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Sometimes
the issue in science is more fundamental than answering certain questions
about which we are ignorant. The more basic issue may be framing the question.
One remaining crucial enigma can be summed up, in the idiom of the day, as
figuring out the brain's operating system. How does the brain accomplish its
tasks from moment to moment? How does it communicate internally? How does it
combine inputs from sensory modalities into our coherent experience of the
world? How does it combine sensory experience with top-level judgments and
intention into motor output? How do emotions and feelings get into the act?
How does the brain organize hierarchies, like the hierarchy of attention?
What in the brain allows us to distinguish figure from ground? More
specifically, one might ask: How does the brain use discontinuous events, the
action potentials, to give us the subjective experience of seamless
continuity? How does the image of our world stay stable and organized in our
heads even as we move our heads, and let our eyes dart around? How does the
brain organize sequencing, the remembrance of a sequence of numbers or
words? How does the brain organize
"working memory", where we hold a thought live in our brain in
order to elaborate on it at greater length? How does the brain record into
memory even a single event in our lives?
How does the brain keep track of it all, particularly if it even
remembers what you had for lunch yesterday?
And how does it access such arcane information at will?
The importance of timing It is now clear that information encoding in the
brain cannot rely simply on the firing rate of neurons, where the brain
listens in on a neuron firing away over time and judges the level of input on
that basis. That process does happen, but it is insufficient to explain our
ability to appraise events quickly and react to them promptly. To keep us
alive, our brain has to do a lot of parallel computing. This means that
information is encoded not in individual neurons, but rather in what we call
"ensembles." In other words, a nugget of information requires a
whole raft of neurons to represent it. That, in turn, places a burden of
coordination on the brain, which must have a mechanism for preserving the
integrity of that ensemble throughout the signal processing chain. This
problem should not be underestimated, because a moment later another volley
of information comes down the pike, and it also has to be organized unto
itself. Not only that, it has to be integrated with what came before, and
with what follows. Recent discoveries in the neurosciences highlight the
centrality of that process, and postulate that the brain, in some generality,
distinguishes different ensembles, or cohorts, by
subtleties
of timing. This model is called "time binding." Some
crucial aspects of neuronal function lead naturally to such a model, although
these things are always much clearer in retrospect than in prospect. When a neuron
is stimulated by an excitatory input, a single such input is never sufficient
by itself to cause the neuron to generate an action potential and continue
the propagation of the signal. Hence, successful activation of a neuron is
always a conspiracy of events. If a neuron is considered as a voting machine,
there are always at least two people in the voting booth pulling the levers
at the same time in order for the vote to be counted. Neurons, in other
words, are coincidence detectors. This brings brain timing front and center.
We can talk about this economically by saying that the input of interest, say
from some sensory modality, is always gated, or modulated, at the synaptic
junction by another signal, which we can simply say represents the rest of the
nervous system. So, at every synaptic junction, and in every signal transfer
event, the central nervous system gets a vote! This may be a subtle
modulation, but the effect is go/no-go. This sharpens contrast down the
information processing chain, and it also sharpens the information in the
timing domain. The gating signal has a very narrow window of opportunity in
which it is able to "pass" the incoming signal. What emerges is the
realization that one of the key functions of the brain is to coordinate timing
both locally and globally, in order to facilitate communication between
different brain regions. The implication is that disruption of timing
integrity can wreak either subtle or gross malfunction of the brain.
Unfortunately, such timing is not rendered visible on all of the fancy brain
imaging techniques we have developed over the last few decades. A second key problem mentioned above is
to understand how the brain organizes continuity of experience, continuity of
its own state, and working memory, with discrete and transient events. It
apparently does so by organizing repetition. This repetition is crucial for
the organization of sensory experience. It is also crucial for those
functions that the brain uses to maintain itself from moment to moment, a
problem we may call "state management." Perhaps a kind of economy
is operative in nature, by which the same process operative in managing
sensory information and cognitive events is also used by the brain to
regulate its own affairs in considerable generality.
The Brain's Got Rhythm
The repetition of brain events imposes a requirement for a kind of strobing or reference signal that serves as a template by
means of which information is shaped in the time domain. This template may
have a local organization, concomitant with the locality of certain
information processing, or it may have a more global character, when it is
governing relationships and interactions between different brain regions. The
analogy to an orchestra comes to mind, where individual instruments have
their own locality and frequency characteristics, but each has to fit into an
overall pattern of timing and rhythmicity. An
overall harmonic structure must prevail in which the whole ensemble is
coordinated. Something along the same lines must be
going on in the brain, in which case we can assign a major role to what we
may call the "virtual conductor," the self-organizing functions in
the brain that serve to manage and coordinate this overall timing. If we must
localize this virtual conductor somewhere in the brain, it would be at the
thalamus, the grand organizer of brain timing. It is now proposed that
high-frequency repetitions organize the very transient events of sensory
experience, nuggets of cognitive activity, and specific motor acts. And it is
surmised that low frequency repetitions organize those aspects of brain
function which have longer persistence over time, such as states of
activation and arousal, the sleep-wake cycle, and perhaps even states of our
immune system and of the endocrine system. This more global role of brain
timing is gradually coming to be realized. In a treatise on how consciousness
might be understood in brain terms, Rodolfo Llinas
posited some years ago: " Attempting to
understand how the brain, as a whole, might be organized seems, for the first
time, to be a serious topic of inquiry. One aspect of its neuronal
organization that seems particularly central to global function is the rich thalamocortical interconnectivity, and most particularly
the reciprocal nature of the thalamocortical
neuronal loop function. Moreover, the interaction between the specific and
nonspecific thalamic loops suggest that rather than a gate into the brain,
the thalamus represents a hub from which any site in the cortex can
communicate with any other such site or sites". (Llinas,
1998). Dissonance What happens when
brain timing is disturbed? We have experienced an instructive experiment of
nature when Japanese children suffered seizures, nausea, and unconsciousness
following a mere five-second exposure to a rhythmically flashing light on a
TV screen. About one in 5000 children was affected. On the one hand,
scientists were not seriously shaken. They have known about "photic epilepsy" for years. But the significance of
this event--of why we are subject to photic
epilepsy--received essentially no attention. This is because the context for
that information was entirely lacking within the field of clinical neurology.
