Toward a Science of Consciousness, Day 2: Mind Wandering, Default Networks, and Consciousness

OK, first thing to know is that "mind-wandering" is what we used to call, being unscientific and all, spacing out or day-dreaming. Now it's this big important field of study for the consciousness folks - there is a Plenary Session on it (that I can't attend, unfortunately) and a concurrent session on it, as well as various references in nearly every session I have been in so far.

There is some very cool insights into the neuroscience of meditation coming out of this work, so if you are interested, please read through the early material to get to the good stuff at the end.

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Here is a little more information on mind-wandering, via Wikipedia:

Mind-wandering is important in understanding how the brain produces what William James called the train of thought and the stream of consciousness. This aspect of mindwandering research is focused on understanding how the brain generates the spontaneous and relatively unconstrained thoughts that are experienced when the mind wanders.^[7] One candidate neural mechanism for generating this aspect of experience is a network of regions in the frontal and parietal cortex known as the default network. This network of regions is highly active even when subjects are resting with their eyes closed^[8] suggesting a role in generating spontaneous internal thoughts.^[7][9]

In addition to neural models, computational models of consciousness based on Bernard Baars' Global Workspace theory^[10][11] suggest that mind-wandering, or "spontaneous thought" may involve competition between internally and externally generated activities attempting to gain access to a limited capacity central network.^[12]

So, then, what part of the brain is responsible to mind-wandering? Why, the default network, apparently.

The default network is a network of brain regions that are active when the individual is not focused on the outside world and the brain is at wakeful rest. Also called the default mode network (DMN), default state network, or task-negative network (TNN), it is characterized by coherent neuronal oscillations at a rate lower than 0.1 Hz (one every ten seconds). During goal-oriented activity, the DMN is deactivated and another network, the task-positive network (TPN) is activated. It is thought that the default network corresponds to task-independent introspection, or self-referential thought, while the TPN corresponds to action, and that perhaps the TNN and TPN should be considered elements of a single default network with anticorrelated components.^[2]

You might be wondering why anyone cares what the brain is doing when it's doing nothing. The answer is that "nothing" is most of what the brain does.

I want to summarize a few of the presentations from last night and today - all of which relate to this topic in different ways. I will try to go in the best order for making sense of this material, not in the order in which I experienced the material.

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This morning's first Plenary Session was supposed to feature Marcus E Raichle talking about "Brain Dark Energy and Default Mode Networks," but Raichle could not make the conference, so his work was summarized by Stuart Hameroff.

You also can read a good summary of his research in "The human brain is intrinsically organized into dynamic, anticorrelated functional networks," available free online through PNAS.

In essence, most of the brain research looks at the brain while it is performing a specific activity, and any other activity in the brain was considered "noise." Over time, researchers have come to see the default mode network (DMN) as responsible for internal-oriented brain activity, such as mind-wandering, meditation, day dreaming, creativity, self-referential thought, future-oriented thought, episodic memory, and a whole mess of other things. On the other hand, the thalamo-cortical network (TCN) is responsible for outward-oriented brain activity such as problem solving, communication, sensory-motor activity, and so on.

Intrinsic correlations between a seed region in the PCC and all other voxels in the brain for a single subject during resting fixation. The spatial distribution of correlation coefficients shows both correlations (positive values) and anticorrelations (negative values), thresholded at R = 0.3. The time course for a single run is shown for the seed region (PCC, yellow), a region positively correlated with this seed region in the MPF (orange), and a region negatively correlated with the seed region in the IPS (blue).

What also has been discovered is that these two networks, in the absence of a specific task, seem to oscillate back and forth every 10 seconds or so (referred to as anti-correlation).

One theory, presented in a session last night by Kevin Brown (A Systems Model for Selectivity Between Default and Task Modes), suggests that the locus coeruleus may act as a "gate-keeper" between these two systems. Here is the abstract of his presentation:

A Systems Model for Selectivity Between Default and Task Modes. Kevin Brown, Jonathan Smallwood; Jonathan W. Schooler; Jean M. Carlson (Physics, University of California Santa Barbara, Santa Barbara, CA)

Neuroimaging data suggests that the human brain has at least two attentional states - a task-focused mode in which attention is focused externally on the task at hand and a less constrained internal mode dubbed the default state. An essential step to understanding the distinct processes governed by these different states is to understand the way in which the brain divides finite cognitive resources and selects among externally- and internally-driven goal states. We present a coarse-grained, systems-level dynamical model which explores the temporal nature of the interaction between these different modes, in which we examine the role of the locus coeruleus in modulating between external events and internally generated signals. We discuss the implications of the model for understanding mindwandering and attentional failures, which we characterize as partitioning of cognitive effort away from externally driven tasks to internally-generated ones. We also discuss the potential of directly fitting the dynamical model to multimodal dynamical measurements (surface EEG, BOLD fMRI and pupillometry data).

I would like to see the whole article. It's unclear in the abstract and from the presentation what kind of proof there might be for this. However, it's an interesting idea.

In his summary of Raichle's work, Hameroff speculated (against his own ORCH OR theory, which he kindly set aside to talk about this material) that consciousness may reside in the oscillation between the DMN and TCN. Moreover, the DMN is self-organized and may be associated with the narrative flow of self (as mentioned above in the Wiki entry on mind-wandering).

And here is where it gets interesting to me.

The DMN is activated in transcendental meditation (TM), while the TCN is activated in focused attention (single-point awareness on an object, image, or mantra).

A new EEG study conducted on college students at American University found they could more highly activate the default mode network, a suggested natural "ground state" of the brain, during their practice of the Transcendental Meditation technique. This three-month randomized control study is published in a special issue of Cognitive Processing dedicated to the Neuroscience of Meditation and Consciousness, Volume 11, Number 1, February, 2010.

