Much of our early knowledge of the human brain comes from clinical studies of individuals who suffered brain damage from injury or disease or who had brain surgery to relieve another condition. Modern discoveries have relied largely on technology that enables researchers to "look inside" the brain while it works:

• Brain lesioning. The study of naturally occurring brain lesions (abnormal disruption of the tissue of the brain) in humans has provided considerable information about how the brain functions. Neuroscientists also produce lesions in laboratory animals to determine the effects on the animals' behavior. These lesions may be made by surgically removing brain tissue, destroying tissue with a laser, or eliminating tissue by injecting it with a drug. Sometimes a drug is administered that only temporarily inactivates an area of the brain. The organism's behavior can be studied while the area is inactivated, and after the effects of the drug have worn off, brain activity in the area returns to normal.
• Staining. Much of the progress in charting neural networks, the complex pathways in the brain and nervous system through which information flows, has come about through the use of stains, or dyes, that are selectively absorbed by neurons. One commonly used stain is horseradish peroxidase. Using high-powered microscopes, neuroscientists can see which neurons absorb the stains and determine how they are connected.
• Electrical recording. Also widely used is the electroencephalograph (EEG),which records the electrical activity of the brain through electrodes placed on the scalp. This device has been used to assess brain damage, epilepsy, and other problems. Another option is single-unit recording, in which a thin probe is inserted in or near an individual neuron to provide information about that single neuron's electrical activity. The probe transmits the neuron's electrical activity to an amplifier so that researchers can "see" it.
• Brain imaging. For years X rays have been used to reveal damage inside or outside our bodies. But a single X ray of the brain is hard to interpret because it shows only a two-dimensional image. A newer technique called computerized tomography (CT scan) produces a three-dimensional image obtained from X rays of the head that are assembled into a composite image by a computer. The CT scan provides valuable information about the location and extent of damage due to a stroke, language disorder, or loss of memory. Positron-emission tomography (PET scan) measures the amount of glucose in various areas of the brain, then sends this information to a computer for analysis. Because glucose levels vary with the levels of brain activity, tracing the amounts of glucose generates a picture of brain functioning. Another technique, magnetic resonance imaging (MRI), involves creating a magnetic field around a person's body and using radio waves to construct images of the person's tissues and biochemical activities. MRI provides very clear pictures of the brain's interior, does not require injecting the brain with a substance, and, unlike X-rays, does not pose a problem of radiation overexposure (Petersen, 2001; Toga & Mazziota, 1999).

1		A neuroscientist who surgically removes a portion of the brain of a guinea pig is using the technique of _______________.
			A)	brain lesioning
			B)	staining
			C)	electrical recording
			D)	brain imaging
2		The brain imaging method that measures the amount of glucose in areas of the brain in order to assess brain functioning is called ____________________.
			A)	electroencephographology
			B)	computerized tomography
			C)	positron-emission tomography
			D)	magnetic resonance imaging
3		A three-dimensional image of the brain obtained by combining X rays is called
			A)	an electroencephalograph
			B)	a CT scan
			C)	positron-emission tomography
			D)	magnetic resonance imaging