A variety of procedures are used by physiological psychologists to study the functions of different areas of the brain. Some of them are very old methods and outdated; some of them are most recent in origin and frequently used by modern investigators. The methods help us to study the localization of the functional areas of the brain.
Surgical Ablation or Method of Extirpation:
In lesioning or extirpation, tissues at a particular part of the brain are destroyed electrically and the behavioral effects of such destruction are observed. In surgical ablation, a part of the brain is surgically removed. Human beings cannot be studied with these methods directly excepting in situations when an accident or disease requires a lesion or when the removal of abnormal brain tissue is essential to the well being of human beings.
A specific part of the brain may be stimulated either by electric current or by chemicals. Through electrical stimulation, we can only stimulate the desired part of the brain. But by chemical methods, we can stimulate or defunct a particular part of the brain for a fixed period of time and observe their effects on behavior.
Electrical Recording or Action Potential Method:
The rhythmical electrical discharges of the brain are recorded by an instrument called electroencephalogram (EEG). The EEG can detect minute electrical activities of the brain cells during sleep, arousal and activity. The brain parts having greatest electrical activity can be linked with behaviors and sensations of the body. This will tell how the body surfaces are represented in the brain.
The structural features of neurons and fiber connections can be studied through microscopic examination of brain tissues. This method is called as histology. Three important techniques of histology have been developed. They are:
(a) fixation in which the tissue is preserved in a fixative such as formalin,
(b) sectioning in which the tissue is sliced through a microtone (an instrument), and
(c) staining in which the desired portion of the brain or cell is stained or dyed (colored) before its microscopic examination.
Scanning and Imaging Techniques:
The advances in modern technology have made it possible to study the internal workings of the brain without having to cut surgically into a person's skull. The brain scanning are the mechanical and electrical measurements of biochemical and electrical activities of specified brain areas. Some of these techniques are discussed below.
Computerized Axial Tomography (CAT:
Thousands of separate X-rays are taken at slightly different angles, and the computer constructs an image of the structures of the brain by combining these X-rays. It is very useful for showing abnormalities in the structure of the brain such as swelling and enlargement of certain parts. But it does not provide information about brain activity.
Magnetic Resonance Imaging (MRI):
It produces a strong magnetic field in which the person's head is positioned. The radio waves directed at the brain cause the hydrogen atoms to emit signals, which are analyzed by a computer. The details of the MRI are superior to CAT scan, because it can distinguish between closely related brain structures.
Positron Emission Tomography (PET):
It shows the biochemical activity within the brain at a given moment in time. The PET scan begins with the injection of radioactive water into the blood stream, which makes its way to the brain. The computer measures the location of radiation within the brain and determines which are the more active regions. The technique is good to provide a picture of brain's functioning.
Superconducting Quantum Interference Device (SQUID):
It is sensitive to tiny changes in magnetic fields that occur when neurons fire. When neurons fire, they create an electric current, which gives rise to a magnetic field. This magnetic field is interpreted by the SQUID as neural activity. This helps to pinpoint the location of neural activity.