Modified: 2020-06-08
There are many ways to study the nervous system.
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. Some dramatic 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 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. Fifty 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 throughout this section.)
All imaging techniques use some form of energy and modern computers to create detailed pictures of the brain.