Specifically, the study found the TM technique:

• Produces a unique state of "restful alertness," as seen in the markedly higher alpha power in the frontal cortex and lower beta and gamma waves in the same frontal areas during TM practice.
• Creates greater alpha coherence between the left and right hemispheres of the brain suggesting the brain is working as a whole.
• Enhances an individual's sense of "self" by activating what neuroscientists call the "default mode network" in the brain. (This is considered the natural ground state of the brain, glimpsed by neuroscientists during eyes-closed rest but more fully activated during Transcendental Meditation practice.)

"The finding of significant brain wave differences between students practicing the Transcendental Meditation technique and those simply resting with their eyes closed is especially convincing because subjects were randomly assigned to conditions, and testing was conducted by a researcher unaware of the experimental condition to which the subject had been assigned," said David Haaga, Ph.D., coauthor and professor of psychology at American University.

"Research has already shown that simply closing one's eyes and relaxing increases the default mode. A significant additional finding of this new study is that activity in the default mode increases during TM compared to simple eyes-closed rest," said Fred Travis, Ph.D., lead author and director of the Center for Brain, Consciousness, and Cognition at Maharishi University of Management. "Different meditation techniques entail various degrees of cognitive control. Thus, activation patterns of the default mode network could give insight into the nature of meditation practices."

In a very interesting presentation last night, Zoran Josipovic presented on the "Influence of Nondual Awareness on Anti-Correlated Networks in the Brain," which looked at meditation types and the corresponding brain activity.

The "anti-correlated networks" in that title refers to the proposal that when the brain is involved in the extrinsic network (the thalamo-cortical network) in external task processing, then the intrinsic network (the default mode network) is inactive, and the opposite is also true. When the DMN is active, the TCN is in active. All of this means the two networks are not correlated.

OK, so back to Josipovic's talk - here is the abstract:

Influence of Nondual Awareness on Anti-Correlated Networks in the Brain. Zoran Josipovic, David J. Heeger (Psychology/Center For Neursci, New York University, Center for Neural Science, New York, NY)

Globally distributed anti-correlated networks in the brain, the task-specific extrinsic and the task-negative intrinsic network, have been the focus of considerable research interest recently. Previous work has found the activity in the intrinsic system during rest to be anticorrelated with that of the extrinsic system, regions that typically exhibit response increases during goal-directed task performance. While the overall task-positive extrinsic network has been fairly well defined in relation to a variety of cognitive tasks, the full understanding of the task-negative intrinsic or default network and its functional significance has not yet emerged. Nondual awareness presents a unique opportunity to study the functioning of the intrinsic/extrinsic networks in the brain, as it is characterized by the cessation of habitual fragmenting of the field of experience into inside vs. outside, self-related vs. other-related processes. It can be described as a special case of unity consciousness in which there is no blocking of the sensory input and one is fully oriented to time and space, yet one transcends the confines of the dualistic mind. Studies of meditation indicate that these practices create lasting functional and structural changes in the brain, thus increasing our understanding of the extent of the brain’s ability to reorganize itself in response to experience. Our study seeks to contribute to this understanding by looking at the question of whether the anti-correlation between the task-positive extrinsic network and the task-negative intrinsic (default) network is an inherent property of brain organization or whether it is subject to cognitive control and learning.

Josipovic uses the terms intrinsic and extrinsic networks, rather than the default mode network and the thalamo-cortical network in his work.

His work found that in addition to the DMN and TCN opposition, there is also evidence that lateral areas of the brain are activated in non-dual states, while medial areas are activated in TM.

The most important finding in his work is that non-dual awareness synchronizes and correlates the two systems, which essentially stops the oscillation between the DMN (intrinsic system) and TCN (extrinsic system), collapsing the subject/object and self/other split that the brain generates in its daily efforts to navigate the world. Moreover, these changes, if practiced long enough, change the structure and function of the brain.

Josipovic used a variation on this graphic (From Lutz, et al, 2007) in his presentation:

Josipovic added a 5th stage based on his research, where subject, object, and reflective awareness (non-dual awareness in Josipovic's presentation) are all emphasized with the ++ designation. In his view, this is the stage of consciousness that develops in long-term non-dual practitioners.

[For an excellent overview of meditation and neuroscience, I highly recommend the chapter from Lutz linked to above.]

SUMMARY

So, the take home is that we have a default mode network in the brain that operates in the background most of the time, but is particularly active in mind-wandering and specific meditation states. We also have an extrinsic network used to solve problems, focus on tasks and related to the external world as "other."

Default mode network (DMN), also known as intrinsic network, or the subject awareness (internal focus)
Thalamo-cortical network (TCN), also known as extrinsic network, or the object awareness (external focus)

DMN is associated with Transcendental meditation, or open monitoring (OM)
TCN is associated with single-point meditation, or focused attention (FA)

In non-dual awareness, these two networks are balanced, and over the long-term, this balance becomes a stage attainment, rather than a state experience.

Tags: brain, mind, meditation, nondual awareness, Psychology, neuroscience, mind-wandering, Default mode network, DMN, intrinsic network, subject awareness, internal focus, Thalamo-cortical network, TCN, extrinsic network, object awareness, external focus, Toward a Science of Consciousness, neural networks, Zoran Josipovic, Anti-Correlated Networks, Kevin Brown, locus coeruleus, Marcus E Raichle, Brain's Dark Energy and Default Mode Networks, Antoine Lutz, Transcendental meditation, open monitoring, single-point meditation, focused attention