Lesion methods are
invasive, and involve cutting or severing a part of the brain.
Ablation methods are similar, except they involve the destruction of
a part of the brain.
After the lesion or ablation is made, the animal
(humans are never used in experiments of this kind) is observed to
determine the effects of the lesion or ablation.
These methods are
relatively crude and are not used as much as previously.
Lesions and ablations can be studied in humans after the fact.
For
example, following World War I, large numbers of men who had been
shot in the head and lived were available for study.
Auto and
motorcycle accident victims can be studied in the same way, but not experimentally.
Stimulation methods are used extensively.
In electrical
stimulation, tiny electrodes are implanted in the brain.
There, they
can deliver a very mild electric current that activates that area of
the brain.
The electrodes are permanently implanted, and do not seem
to interfere with the animal's routine activities.
Some human work
has been done with this method, but it is usually done in an attempt
to relieve a medical condition, not as experimentation.
Somedramatic
data have come from animal research using this method.
For example,
Delgado implanted an electrode in the brain of a bull.
Then the bull
was induced to charge, and in mid-charge a current was delivered to a
part of the bull's brain. (The command was sent by radio telemetry,
so there were no wires.
Look carefully and you will see the device's antenna in Delgado's left hand.) The bull came to a screeching halt, and
begin to paw the ground.
Other research in this area has demonstrated
that applying a current to the appropriate area in a rat's brain
causes the rat to become immediately aggressive.
When the current
stops, the aggression stops.
Also, the discovery of the so-called
pleasure centers of the brain was accomplished using this method.
Olds and Milner found they could cause rats to press a bar to deliver
electrical stimulation to their brains.
When the electrodes were
implanted in the proper place in the brain, rats would continue to
stimulate themselves for hours.
Similar pleasure centers have been
found in humans.
Patients report the sensation as very similar to
profound sexual arousal.
As mentioned above, human work using electrical stimulation is
usually clinical, or done for some therapeutic reason.
The author of Jurassic Park, Michael Crichton, earlier wrote a novel called
Terminal Man.
That earlier novel was about the use of electrical stimulation
on humans.
One of the characters in that novel is a drugged-out hippy
type who kidnaps the MD doing the research and attempts to persuade
the doctor to rig him up so that he can stimulate himself at will.
The hippy character believes that electrical stimulation will be the
ultimate drug.
Popular fiction like Star Trek has also described
methods similar to electrical stimulation.
For example, in one
episode, Kirk and others are forced to wear rings around their necks
that apparently stimulate brain pain areas when they do not obey.
So,
there could be real reason for concern over the use of stimulation
methods for rewarding and punishing human subjects, as has already
been voiced in science-fiction accounts.
Chemical stimulation is very similar to electrical stimulation,
except that instead of an electrode, a small tube, a cannula, is
inserted into the brain.
Then, chemicals, usually crystalline forms
of neurotransmitter, are introduced into the tube to stimulate the
brain at the point at the end of the cannula.
Recording techniques measure the activity of neurons.
Single-cell
recording measures the output of just one neuron. In single-cell
recording, a small recording electrode is inserted into the axon of a
neuron. Then, that electrode transmits that cell's activity. The
activity consists of a series of discrete, similar pulses. This
discrete activity will prove important later when I discuss neural
integration. Hubel and Wiesel's Nobel Prize winning research demonstrates single-cell recording.
The EEG, or electroencephalogram, records from multiple
points on the scalp simultaneously. The EEG is recording the activity
of billions of neurons simultaneously. The output of the EEG is a
complex curve. Research using this technique has proven especially
helpful in studying sleep and wakefulness. This VIDEO explains much about the EEG.
Biochemical techniques are used to map out the various
neurotransmitter systems in the nervous system.
Depression, for
example, can be linked to levels of neurotransmitter, and drug
therapy for depression alters those levels.
Imaging techniques are a newer and exciting way of studying the
brain.
Years ago surgeons had to perform exploratory surgeries in order to diagnose brain problems.
Today, many such problems can be diagnosed non surgically.
(BTW, in 1996 I had a meningioma, a type of brain tumor, removed from the right side of my brain.
An MRI beforehand pinpointed its location for the surgeon. I will discuss the effects and symptoms of that brain surgery elsewhere in this section.)
All imaging techniques use some form of energy and modern
computers to create detailed pictures of the brain.
These imaging
techniques include
magnetic resonance imaging (MRI) which uses
magnetism
computer-assisted tomography (CAT scan) which uses X-rays
positron emission tomography (PET scan) which uses the brain's
metabolic activity.