You said:
In fact, it is almost impossible at this time to get the level of resolution in real time that is required to track brain activity in the way that you describe.
eLORETA is an EEG analysis practice based on how sonar-location is done. It looks at multiple sources of EEG simultaneously and basically "triangulates" the source of a given signal. While not perfect you can make a few assumptions (like signals aren't coming from outside the brain and by using a sphere to estimate electrode placement) to make things more accurate.
The analysis done to produce this spectacular video https://www.youtube.com/watch?v=6Sz-l6RDrvU is done using actual fMRI of a specific person to specify the exact location of the electrodes for the EEG analysis. The mathematical analysis and the number of electrodes used are different than the eLORETA analysis used in the TM studies, but the basic process is the same.
The downside is that spatial resolution is far less than with fMRI, but the sampling rate is correspondingly greater (there's a tradeoff between spatial and temporal resolution when you use fMRI vs EEG -they used both for that video, as they explain):
https://www.youtube.com/watch?v=6Sz-l6RDrvU
[TM researchers someday hope to get similar videos done to illustrate the "pure consciousness" state during TM -see below for more details concerning that state]
You said:
However, I am not aware of any literature that discusses the effects you are describing for the default mode network. Additionally, I am not aware of any papers that describe the chain of events you describe.
The two studies mentioned by Jim Karpen explicitly mention the DMN in some way. The first says "Greater activation in areas that overlap the DMN during TM practice suggests that..." which is more than a "suggestion."
The second paper was performed and specifically titled the way it is *because* mindfulness and concentration readers actually read the first paper and mis-cited it, claiming that it supports *their* claim that all meditation practices reduce the activity of the DMN. That mindfulness review paper is: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4054695/
Citation #98 is the first paper that Jim mentioned. Obviously "greater activation" is not "reduced activation," but that is how the paper is cited. When I pointed this situation out to the lead author of that TM study, he gave the email equivalent of an eye-roll.
Later, he and a student did the second study Jim mentioned and titled it the way that he did to try to make sure that his work isn't mis-cited (its hard to say that the title is misleading, even if you can somehow justify confusing "greater" and "reduced" in the abstract).
There are quite a few studies on TM and EEG. The most common finding is that EEG coherence in the alpha frequencies in the frontal lobes is enhanced during TM. Note that this is the same EEG signature where eLORETA analysis found "Greater activation in areas that overlap the DMN during TM practice," so it isn't that big a stretch to assume that the other studies also support "greater activation" of the DMN, even if only indirectly.
Meanwhile, research finds that EEG coherence, in general, between most areas of the brain (not just the frontal lobes) is reduced during most other meditation practices besides TM:
https://www.ncbi.nlm.nih.gov/pubmed/22266174
"The globally reduced functional interdependence between brain regions in meditation suggests that interaction between the self process functions is minimized, and that constraints on the self process by other processes are minimized, thereby leading to the subjective experience of non-involvement, detachment and letting go, as well as of all-oneness and dissolution of ego borders during meditation."
Note that this is the exact *opposite* of what is found during and outside of TM: not only is EEG coherence enhanced in the frontal lobes during TM, but consistently outside of TM, with the most-consistent and greatest EEG coherence being found in the frontal lobes of the "enlightened" subjects -see figure 1:
http://www.totalbrain.ch/wordpress/wp-content/uploads/2007/05/brain-int…
I used the word "enlightenment" above. In the TM lexicon, the first stage of enlightenment is when a "pure" (not associated with specific things) sense-of-self starts to emerge, and eventually become permanent, present whether one is awake, dreaming, or in deep sleep. The subjects in the following paper (and in the one above) were chosen specifically because they reported this "permanent sense-of-self" being present (even during deep sleep) continuously for at last a year:
http://www.totalbrain.ch/wordpress/wp-content/uploads/2007/05/eeg-of-en…
Unlike other forms of meditation, TM practice does NOT reduce the activity of the DMN, nor does it reduce EEG coherence during practice, but rather enhances it, at least in the frontal lobes. This goes directly to "sense of self" issues, as it is the activity of the brain's default mode network that is thought to give rise to sense of self. In most people, sense-of-self is associated with what might be called a "noisy" DMN. In long-term meditators of other practices, sense-of-self is *reduced*. That was the desired outcome in the spiritual traditions where these practices originated. With TM, the activity of the DMN is NOT reduced, but the signature "coherent alpha-1 activity" suggests that simple connectivity between the parts of the DMN is being enhanced. This would explain the internal perception that sense-of-self is NOT associated with "things" or mental activities, but merely is:
"When I say 'I' that's the Self. There's a quality that is so pervasive about the Self that I'm quite sure that the 'I' is the same 'I' as everyone else's 'I.' Not in terms of what follows right after. I am tall, I am short, I am fat, I am this, I am that. But the 'I' part. The 'I am' part is the same 'I am' for you and me" [see Table 3 in paper directly above].
