Techniques for Studying the Nervous System

Modified: 2024-06-02 10:49 PM CDST

• 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.
• Somedramatic data have come from animal research using this method.
• 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.