Szanowni Państwo,
Ponizej prezentuję fragment artykułu autorstwa p. Glyn Blackett z YORK BIOFEEDBACK CENTER. Artykuł w sposób przystępny przedstawia aspekty praktycznego zstosowania HEMOENCEFALOGRAFII oraz wyjaśnia kluczowe pojęcia teoretyczne
Z Szacunkiem
Dariusz Wyspiański
"Hemoencephalography:
A New Form of Neurofeedback
Glyn Blackett
YORK biofeedback CENTRE
Introduction Neurofeedback is a means of training brain
functioning, either to ameliorate symptoms of a
disorder or to improve performance.
The trainee is presented with some measure of
brain activity, and tries to influence the signal in a
desired direction. Figure 1 shows a graph
obtained during a neurofeedback training session.
What specifically to we mean by activity and how
do we measure it? In “traditional” neurofeedback
we monitor the brain’s electrical activity - called
the electroencephalograph.
Hemoencephalography (HEG) is a more recent
development which is based on a different way of
quantifying brain activity.
The Physiological Basis of HEG
One way to quantify brain activity is in terms of
metabolic activity or metabolic rate. In fact this
concept has widespread applicability in the field
of neuroimaging. Metabolism is a cellular process
in which “fuel” in the form of glucose or sugar is
“burned” to release energy for use by the cell.
The process consumes oxygen and creates carbon
dioxide. Metabolic rate is the rate at which energy
is used up.
When the brain is engaged in some mental task
such as mental arithmetic, we expect that those
regions of the brain directly involved in the task
will use energy at a faster rate than other regions.
The human brain is extremely metabolically
active. Although the brain makes up just 2% of
body weight, it accounts for 20% of the body’s
oxygen consumption and 25% of glucose
consumption.1 In order to meet this energy
demand, brain tissue has an extremely dense
network of blood vessels and capillaries.
How do we measure metabolic rate? We can
measure it indirectly, in a number of ways. Some
of these ways rely on a phenomenon known as
neurovascular coupling.
Neurovascular Coupling
Metabolic activity depends upon a supply of
glucose and oxygen, which arrive via the
bloodstream. Neurovascular coupling is a
mechanism for matching blood flow to metabolic
demand in the brain. This means that whenever
there is a localised increase in neural activity
(which happens when the brain engages in some
specific mental task) there is a rapid localised
increase in cerebral blood flow. A consequence of
this response is that the blood in the active region
becomes more oxygenated (i.e. the concentration
of oxygen increases).
The process is managed by cells called astrocytes
- these are a common type of glial cell or support
cell in the brain.
Brain Scanning
There are two broad classes of brain scanners -
those that reveal structure and those that look at
activity. Here we’re concerned with the latter.
These scanners indirectly measure metabolic
activity. Typically they’re used in research to try
to infer which regions of the brain are involved in
particular tasks.
PET2 & SPECT3 measure the relative rates at
which glucose (the brain’s fuel) is used up.
Glucose which has been tagged with radioactive
atoms is injected into the subject’s bloodstream.
The fate of this glucose is tracked by measuring
the radiation it emits. Relatively more of it is
delivered to the more active regions of the brain.
Functional MRI or fMRI4 detects the localised
increases in blood oxygenation mentioned above.
This increase in oxygenation level changes the
magnetic properties of the blood, and this change
can be detected when the brain is subjected to a
strong magnetic field.
HEG
Like fMRI, HEG also detects changes in brain
activation by detecting changes in blood
oxygenation.
Let’s summarise the process:
A mental task activates neurons in some
particular region of the brain.
These neurons consume relatively more
energy
This demand for energy is met by a localised
increase in blood flow.
The local oxygenation level of the blood
increases.
There are actually two forms of HEG, each form
having its own sensor. They measure different
aspects of the one process (metabolic activation),
and hence have a similar range of appication and
achieve similar results.
Near Infra-Red HEG
Near infra-red (NIR) HEG is historically the first
form. It was invented by Dr Hershel Toomim. He
adapted a method called Infra-red Spectroscopy.
His original contribution was to realise that the
signal he was measuring could be consciously
influenced and hence was useful in a context of
biofeedback training.
The NIR device shines a light source into the
head, most typically at the forehead (in part
because hair obstructs the signal). The light is a
mixture of red and infra-red wavelengths. A
proportion of this light is bounced back out by a
physical process called scattering. The device
then measures this scattered light.
This is possible because the scalp, skull and brain
matter (both grey and white) are relatively
translucent to light of this wavelength. Blood,
however, is not. Furthermore, the proportions of
the light absorbed and scattered by blood depend
on its level of oxygenation. This means that as the
local oxygenation level of blood increases in
response to neural activation, the signal from the
device changes. Thus the device can detect
changes in the brain’s activation level.
Dr Toomim found a very good correlation
between his device and fMRI, which also relies
upon changes in blood oxygenation.5
The device can’t give absolute measurements of
activity. The signal is affected by factors such as
skull thickness - so we can’t compare one person
to another. But it can detect changes happening
over a short time scale, which is all we need in
order to be able to train activation.
The current generation of NIR HEG sensor only
detects activity in the brain’s outer layer - the
cortex. It is possible that future developments
may allow training of structures much deeper in
the brain.
