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Methods Used to Study the Brain

The brain's functions can be studied in many ways: effects of brain damage, effects of electrical, chemical (and recently magnetic) stimulation of the brain, measurement of electrical and chemical activity of the brain, and computer-based brain scans, which show structure or function of the brain through the intact skull.

Figure 2-2a. Location of the main brain areas where damage produces disturbed judgment and planning, impulsiveness, etc (front) or disturbed visual functioning (back).

  • Effects of brain damage. Damage to different brain areas produces different behavioral and psychological effects. For example, damage in the front end of the brain disturbs the ability to make decisions and to inhibit socially inappropriate behaviors. In contrast, damage to the back of the brain disturbs vision. Figure 2-2a illustrates the location of these two areas.

  • Effects of electrical and chemical stimulation.

    Figure 3-2a. EEG pattern in waking (top) and in deep sleep. The EEGs show about 2 seconds of activity (horizontal axis).

  • Recording electrical activity from the brain.
    • Recordings from the scalp. In 1929 Hans Berger discovered that electrical signals from the brain can be picked up through the scalp from silver disk electrodes pasted to it. These signals are called EEGs (which stands for electroencephalograms) or, informally, "brain waves." Figure 3-2a shows the EEGs for wakefulness (top) and deep sleep (middle and bottom). For a description of the EEG and its use to map how the brain works, click HERE.
    • Recordings from the brain. Very thin wire or glass tube electrodes, so thin they produce virtually no damage, can be put inside the brain itself(usually in experimental animals). Electrical signals from the brain show different patterns of activity associated with different mental processes. Figure 4-2a shows the response of a single nerve cell in the olfactory (smell) system to two different odors. When nerve cells are excited they show more of the impulses each second. When they are inhibited the show fewer or none,

      Figure 4-2a. Response of a single nerve cell in the olfactory (smell) system to two odors. In record A, the nerve cell responds with a large increase in the rate (number/second) of impulses to Stim 1 but does not change in response to Stim 2. In record B, the neuron does not change its rate of impulses in response to Stim 1 but stops all impulses in response to Stim 2.

    • Chemical measurements of brain activity. In the past 20 years, several methods have been developed to measure chemical concentration and changes in concentration in small bits of the brains of awake, normally behaving rats and other animal species.
    • Computer-based brain scans. Starting about 1970, several computer-based devises were introduced that show the structure and function of the brain non-invasively (the scalp and skull are not opened). They provide picture of the brain as a series of slices, like the ones in Figures 3-2a and 4- 2a. Because they involve minimal invasion into the body, brain scans allow the study of brain structure and function in normal healthy volunteers, as well as people with diseases of the brain (or other parts of the body).
      • Devices that show brain structures. The CT (or CAT) scan is a rotating X-ray machine hooked up to a computer programmed to reconstruct slices through the brain from the x-ray measurements. The MRI uses changes in an intense magnetic field. It shows more detail than does the CT scan. They show the anatomy of the brain, allowing identification of brain damage and measurement of the size of different parts of the brain. For example, many people suffering from more severa cases of schizophrenia show smaller than normal-sized areas, especially in the front of the brain.
      • Devices that show brain function PET and fMRI scans measure the changing activity of each part of the brain. PET detects rapidly decaying radioactive atoms that are injected into the veins. fMRI uses changes in an intense magnetic field. Both methods measure changes in blood flow throughout the brain to show how active each small area of the brain is. The works because blood flow changes very rapidly in an area as it increases or decreases its activity. Such scans have shown that many people suffering from schizophrenia have abnormally low activity in the very front of the brain and may have abnormally high activity in a specific place on the side of the brain.

    Figure 3-2a. Right: CT scan showing a horizontal slice through the brain. Left: Approximate position of the slice.

    . Figure 3-2a shows shows a CAT scan as a horizontal slice through the brain. (The top of the slice is the front of the brain.) Figure 4-2a shows a PET scan comparing the brains of a normal person and a person suffering from obsessive-compulsive disorder. To go to an explanation of how PET works, click HERE. To go to an explanation of how MRI (also called NMR) works, click HERE. (Some background in physics is very helpful.)

    Figure 4-2a. Brain activity in a normal person and in a person suffering from obsessive-compulsive disorder