The discussion of those papers and the theory that explains them is found in this review paper:
https://www.researchgate.net/profile/Frederick_Travis/publication/26118…
The assumption is that all of TM can be understood as a cycle of reducing mental activity in the direction of complete cessation of all perception, both internal and external, followed by a period of increased activity. The period of complete cessation of all perception, both internal and external, is called _samadhi_ in Sanskrit, or "pure consciousness" in TM-speak. These papers are studying specifically those periods, if/when they occur during TM. The subjects were selected *specifically* because they reported that they had regular episodes of this _samadhi_ state, so these aren't random controlled studies, but rather careful analysis of specific case subjects (You will need to provide a CAPTCHA word in English—just ignore the Russian—to read these full text pdf files):
http://cyber.sci-hub.bz/MTAuMTA5Ny8wMDAwNjg0Mi0xOTgyMDUwMDAtMDAwMDE=/10…
http://www.sante-conscience.fr/medias/Badawi_etal_1984.pdf
http://moscow.sci-hub.bz/c2e2fb65ea1b248b35027494ddc4053c/10.1097%40000…
http://moscow.sci-hub.bz/7e79cb20aa45e1cf35d4b37885e8d68f/10.1111%40j.1…
The most consistent EEG finding is: increased alpha-1 coherence in the frontal lobes during compared to outside of the _samadhi_ state during TM.
The most *dramatic* finding, and one that has been noted in spiritual and mystical literature for thousands of years, is the apparent cessation of breathing. Note that this has NEVER been observed in mindfulness or concentration subjects. Before Maharishi brought meditation out of the monastery in 1957, the tradition was that only an enlightened guru/teacher could properly teach meditation. The carefully choreographed, carefully rehearsed teaching play that TM teachers perform over four days was Maharishi's answer: in that carefully contrived context, he attempted to train people to literally "play the part" of an enlightened guru.
The difference, some people consistently showing _samadhi_ when they learn TM vs no-one in 5,000 studies on other forms of meditation ever showing the breath suspension state, suggests that the teaching play makes all the difference:
it isn't just "what" is taught, but *how* it is taught, that is important.
Consider these two pilot studies on TM taught to war refugees living in tent cities or even under bushes:
http://www.ptsdreliefnow.org/the-research.html
Compare those findings with the typical findings for mindfulness practice. There's a reason why the United Nations is doing its own research to see if they want their own disaster relief workers trained *as* TM teachers.
Similar studies are being conducted around the world after the David Lynch Foundation taught literally hundreds of thousands of school kids for free and invited the nations of the world to evaluate the results.
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TM is a simple, easy-to-learn, literally effortless practice. We can prove that it is effortless on a physiological level, because the activity of the brain's DMN is not reduced during practice, unlike virtually every other meditaiton practice that has been studied. Further, since the long-term finding is that the EEG activity of any form of meditation starts to become a trait found outside of meditation, the implication is that TM does NOT interfere with the activity of the DMN, while other practices do.
This might suggest that any benefit from meditation that is due to resting will tend to disappear over time in other practices as they become progressively less restful as people get "better" at them.
In 2013, the American Heart Association reviewed all available research and found explicitly that only TM had robust enough research with consistent enough effects that they could say to doctors that they might recommend TM to their patients as an adjunct (secondary) therapy for the treatment of hypertension, while all other meditation practices did NOT receive that recommendation (see page 6 for TM vs mindfulness and page 8 for relaxation techniques including the Relaxation response):
http://hyper.ahajournals.org/content/hypertensionaha/early/2013/04/22/H…
The only head-to-head study of TM, some kind of mindfulness and the Relaxation Response, that I am aware of is this paper:
https://www.ncbi.nlm.nih.gov/pubmed/2693686
Note that this is NOT MBSR. However, the "low mindfulness relaxation" was basically the Relaxation Response.
The only longitudinal study on mindfulness (MBSR) that I am aware of is: https://www.ncbi.nlm.nih.gov/pubmed/24798861
"Parallel to the reduction of stress levels after 1 year, the intervention-group additionally showed reduced catecholamine levels (p 0.05), improved 24 h-mean arterial (p 0.05) and maximum systolic blood pressure (p 0.01), as well as a reduction in IMT (p 0.01). However, these effects were lost after 2 and 3 years of follow-up."
Note that this supports my assertion that practices that reduce the activity of the DMN will NOT show long-term benefits due to rest -in a very real sense, these practices train the brain to NEVER rest.
The only long-term study on the Relaxation Response (see head-to-head study) found that there was no real effect on blood pressure from that practice.
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Trying to say that all meditation practices are the same is NOT supported.
Incidentally, the only way to fully resolve this issue is, as the American Heart Association points out, to do head-to-head studies. For the past few years, the TM resaerchers I know have been trying to get mindfulness researchers to collaborate in a head-to-head study similar to that study that was done almost 30 years ago. No-one is willing to collaborate to do such a study. People accuse TMers of being religious, but look at the title of that research review on other forms of meditation, written by the most prominent meditation researchers (other than TM). Most mindfulness researchers are Buddhists, and many BUddhists sincerely believe that the sense-of-self-enhancing effects of TM are anti-Buddhist and so won't participate in any study thta might show TM in a good light.