their circuits look like?

Nicholas Weiler (34:35):

Right. But in some sense, the switching between focusing on the outside world and focusing on the interior world is not functioning as expected.

Vinod Menon (34:44):

I think that's probably the most parsimonious explanation. And so that brings in other networks into play, which are how external stimuli gets regulated and then its impact on the DMN. But there's some very interesting work that I think will happen in this context of heterogeneity, but we don't know enough yet at this point.

Nicholas Weiler (35:04):

And I think it's important to reflect just as we're talking about these various conditions, that some of this is also just natural variation, right? And we call it a disorder if it's disrupting someone needs to be in school and paying attention to their teacher or what have you, being in your head. And so as you mentioned, this is very important for creativity and making connections and making that narrative of the self. So we have a variety of kinds of brains and some of them are better suited to school and the modern workplace than others.

Vinod Menon (35:38):

Yeah. And even within our own kind of day-to-day experiences, focusing on external stimuli and processing them appropriately with the right cognitive processes being brought to bear, whether attentional or working memory or semantic links, but then also to have a different system that's able to separate itself and think about the largest scope of these things, devoid of the specifics of the individual stimuli.

(36:31):

To get back to the question of psychiatric disorders, I mean, the deficits are major in pretty much every psychiatric disorder that's been studied, and it seems like there's a transtagnostic component to it that's seen mostly in structural imaging studies. So it's impacted, we know that. And the functional imaging studies with cognitive tasks are telling us what is the nature of the representations and task information processing that's actually disrupted and the reasons vary across disorders.

Nicholas Weiler (36:59):

Yeah, but that's an important point that one of the advantages of looking at this network level is that it helps us understand this theme that emerges in a lot of our conversations about these disorders being more related than we traditionally think of them as being in medicine where it's like everything has to fit in its own bucket.

Vinod Menon (37:18):

Right. And psychiatry, that's prominent. Comorbidities are prominent across any pairs or multiple sets of disorders. Autism and ADHD has a lot of overlap, maybe even a third of individuals who have autism have ADHD, maybe more. And so there are different research strategies for studying each of these and for understanding how the system gets parsilated into these subtypes, and that's still very much ongoing work. We have a broad sense of dysfunction in these systems, but in some sense, it's too broad to pinpoint exactly what the nature of those, as I mentioned, not just circuits, but the representations are, but they manifest themselves in very different ways. But I think the framing of these systems as part of a network allows us to think of about them in some coherent way and very disjunctively, which is really important, certainly from a transdiagnostic point of view.

Nicholas Weiler (38:14):

Yeah. So let's think about another sort of class of traditional diagnoses and how we can think of that from this default mode perspective. Let's talk about anxiety and depression, which are distinct, but sometimes grouped together.

Vinod Menon (38:28):

Yeah. Right. So in depression overactivity in keynotes of the DMN, particularly the medial peripheral cortex, the one that deals with emotion and value evaluation, and it's what we call hyper connectivity. So system is story wide that it's unable to, and it's very difficult to switch off the system, but more than that, it's also the contents which are very negative affect driven and get, the system gets stuck in a negative internal narrative rumination. And so it's a very interesting example to show that it's not just a circuit deficit, but it's actually what the content is. So you could have other disorders with this kind of profile of hyperconnectivity, but don't really manifest themselves as depression. So the contents that the individual engages in based on their experiences and so on, really becomes quite central to understanding the range of dysfunctions that is altered by the DMN.

(39:31):

And anxiety of excessive DMN connectivity with emotion and threat related regions and this notion we discussed about planning and assimilating the future has now become very threat focused and the ability to imagine the future normally adaptive for planning goes into overdrive and every possible catastrophic event is not stimulated and prepared for in ways that are maladaptive.

Nicholas Weiler (39:57):

I'm really interested by what you said about, you could see similar sort of network level dysfunctions like hyperconnectivity being really stuck in this internal reflective mode, but the contents might be what determines whether that expresses itself in an individual as being fixated on sort of negative self-thoughts or on threats in the future or other things. Are there other sort of diagnoses where you might say it might look similar from a brain imaging perspective in the default mode network, but depending on the contents, you're going to see a different expression. Are there other examples of that beyond depression and anxiety?

Vinod Menon (40:37):

Yeah. I mean, so you have another kind of canonic example is PTSD. Here, now the DMN's narrative structure I think is hijacked by traumatic memories. Again, we discussed then as a strong link with the hippocampus as a keynote of the system, which causes intrusive thoughts from the traumatic events, then we see globally manifest as altered sense of self because the traumatic memories have in some sense taken over what the individual thinks is central to their lives. That's another example. There's also work showing in schizophrenia dysfunction, fragmented networks from another side. Some systems are hyper and some are hypo, even within DMN nodes. And so the ability to distinguish between internal and external reality gets blurred, and this then causes a cascade of impairments, including hallucinatory events now that are given significance in ways and narratives in ways that are very maladaptive. So we all might have events where we say, "Well, this is really nothing that I've actually experienced." It's an odd signal and I don't pay attention to it now.

