We understand quite a lot of how the brain works, but there is
still an
awful lot we don't know about brain functions.
Because of its complexity and delicate nature,
investigation brain function is tricky and difficult to do without great
caution (its like a thick jelly).
To investigate brain function we need to 'get inside' the brain and
observe in some direct, but safe way, and preferably not by surgical
methods - cutting the skull open to examine brain tissue carries a high
risk of permanent brain damage!
Much has been learned historically from people who have
suffered in some small way with brain damage - in other words damage
to one small part of the brain.
The effect of this brain damage on the patient can tell a
clinician what the function of the damaged part of the brain was
responsible for.
e.g. if an area at the back of the brain was damaged by a stroke
and the patient went blind, you would know that part of the brain
was involved with vision.
A stroke in the brain stem or cerebellum of a patient can affect
breathing and heartbeat. It can also cause speech impairment,
hearing and cause vertigo (difficulty in balancing).
People who have suffered massive brain injury, but survive, would
give us some insight, but, would it be ethical to study someone who
might not be in a position to grant (informal consent) the brain
investigation?
You can study the brains of people who have died - in your will
or donor card system, you can leave parts or all of your body for
medical research.
You can push tiny electrodes into brain tissue and give it
a tiny electrical stimulus.
You can then observe what happens on
stimulating various parts of the brain.
You can then relate that part of
the brain with what happens.
e.g. If you stimulate the part of he brain called the motor area,
it causes muscle contraction and movement.
An electroencephalogram (EEG) is
a test that detects electrical activity in your brain using small,
metal discs (electrodes) attached to your scalp - the electrodes
pick up patterns of electrical activity in the brain.
Your brain cells communicate via
electrical impulses and are active all the time, even when
you're asleep. With electroencephalography you can monitor this
activity, which shows up as wavy lines on an EEG recording.
Non-invasive scanning-mapping
techniques external to the body
The advancement in new technology is helping academics research
the brain with plenty of spin-offs to help patients with brain
conditions. We can now examine the brain without intrusive surgery using
various 'high-tech' scanning machines.
A magnetic resonance imaging scanner (MRI machine) is
a complex and costly way of producing a very detailed picture of the
brain's structure.
MRI uses strong magnetic fields and radio
waves to produce a highly detailed image of the nervous system
of the brain (and any other part of the body too).
You can monitor the brain's activity while a person is doing
particular things e.g. solving a problem, doing a skilled or
unskilled physical task or doing a memory test and while they
are enclosed in the MRI scanner.
An fMRI scanner (functioning magnetic resonance imaging) is a
more advanced MRI scanner which is able to detect increased
blood flow in the activated areas of the brain, an MRI scanner
cannot.
MRI is a very safe non-invasive technique
that doesn't use ionising radiation, so safer than CF scanning
and PET scans (both briefly described next).
A
CT scanner uses X-rays to produce an image of the
main structures of the brain.
However, a CT scanner cannot show the functioning of the
imaged parts of the brain.
BUT, the CT scan can show a damaged or diseased part of the
brain which can be related to some loss of function by the
patient.
e.g. loss of mobility or loss of vision can be related to
damaged areas of the brain in the CT scanner image.
PET scanners are much more sophisticated and involve
the use of radioactive tracer
Positron emission tomography (PET) scans
are used in medicine to produce highly detailed
three-dimensional images of the inside of the human body.
PET
images can clearly show the part of the body being investigated
e.g. brain function,
including any abnormal behaviour.
The patient is injected with a
radioisotope, whose emitted radiation is monitored by detection
screens. The radioisotope (radioactive tracer) atom is
incorporated in a molecule that moves around the body e.g. a
derivative of glucose. This molecule accumulates in more active
cells.
You can actually monitor the patient's brain activity
while they are in the PET scanner.
The PET scan can show which parts of the
brain are active and behaving normally or abnormally - unusual
reduced activity or not functioning at all.
PET scans are so detailed you can
investigate brain structure in real time and see how the
patient's brain is
functioning while they are in the PET scanner.
This means PET scans can be used to study
disorders that change the brain's activity like Alzheimer's
disease.
Here, certain parts of the brain become less active
e.g. the memory region, and
the PET scan can be compared with that of a normal brain.
For more details on pet scans see
Uses of radioactive isotopes
in medicine
PET scans are often combined
with computerised tomography (CT) scans to produce even more
detailed 3D images, known as PET-CT scans.
PET scans may also
occasionally be combined with a magnetic resonance imaging (MRI)
scan, known as a PET-MRI scan.
Techniques are getting increasingly
sophisticated and costly, but all for the patient's benefit.
Transcranial magnetic stimulation (TMS) uses a
magnetic field to change brain activity in targeted areas of the
brain.
TMS uses magnetic fields to stimulate
selected nerve cell activity and has been used to treat
depression.
Footnotes on scanners: Despite the
wonderful technology, interpreting these scans for diagnostic
purposes is not always clear cut i.e. it can inform to help in a
prognosis and affect a treatment decision, but its not always that
'simple'.
One problem is that the brain function
observed in the scanner, might not be what you would
'theoretically' observe in real life outside the scanner. The
mere fact that you are lying down and enclosed inside the
scanner means you are not in an everyday state!
Another problem is that our knowledge is
still inadequate in knowing how treat certain brain conditions
and we cannot adequately access some areas of the brain - so
test results can be hard to fully interpret for the benefit of
the patient.
For more see the
uses of radioactive
materials in medicine notes
