Both surgical procedures and those involving measurement have been used to understand the way the brain functions.
Bisecting the brain. The brain may be bisected—that is, split into two hemispheres by severing the corpus callosum—for medical reasons (such as to treat epilepsy, or to remove tumors). After such a procedure, it is possible to compare the functioning of the left and right hemispheres (that is, to study cerebral laterality). For example, studies have been conducted showing the relationship of the hemisphere used and handedness (left or right) and hemisphere used and gender (whether males or females use one hemisphere or the other more). Cerebral laterality studies are conducted also in the absence of brain bisection by using special types of laboratory equipment that can block sensory input to one hemisphere.
Lesioning. Lesioning, the destruction of a portion of the brain (through strokes, accidents, or surgical procedures), helps identify the function associated with that portion of the brain.
Electrical stimulation of the brain. Electrodes can be implanted to very precise positions in the brain. Administration of small amounts of electric current into a brain structure helps identify its function.
Brain imaging procedures. Several brain imaging procedures have been used medically in recent years to identify problem areas in the brain.
The CT (computerized tomography) is a computer‐enhanced x‐ray of the brain.
PET scans (positron emission tomography) are used to map brain activity.
MRI (magnetic resonance imaging) makes use of radio waves, magnetic fields, and enhancement by computers to show three‐dimensional pictures.
Monitoring brain activity. Brain activity can be monitored by inserting electrodes into single neurons and recording single cell activity in laboratory studies. Activity of the entire brain can be measured through electroencephalography, a technique that records from electrodes placed on the scalp and produces a pattern of brain waves called an electroencephalogram. The procedure is used in both research and medicine. Upon examination of the frequency and amplitude of the brain waves, it is possible for an expert to differentiate between sleep and waking activity as well as to detect certain pathological conditions such as an epileptic seizure or a brain tumor.