Passive Infra-Red HEG
Passive Infra-Red or PIR HEG is conceptually
much simpler. It was invented by Dr Jeffrey
Carmen, who adapted a technique called
thermoscopy. The sensor detects light (or
electromagnetic radiation) of a particular
wavelength - a small band within the infra-red
(IR) part of the spectrum. This IR radiation is
essentially heat being radiated by the brain. The
sources are firstly local metabolic activity (sugar
being burned for energy release) and secondly,
local blood flow. This heat is detected in other
forms of thermal imaging - in fact thermal
cameras have been used to assess the effects of
HEG training - see figure 2.
Comparison with EEG Neurofeedback
Compared to EEG neurofeedback HEG has these
advantages:
The signal is much simpler to interpret: it
either increases or decreases in magnitude
(corresponding to increases and decreases in
brain activation, respectively).
The signal is more stable (EEG measures tend
to fluctuate rapidly and seemingly quite
randomly)
The signal is much less subject to
contamination by artefact.
Dr Toomim claims that clinical benefits are
achieved more rapidly.
Training HEG
In HEG neurofeedback, the trainee tries to
increase the signal, which is equivalent to
activating the region of the brain under the
sensor. To achieve this (at least for the forehead
placement) the trainee looks for:
an intensely alert or awake state of mind
a firm intention or desire that the signal
increase, but at the same time
a relaxed, open, emotionally positive state -
not getting too hooked into getting results
because frustration tends to lead to
deactivation.
Applications of HEG Neurofeedback
HEG is still a new neurofeedback modality and
much work needs to be done in researching the
applications. Here I’ll consider three areas where
HEG is already proving itself:
ADD
Depression
Migraine
The Prefrontal Cortex
One thing that links these disorders is the
possibility of dysregulation of the Prefrontal
Cortex (PFC).
The PFC is the region of the cortex (outer layer of
brain) behind the forehead, and also above the
eyeballs (on the underside of the brain). The PFC
is a particularly important part of the brain, most
highly evolved in humans, and sometimes
described as the brain’s executive control centre7.
It plays a central role in purposive behaviour -
making decisions, formulating and carrying out
plans and intentions, and sticking to them in the
face of distracting stimuli. It coordinates the brain
resources needed to carry out these intentions,
and evaluates actions in terms of their success or
failure in meeting objectives.
For instance, suppose one day it is time for your
evening meal. You’ll formulate a plan for
meeting that need - you decide to cook a meal,
and then decide what to cook. The PFC is
responsible for formulating the steps needed to
meet this goal - e.g. first get the pans and utensils
out. The PFC accesses the knowledge you need -
for example your memory of where you keep
your pans. Suppose the phone rings while you’re
cooking - you decide to answer it, but hold your
intentions in mind so that you can come back to
cooking when you’re finished on the phone.
The PFC is also strongly linked to motivation and
emotion (these are of course connected). You can
keep to a long-term plan (e.g. gaining a degree)
by somehow holding in mind the good feelings
connected to achieving that goal.
The PFC has the ability to inhibit other structures
in the brain connected to emotions, enabling you
to for example override a fear of heights when
you need to climb a ladder.
Emotions are connected decision-making - it
seems that the PFC arrives at decisions by in
some way “imagining” the feelings that would
result from each option.8
The PFC is especially relevant to social emotions
because our ability to imagine what other people
are thinking and feeling depends upon the PFC.
Figure 2: Images taken with a thermal camera, before (left) and after (right) a single
session of HEG training. The subject has AD/HD. Note the increase in temperature
seen over the whole forehead. Images courtesy of Dr. Robert Coben.
ADD
The behaviours described in the preceding section
are just those that people with ADD find difficult
- in short their problems are distractibility,
impulsiveness, disorganisation, short attention
span and quite commonly emotional difficulties
too.
ADD is a real neurological disorder, and typically
results in dysregulation of the PFC. The root of
the problem may lie in other parts of the attention
system (which includes many areas in the brain) -
for example the dopamine pathway that acts
something like the PFC’s power supply. PFC
function seems to be relatively easily
dysregulated since it is at the top of the brain’s
organisational tree.
Brain scanning studies have shown difficient
activty in the PFC of ADD sufferers, and is
sometimes seen to deactivate further during tasks
requiring concentrated attention, for which you
would normally see an increase in PFC activity.
Though still a new form of therapy, HEG
neurofeedback is showing promising results for
ADD.
Depression Depressed people typically suffer from
diminished energy and motivation and poor
focus. Some experience emotional flatness, others
strongly painful emotions. All these symptoms
can be linked to dysregulation in the PFC.
Training increased activity in the PFC can be a
good idea for depression, firstly because it’s often
under-active9, and secondly since it plays a role in
regulating other emotional centres in the brain.
As with ADD, the PFC dysregulation may be
contingent upon problems somewhere else in the
brain, but that need not undermine the potential
benefit of training PFC activation.
Migraine Dr Jeffrey Carmen developed PIR HEG
specifically to treat migraine, with encouraging
results. He treated 100 migraineurs with PIR
HEG over a four-year period.10 Over 90% of
subjects who completed at least 6 sessions
reported significant improvement in migraines.
‘Significant improvement’ was the point at which
it became difficult to identify headaches as
migraines - i.e substantially reduced pain levels.
Typically both pain levels and frequency of
migraine improved. (24 people dropped out of
therapy before 6 sessions for various reasons
including financial.) 61% experienced significant
improvement after six sessions or less.
The underlying neuropathology of migraine
remains unknown. Dr Carmen’s theory for the
efficacy of PIR HEG is that training strengthens
the PFC’s inhibitory control over some part of the
brain stem thought to generate migraines..."
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