Download Direct Electrode Stimulation Direct electrode stimulation involves

Direct Electrode Stimulation
Direct electrode stimulation involves using a device that emits weak electric current to activate or
disrupt the normal activity of neurons in a specific brain area. This nature of this procedure is that a
patients skull is cut into two, allowing the surgeon access to the brain to then use an electrode to
stimulate different areas of the brain and record the results of each brain function. An example of
this is by Wilder Penfield who performed these studies in the 1940’s to 1960’s to direct brain
stimulation. The advantages of this procedure is that it allows research on the brains function, and
disadvantages are that it is very invasive, imposes risks and is unacceptable by today’s ethical
standards.
Single Pulse TMS
Transcranial magnetic stimulation is a direct brain stimulation technique that delivers a magnetic
field pulse through the skull and temporarily activates or disrupts the normal activity of neurons in a
specific area of the cerebral cortex. In this procedure, patients are sat in a chair while a magnetic
field pulse is transmitted from a small copper electromagnetic coil placed next to the scalp. The
single pulse activates neurons and they send a burst of neural impulses (electrical activity) to
adjacent neurons, to activate an area of the cerebral cortex. The advantages of single pulse TMS is
that it is non-invasive, safe and harmless, no anaesthetic, x-rays and radioactive substances are used.
Disadvantages of single pulse TMS are that it cannot be used on patients with metal or implanted
medical devices in their body or if they have a history of seizures, and also if the researcher
stimulates at the wrong time, it will not activate electrical activity to cerebral cortex.
rTMS
Repeated TMS is the exact same procedure except this type of direct brain stimulation involves the
repeated, but not rapid delivery of a pulse to the brain. When rTMS is used the consecutive pulses
causes the neurons to lose their ability to fire, this is used to make specific brain areas inactive to
measure temporary changes in all kinds of behaviour and mental processes. It can be used to study
how the brain organises different functions such as language, memory, vision or attention.
Advantages are the same of an TMS. Disadvantages are also the same as TMS although 30% of
patients do incur headaches at the site of stimulation.
EEG
An electroencephalograph is a device that detects, amplifies and records general patterns of
electrical activity of the brain. This procedure is undertaken by numerous small electrodes pasted to
the surface of the scalp at the top and sides of the head. Results are translated into brainwaves and
displayed on a graph to visually show the pattern, frequency and amplitude of your brainwaves.
Advantages of this are the ability to determine the level of consciousness and style of brainwaves
produced by a patient to compare with their brain. Disadvantages include are that this is only limited
to these advantages and nothing further.
CT
Computerised tomography is a neuroimaging technique that produces a computer enhanced image
of a cross section (‘slice’) of the brain from x-rays taken from different angles. This procedure
involves moving an x-ray source in an arc around the head while a computer compiles different
‘snapshots’ of the brain area. In this procedure the patient is first given an injection of a substance of
contrast (iodine) into the vein of their arm or hand, this contrast highlights the brains blood vessels
for a more clearer and detailed image. Advantages of a CT scan it is non-invasive, useful for spotting
and identifying the precise location and extent of damage to or abnormalities in various brain
structures or areas. Disadvantages is that it only shows the brains structure or anatomy, it does not
provide information about the activity of the brain; brain function.
MRI
Magnetic resonance imaging is a neuroimaging technique that uses harmless magnetic fields and
radio waves to vibrate atoms in the brains neurons to produce an image of the brain. In this
procedure, vibrations are detected by a magnet in a chamber surrounding the person, and put
straight to a computer; computer then processes vibrations and assembles them into a coloured
image that shows the areas of low and high brain activity. MRI is used for diagnosing structural
abnormalities of the brain. Advantages of an MRI are that it has enabled even more precision in the
study of the structure of the live human brain in a non-invasive and harmless way in contrast to CT
Scans. Disadvantages are that it cannot be used on people with internal metallic devices, and that it
only shows brain structure and anatomy not function.
PET
Position emission tomography is a neuroimaging technique that uses a radioactive tracer to enable
production of a computer generated image that provides information about brain structure, activity
and function during various tasks. In the procedure patients are involved in a cognitive or
behavioural activity (thinking, imagining, remembering, talking or moving body parts) to records the
levels of activity in different areas of the brain. PET provides images of the ‘working brain’ by a
coloured ‘map’ of the brains activity; different colours indicate areas of greater or lower activity.
Advantages of a PET scan are that it enables detailed images of the functioning brain; ‘at work’.
Disadvantages are that researches cannot determine whether an active brain area is actually
involved in the mental processes or behaviour under investigation and that because radioactivity
decays rapidly, it is limited to studying relatively short tasks.
SPECT
Single photon emission computed tomography uses a longer lasting radioactive tracer (than an PET
scan) and a scanner to record data that a computer uses to construct a 2D or 3D image of active
brain regions. The SPECT procedure is exactly the same as a PET scan, except SPECT’s duration is
longer as a longer lasting radioactive tracer is used. Advantages of this procedure is that patients can
be given longer lasting tasks than PET, and that it is significantly less expensive than an PET scan. .
Disadvantages are that researches cannot determine whether an active brain area is actually
involved in the mental processes or behaviour under investigation.
fMRI
Functional magnetic resonance imaging is a neuroimaging technique that enables the identification
of brain areas that are particularly active during a given task by detecting changes in oxygen levels in
the blood flowing through the brain. This procedure is based on a standard MRI and measures blood
oxygen levels in the functioning brain; a computer analyses blood oxygen levels in the area and
creates an image with colour variations that reflect on the level of activity of different brain areas
and structures while patient engages in various tasks. Advantages if an fMRI are that it can take
numerous pictures of the brain in rapid succession and can detect brain changes as they occur, and
are more highly detailed and more precise than an PET or SPECT scan. Disadvantage of this
procedure is that there is no scope for suggesting relationships between active and inactive areas
and mental processes and behaviours under investigation.
By Liam Brooks