Describe how each method of testing, measuring, or observing helps to measure the brain’s functioning.

Ablation and Stimulation

Beyond the accidental discovery of the effects of damage to the brain (like my football injury), science has attempted to analyze and study the brain through various other methods. One method is clinical observations of people like me, which can show us where someone has damaged his or her nervous system. Next, we observe the changes the patient demonstrates or reports. (Caution: do not cause brain damage to yourself or others to test this method.) When many or all of the people who have received damage to a specific part of the brain report the same experiences, we conclude that that part of the brain influences that experience. Phineas Gage was the victim of accidental damage to his brain. His story and skull have provided much insight into the brain. He was a railroad construction foreman in the mid-1800s. A tamping rod was accidentally blasted through his head and skull (from under his left cheek through the top of his skull) and damaged both frontal lobes. Miraculously, he lived and suffered very few major intellectual or physical handicaps. He did, however, suffer some emotional and personality changes or handicaps. Once a dependable and personable person and worker, he was never the same again.

In the ablation method, a portion of the brain is intentionally removed and then behavioral changes are observed. This method results in permanent changes and, understandably, there have rarely been any volunteers. Animals have usually been used in this method, but brain surgery for tumors or other needed surgical interventions have led to some intentional and incidental observations using ablation.

Direct stimulation is another way to influence and observe brain activity. This is usually done with mild electric stimulation. One advantage to this form of observation and study is that no damage is caused to anyone. Another benefit is that any part of the brain can be stimulated. The biggest disadvantage is that it is a very expensive and involved process.

Monitors & Scans: EEG, PET, CT (CAT), and MRI

Recording the brain’s activity without invading the skull continues to dominate the current preferences of measuring and recording brain activity. An electroencephalograph is an instrument that measures the brain’s activity by printing waves of activity in the form of an electroencephalogram (EEG). The EEG is a measure of the amount of metabolic brain activity. If the brain is inactive, the EEG shows a flat line. When thinking is active, the EEG shows a jagged line with highs and lows.

Another measure of metabolic mental activity is the PET (positron emission tomography) scan. Subjects are injected with low doses of radioactive sugar (glucose), which can be scanned to observe and measure the parts of the brain with the highest metabolic activity during specific thinking activities. The PET is preferred to the EEG because it does not just measure amount of brain activity, but it also measures where that activity is occurring.

The CAT or CT (computed tomography) scan also detects location, but not of mental activity. The CAT scan x-rays the brain to detect the location of brain abnormalities, lesions, or damage. This kind of scan is compiled by making a composite of individual x-ray pictures taken from many different perspectives.

An MRI (magnetic resonance imaging) scans over the top of the brain with magnetic and radio waves to create a detailed picture of the density or concentration of tissue in the brain—it’s kind of a topographical map of the brain. Tumors, water on the brain, contusions, brain tissue damage, or other structural abnormalities can be seen with this scan. MRI scans have proven to be the best scan to detect schizophrenia.