together? We do not yet know, but there are some indications
that the unified whole appears by virtue of the temporal fine-structure
characterizing the conscious brain’s activity—that is, the rhythmic
dance of neuronal discharges and synchronous oscillations. This is why
the border of this whole is a functional border, outlining the island of
consciousness in an ocean made up of a myriad of less integrated and
less densely coupled neural micro-events. Whatever information is
within this cloud of firing neurons is conscious information. Whatever is
within the cloud’s boundary (the “dynamical core”) is part of our inner
world; whatever is outside of it is not part of our subjective reality. Conscious
experience can thus be seen as a special global property of the
overall neural dynamics of your brain, a special form of informationprocessing
based on a globally integrated data format.
We also possess the first mathematical instruments that allow us to
describe the causal complexity within the dynamical core of consciousness.
Technical details aside, they show us how self-organization in our
brains strikes an optimal balance between integration and segregation,
creating the wonderful richness and diversity of conscious contents and
the unity of consciousness at the same time.
What does all this mean? What we want for consciousness is not a
uniform state of global synchrony, a state in which many nerve cells
simply fire together simultaneously. We find such uniformity in states
of unconsciousness such as deep sleep and during epileptic seizures; in
these cases, the synchrony wipes out all the internal complexity: It is as
if the synchrony had glossed over all the colors and shapes, the objects
making up our world. We want large-scale coherence spanning many areas of the brain and flexibly binding many different contents into a
conscious hierarchy: the letters into the page, the page into the book,
the hand holding the book into your bodily self, and the self sitting in a
chair in the room and understanding the words. We want a unity of consciousness
that—internally—is as differentiated as possible. On the
other hand, maximal differentiation is not optimal, either, because then
our world would fall apart into unconnected pieces of mental content
and we would lose consciousness. The trick with consciousness is to
achieve just the right trade-off between the parts and the whole—and at
any single moment a widely distributed network of neurons in the brain
seems to achieve just that, as a cloud of single nerve cells, dispersed in
space, fire away in intricate patterns of synchronous activity, perhaps
with one pattern becoming embedded in the next. Just like the water
droplets that form a real cloud, some elements leave the aggregate at any
given moment, while others join it. Consciousness is a large-scale, unified
phenomenon emerging from a myriad of physical micro-events. As
long as a sufficiently high degree of internal correlation and causal coupling
allows this island of dancing micro-events in your brain to emerge,
you live in a single reality. A single, unified world appears to you.
This emergence can happen during “offline states” as well: In dreams,
however, the binding of contents does not work quite as well, which is
why your dream reality is frequently so bizarre, why you have difficulty
focusing your attention, why scenes follow each other so quickly. Nevertheless,
there is still an overall situation, you are still present, and that is
why phenomenal experience continues. But when you move into deep
sleep and the island dissolves back into the sea, your world disappears as
well. We humans have known this since Greek antiquity: Sleep is the little
brother of death; it means letting go of the world.
One of the intriguing characteristics of current research into consciousness
is how old philosophical ideas reappear in the best of cutting-
edge neuroscience—in new disguise, as it were. Aristotle and Franz
Brentano alike pointed out that consciously perceiving must also mean
being aware of the fact that one is consciously perceiving, right now, at
this very moment. In a certain sense, we must perceive the perceiving
while it happens. If this idea is true, the brain state creating your con-scious perception of the book in your hand right now must have two
logical parts: one portraying the book and one continuously representing
the state itself. One part points at the world, and one at itself. Conscious
states could be exactly those states that “metarepresent”
themselves while representing something else. This classical idea has
logical problems, but the insight itself can perhaps be preserved in an
empirically plausible framework.
Work being done by Dutch neuroscientist Victor Lamme in Amsterdam
and in Stanislas Dehaene’s lab at the NeuroSpin Center in the CEA
campus of Saclay and at the Pitié-Salpêtrière Hospital in Paris converges
on the central importance of so-called recurrent connections as a functional
basis for consciousness. In conscious visual processing, for example,
high-level information is dynamically mapped back to low-level
information, but it all refers to the same retinal image. Each time your
eyes land on a scene (remember, your eye makes about three saccades
per second), there is a feedforward-feedback cycle about the current image,
and that cycle gives you the detailed conscious percept of that
scene. You continuously make conscious snapshots of the world via
these feedforward-feedback cycles. In a more general sense, the principle
is that the almost continuous feedback-loops from higher to lower
areas create an ongoing cycle, a circular nested flow of information, in
which what happened a few milliseconds ago is dynamically mapped
back to what is coming in right now. In this way, the immediate past
continuously creates a context for the present—it filters what can be experienced
right now. We see how an old philosophical idea is refined
and spelled out by modern neuroscience on the nuts-and-bolts level. A
standing context-loop is created. And this may be a deeper insight into
the essence of the world-creating function of conscious experience:
Conscious information seems to be integrated and unified precisely because
the underlying physical process is mapped back onto itself and
becomes its own context. If we apply this idea not to single representations,
such as the visual experience of an apple in your hand, but to the
brain’s unified portrait of the world as a whole, then the dynamic flow of
conscious experience appears as the result of a continuous large-scale
application of the brain’s prior knowledge to the current situation. If you are conscious, the overall process of perceiving, learning, and living creates
a context for itself—and that is how your reality turns into a lived
reality.
