Electrical Brain Activity

Electrical Brain Activity

Metabolism is always accompanied by electrical phenomena; The electrical activity of the brain can be recorded using a device called an electroencephalograph. To do this, electrodes are attached to different areas of the scalp using adhesive tape and the activity of the underlying parts of the cerebral cortex is examined. Electroencephalography has shown that the brain is constantly in a state of activity, even when we are not thinking about anything, and that the most regular expressions of activity - the so-called alpha waves - emanate from the visual areas of the occipital lobe when a person is at rest and eyes its closed.

These waves occur rhythmically with a frequency of 9-10 per sec and with an amplitude of about 45 mV. When the eyes are open, the alpha waves disappear and are replaced by faster, irregular waves. The latter are caused by visible objects; this can be shown by exposing the eyes to some periodic stimulus, for example, a light flashing at regular intervals: then waves with the same rhythm appear on the electroencephalogram.

Sleep is the only normal state in which the electrical activity of the brain is dramatically altered. During sleep, the waves become slower and higher (i.e., their potential increases) as the person falls into an increasingly deeper state of unconsciousness. Irregular waves are recorded during dreams. In some brain diseases, the nature of the waves changes. For example, epileptics have a unique and easily recognizable type of electroencephalogram; similar changes are found in people who have never had an epileptic seizure, but under certain conditions one could occur. The location of brain tumors can be determined by determining which part of the brain the pathological waves are coming from.