(41:45):

On the other hand, if you have a hallucinatory event where you take this in, an internal event and braille the narrative around it, then that then leads to all kinds of maladaptive behaviors, including [inaudible 00:41:56] disorders because it's now taken over that narrative. So from a narrative point of view, I think the schizophrenia and thought disorder, also a very prime example of what can happen in relation to DMN dysfunction.

Nicholas Weiler (42:10):

Yeah, that's so interesting. We had a very interesting conversation with your colleague Jake Ballen about schizophrenia and the idea of sort of building that narrative. And if part of the default mode network we're talking about is linking experiences to what matters to you and what is part of your narrative, if that part of the system is putting irrelevant things into the narrative of what matters to you and what's important, then you could imagine building this narrative that's disconnected from what Jake called consensus reality.

(42:39):

Okay. So there's so much more we could talk about and I'd love to have you back on as this work progresses to hear about the frontiers of how we're thinking about the networks behind these various disorders. In the last few minutes that we have, I'd love to take a step back and say, what can we learn from all this, from taking this perspective if listeners are coming to this and coming away with a new perspective on their own default mode, this mode that their brain wants to be in a lot of the time if they're not doing anything else. How can we build a better understanding of ourselves by thinking about the default mode in that way?

Vinod Menon (43:17):

So I think maybe this might be one of the most important takeaways is there is a system for reflection, creating an internal narrative and a sense of the self. In the modern world, of course, we are embodied with all kinds of stimuli notifications, social media that grab our attention, and this is keeping us away from some of the reflective thinking that we could perhaps engage in.

Nicholas Weiler (43:42):

It seems like we go through a lot of trouble and expense to avoid spending time with our default mode network these days.

Vinod Menon (43:47):

Yes. And so whether that's good or bad is for individuals to make their own kind of judgments. But I think some of the key features are it's important for your own sense of identity, it's important for mental health, dysfunctional regulation, inability to regulate these systems, not just a DMN, but it's interaction with other systems, as we've just discussed, underlies a number of psychiatric disorders. And this internal mental life is real work. There's a system, it's a highly metabolic active system, it defaults to it, and it's an almost like evolution has given this to you for free and you can tap into it, you can engage with it, you can alter its contents through a number of different ways, including meditative contemplated practice. It could be as simple as going on for a walk or engaging in a social interaction, which then builds a richer set of representations.

(44:46):

And this notion, I think, that daydreaming and mind wandering are not good for you. I think we've focused a lot on achieving things by paying a lot of attention to the external world, but here you have a system that allows us to think about things without distraction, to also create new associations that we might not have thought about when we are confronted with bombarded with external stimuli that we are on a day-to-day basis and allowing the mind to wonder in this way, in a sustained way, and to change its contents however you decide to do in one's own personal life and sense that makes mean to you could be an advantage in terms of mental health, in terms of a coherent sense of self and interaction with others.

(45:38):

And because for social interaction, this is a system that is going to be engaged. It's going to simulate how we interact with the world. And so much as we can simulate what we will eat for breakfast tomorrow, we can simulate how we will interact with others. And so if those things matter to one, then I think here's the machinery that one could tap it to.

Nicholas Weiler (46:03):

Well, I think that's a beautiful place to end. I mean, many, as I said, we have so many kinds of stimulation. We have our phones, we have streaming on Netflix, we have all these ways to distract ourselves that don't give us that opportunity to reflect and build on our internal narrative and make those creative leaps. My kids always say, as soon as they're not doing anything, they start complaining that they're bored. And let's bring boredom back. Sometimes that's really good for making those connections and connecting with who we are. Well, thank you so much, Vinod, for coming on the show. This has been really fascinating. And as I said, I'd love to have you back to delve into some more of these topics.

Vinod Menon (46:42):

I'd be delighted to. Thank you so much, Nick, for having me. It's been a pleasure.

Nicholas Weiler (46:47):

Thanks again so much to our guest, Vinod Menen. He's a professor of psychiatry, neurobiology, and education at Stanford University and a member of the Wu Tsai Neurosciences Institute. To read more about his work, check out the links in the show notes. And as always, if you're enjoying the show, please subscribe and share with your friends. It may seem like a small thing, but it really helps us grow as a show and bring more listeners to the frontiers of neuroscience.

(47:14):

We would also love to hear from you. If you are listening to the show, we want to know what you think. What do you love? What do you hate? What could we do differently? Send us an email at neuronspodcast@stanford.edu, or leave us a comment on your favorite podcast platform. Before we get to the credits, here's a little preview of what you can expect next time on From Our Neurons to Yours.

Speaker 3 (47:37):

We know a lot about how the mother's body changes, and of course, we know a lot about how the baby develops in the womb, but we know very little about how it is that the mother's brain adapts to the requirements of pregnancy to support both the mother and the baby.

Nicholas Weiler (47:55):

From Our Neurons to Yours is produced by Michael Osborne at 14th Street Studios, with sound design by Mark Bell. I'm Nicholas Weiler. Until next time.

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