Electro-encephalograph (EEG)
In 1929, Hens Berger is credited to have found some electrical activity when he connect a galvanometer to human scalp. It gave birth to electro-encephalography. EEG is an electrically operated instrument having array of 16-30 electrode, which when attached to the scalp for short time gives electric wave signals. It operates by detecting the brain's electrical charge which is maintained by billions of neurons. The Neurons are electrically charged due to continuous pumping of ions by membrane transport proteins across their membrane. Neurons constantly exchange ions with the extracellular fluid, e.g. to maintain resting membrane potential. When many ions having similar charge are pushed out of several neurons at the same time, they can push their neighbours, who further apply force to their neighbours, and so on such that a wave forms. When the wave of ions reaches the electrodes attached to the scalp, they can give or take electrons on or from the metal of the electrodes. Since metal can conducts these electrons easily, voltages difference between any two electrodes can be measured by a voltmeter. Recording these voltages for a specific time gives us the EEG. A schematic of typical EEG frequency display system is shown in Figure 14.3.

 

Fig. 14.3: EEG frequency display system