In view of what we have said above, it is quite clear that in these fragile
cases, the rhythmic stimulus could not be stabilized by the brain, and
instead it escalated into higher and higher amplitudes until a seizure
developed or consciousness was lost. This is a clear demonstration of how
utterly dependent we are on the integrity of our own brain rhythms. When that
mechanism fails, it can fail gloriously! Such failures must be a rare
phenomenon, or we would not survive as a species. Subtle failures of timing
can have effects which are somewhat less dramatic. Antonio Damasio speculated in his book, Descartes' Error, as
follows: "Any malfunction of the timing mechanism would be likely to
create spurious integration and disintegration. This may indeed be what
happens in states of confusion caused by head injury, or in some symptoms of
schizophrenia and other diseases." (p.95) Most recently, David
McCormick, who has studied the interaction between the cortex and the
thalamus with his research group for many years, asserted: Recent evidence
indicates that "dysrhythmias" cause alterations
in the normal function of the thalamocortical loop
and lead to various types of neurological disorders. Will decoding this
rhythm help us to understand the basis for movement disorders, chronic pain,
and even neuropsychological dysfunction?
A New Model for Psychopathologies
These considerations may be the opening foray into an entirely new model for
psychopathologies, a model based on deficiencies in the brain as an operating
system, and as a control system. This emerging model has much greater
richness than the present pharmacologically driven model, where the brain is
treated almost like an endocrine gland, and where the failures are attributed
to either too much or too little of one or another neuromodulator
substance. In the future, such one-dimensional models of brain function, in
which something so complex as Tourette
Syndrome or addictions is attributed to a dopamine deficit, and something so
multi-faceted as depression is reduced to a serotonin deficiency, will be
displaced with models that match the complexity of the phenomenology they are
trying to explain. Already it is becoming clear that these one-dimensional
models serve the marketing interests of the pharmaceutical companies more
than they do scientific understanding. One physiologist said he has given up
thinking that a person's well-being is determined by the amount of dopamine
floating around in his brain. And a professor of neurophysiology, in trying
to understand the role of Prozac in the brain, said that the best analogy he can
come up with is that of kicking his ancient clock radio, which had some
chance of provoking the radio into a more functional state. In other words,
the role of Prozac is not as a remedy in its own right, but as a means of
provoking the brain into a more functional state. In order to understand
this, we have to understand more than the neurochemistry of serotonin in the
brain. We have to understand the brain in its timing and bio-electrical
function.
A Remedy Tailored to the Model
Even though there is now some recognition of the need to understand
regulatory systems in their temporal properties, researchers are currently
tempted to conclude that this information will simply allow us to do better
pharmacology and more targeted surgeries. However, there is a technique that
precisely matches the problem of disregulation, and
that is simply training the brain toward improved self-regulation. We take
advantage of the fact that most of the mechanisms underlying the dysfunctions
are typically functioning at some level. We are not usually talking about an
all-or-nothing situation. If there is function at all, then it can be
discerned, and challenged to function better over the long term. This is what
neurofeedback is all about. We observe the brain in its regulatory activities
with the EEG, and we challenge the brain to change the EEG in particular
ways. By rewarding a person whenever the brain chances to move into a more
favorable state, we enhance the probability that this happenstance will be
repeated. This is known as Thorndike's "Law of Effect," which has
been a staple of biological psychology for the last century. Over time, the
brain learns the new behavior, and concomitantly we observe more regulated organismic behavior. Clinical evidence for the effectiveness
of this approach has now been found for a large variety of clinical
categories that in many instances don't appear to have much in common. The
capacity of the brain to respond to EEG-training challenges seems, therefore,
to have a broad reach over the domain of psychopathology. Such clinical
efficacy is the final link in the chain of argument that it is time to
reframe the discussion of psychopathology as primarily an issue of brain
self-regulation, and to adopt a remedy that is attuned to the problem.
Copyright, 2000, EEG Spectrum
Further Reading
Grotstein, J.S. (1986). The psychology of
powerlessness. Disorders of self-regulation and interactional
regulation as a new paradigm for psychopathology.
Psychoanalytic Inquiry, 6, 93-118
McCormick DA. Are thalamocortical rhythms the rosetta stone of a subset of neurological disorders?
Llinas R, et al. The neuronal basis for
consciousness.
Llinas RR, Ribary U, Jeanmonod D, Kronberg E, Mitra PP. Thalamocortical dysrhythmia: A neurological and neuropsychiatric
syndrome characterized by magnetoencephalography.
Proc Natl Acad Sci U S A 1999 Dec 21;96(26):15222-7
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