On Feb 26, 2008, at 5:22 PM, ruthsimplicity wrote:
>
> > However, I disagree that gamma activity is simply a matter of the
> > intellect dominating. Like some TM'ers argue that alpha activity
is of
> > major significance (not just a matter of rest) , some buddists
would
> > argue gamma activity is of major significance (not just a matter
of
> > perception).
>
> Again, look at that url. The alpha synchrony there is 100% across
a dozen or so leads. !00
> percent, as in, you can (as Fred Travis did in that illustration)
draw a vertical line with a
> ruler down the peaks of all leads...
Yes, I do not disagree on the alpha coherence. The issue is what
does it mean? And what does the gamma activity mean?
"The dominant frequency in the scalp EEG of human adults is the alpha
rhythm. It
is manifest by a ‘peak’ in spectral analysis around 10 Hz and reflects
rhythmic ‘alpha
waves’ (Klimesch, 1999; Nunez et al., 2001). Alpha oscillations are
found primarily over
occipital-parietal channels particularly when the eyes are closed, yet
alpha activity can
be recorded from nearly the entire upper cortical surface. During
wakefulness, it is a
basic EEG phenomenon that the alpha peak reflects a tonic large-scale
synchronization
of a very large population of neurons. This low-frequency global
neural activity is
thought to be elicited by reciprocal interactions between the cortex,
the reticular
nucleus and the thalamocortical (Delmonte, 1985) cells in other
thalamic nuclei
(Klimesch, 1999; Nunez et al., 2001; Slotnick, Moo, Kraut, Lesser, &
Hart, 2002) even if
cortico-cortical mechanisms also play a possible role (Lopes da Silva,
Vos, Mooibroek, &
Van Rotterdam, 1980). Because an overall decrease in alpha power has
been related to
increasing demands of attention, alertness, and task load, alpha
activity is classically
viewed as an “idling rhythm” reflecting a relaxed, unoccupied brain
(Klimesch, 1999).
Large-scale alpha synchronization blocks information processing
because very large
populations of neurons oscillate with the same phase and frequency;
thus, it is a state
of high integration but low differentiation. Within a bandwidth of
perhaps 2Hz near thisspectral peak, alpha frequencies frequently
produce spontaneously moderate to large
coherence (0.3-0.8 over large inter-electrode distance (Nunez et al.,
1997)). The alpha
coherence values reported in TM studies, as a trait in the baseline or
during meditation,
belong to this same range. Thus a global increase of alpha power and
alpha coherence
might not reflect a more “ordered” or “integrated” experience, as
frequently claimed in
TM literature, but rather a relaxed, inactive mental state (Fenwick,
1987)."
(...)
Similarly, the initial claim that TM produces a unique state of
consciousness different than sleep has been refuted by several EEG
meditation studies which reported sleep-like stages during this
technique
with increased alpha and then theta power (Pagano, Rose, Stivers, &
Warrenburg,
1976; Younger, Adriance, & Berger, 1975).
To summarize, alpha global increases and alpha coherence mostly over
frontal
electrodes are associated with TM practice when meditating compared to
baseline
(Morse, Martin, Furst, & Dubin, 1977). This global alpha increase is
similar to other
relaxation techniques. The passive absorption during the recitation of
the mantra, as
practiced in this technique, produces a brain pattern that suggests a
decrease of
processing of sensory or motor information and of mental activity in
general. Because
alpha rhythms are ubiquitous and functionally non-specific, the claim
that alpha
oscillations and alpha coherence are desirable or are linked to an
original and higher
state of consciousness seem quite premature.
--Meditation and the Neuroscience of Consciousness
Antoine Lutz, John D. Dunne, Richard J. Davidson
Cambridge Handbook of Consciousness edited by Zelazo P., Moscovitch M.
and Thompson E.
[emphases mine]