Another fascinating scientific route into the One-World Problem is
increasingly receiving attention. It has long been known that in deep
meditation the experience of unity and holistic integration is particularly
salient. Thus, if we want to know what consciousness is, why not
consult those people who cultivate it in its purest form? Or even better,
why not use our modern neuroimaging techniques to look directly into
their brains while they maximize the unity and holism of their minds?
Antoine Lutz and his colleagues at the W. M. Keck Laboratory for
Functional Brain Imaging and Behavior at the University of Wisconsin
studied Tibetan monks who had experienced at least ten thousand
hours of meditation. They found that meditators self-induce sustained
high-amplitude gamma-band oscillations and global phase-synchrony,
visible in EEG recordings made while they are meditating. The highamplitude
gamma activity found in some of these meditators seems to
be the strongest reported in the scientific literature. Why is this interesting?
As Wolf Singer and his coworkers have shown, gamma-band oscillations,
caused by groups of neurons firing away in synchrony about
forty times per second, are one of our best current candidates for creating
unity and wholeness (although their specific role in this respect is
still very much debated). For example, on the level of conscious objectperception,
these synchronous oscillations often seem to be what makes
an object’s various features—the edges, color, and surface texture of, say,
an apple—cohere as a single unified percept. Many experiments have
shown that synchronous firing may be exactly what differentiates an assembly
of neurons that gains access to consciousness from one that also
fires away but in an uncoordinated manner and thus does not. Synchrony
is a powerful causal force: If a thousand soldiers walk over a
bridge together, nothing happens; however, if they march across in lockstep,
the bridge may well collapse.
The synchrony of neural responses also plays a decisive role in figurebackground
segregation—that is, the pop-out effect that lets us perceive
an object against a background, allowing a new gestalt to emerge from the perceptual scene. Ulrich Ott is Germany’s leading meditation researcher,
working at the Bender Institute of Neuroimaging at the Justus-
Liebig-Universität in Giessen. He confronted me with an intriguing
idea: Could deep meditation be the process, perhaps the only process, in
which human beings can sometimes turn the global background into the
gestalt, the dominating feature of consciousness itself? This assumption
would fit in nicely with an intuition held by many, among others Antoine
Lutz, namely that the fundamental subject/object structure of experience
can be transcended in states of this kind.
Interestingly, this high-amplitude oscillatory activity in the brains of
experienced meditators emerges over several dozens of seconds. They
can’t just switch it on; instead, it begins to unfold only when the meditator
manages effortlessly to “step out of the way.” The full-blown meditative
state emerges only slowly, but this is exactly what the theory
predicts: As a gigantic network phenomenon, the level of neural synchronization
underlying the unity of consciousness will require more
time to develop, because the amount of time required to achieve synchronization
is proportional to the size of the neural assembly—in meditation,
an orchestrated group of many hundreds of million nerve cells
must be formed. The oscillations also correlate with the meditators’ verbal
reports of the intensity of the meditative experience—that is, oscillations
are directly related to reports of intensity. Another interesting
finding is that there are significant postmeditative changes to the baseline
activity of the brain. Apparently, repeated meditative practice
changes the deep structure of consciousness. If meditation is seen as a
form of mental training, it turns out that oscillatory synchrony in the
gamma range opens just the right time window that would be necessary
to promote synaptic change efficiently.
To sum up, it would seem that feature binding occurs when the widely
distributed neurons that represent the reflection of light, the surface
properties, and the weight of, say, this book start dancing together, firing
at the same time. This rhythmic firing pattern creates a coherent cloud in
your brain, a network of neurons representing a single object—the
book—for you at a particular moment. Holding it all together is coherence
in time. Binding is achieved in the temporal dimension. The unity of consciousness is thus seen to be a dynamic property of the human brain.
It spans many levels of organization, it self-organizes over time, and it
constantly seeks an optimal balance between the parts and the whole as
they gradually unfold. It shows up on the EEG as a slowly evolving global
property, and, as demonstrated by our meditators, it can be cultivated
and explored from the inside, from the first-person perspective. Please
also see the interview with Wolf Singer at the end of this chapter.
But the next problem in formulating a complete theory of consciousness
is more difficult.
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