Bodily Defenses Image Map

Learning What The Whole Brain Does

Brain Waves - Known as EEG (electroencephalogram)

The brain generates electrical currents. Some of these currents in the part of the brain that is nearest to the scalp are large enough to be detected with electrodes placed on the scalp. This electrical activity is small (on the order of 20 to 100 millionths of a volt). The activity detected by any one electrode is a summation of the voltage fields created by millions of neurons nearest to the electrode.

By placing electrodes in an orderly way, it is possible to know what areas of the cortex are being monitored by any given electrode. Pictured here is the standardized electrode placement system used in clinical medicine.

A useful Web site that explains the EEG and how it changes in different diseases is found by clicking here.  


The EEG can be used to create a mapped image of the electrical activity over the surface of the brain. Other kinds of images allow scientists to see what is going on deep inside the brain, where the voltages are too small to be detected by electrodes at the surface.

These other techniques indirectly measure either blood flow or oxygen consumption at various brain areas. 

Example brain image, using the so-called PET scan method. The more active an area is, the more oxygen it consumes and the more blood flow it gets. These more active areas show as bright red or orange colors in image maps.

A newer imaging technique is called MRI (magnetic resonance imaging), which is easier to perform and provides similar information about blood flow and oxygen consumption.

Imaging allows us to test such questions as: "Can you walk and chew gum at the same time?" Well of course you can, but the point is would you do things better if you did them one at a time. In one study, people were imaged while they performed two mental tasks, either separately or at the same time. The amount of brain activity devoted to each task was greater when the tasks were performed separately than when done at the same time. Common experience teaches this too. If you really want to "get into" a music recording, you close your eyes, right?

Imaging equipment can be tuned to detect metabolic activity or volume of cells. Recent studies of brain volume shows a marked maturation process in children in which cells die at a rate of about 1% per year. Click here to see images. This is a normal process of "pruning" away nerve cells that are not useful. In children who develop schizophrenia, the death rate is much faster and they don't have enough neurons left to function normally. Click here for a short video on images in schizophrenia.

Click here for a complete middle-school level overview of all the methods used to learn about the nervous system.

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