The brain have always fascinated humans, and particularly a German scientist
named Hans Berger, who discover electroencephalography (EEG) about 80 years
ago. After this, new methods for exploring it have been found and we can categorize
them into two main groups. Invasive and non-invasive. An invasive approach
requires physical implants of electrodes in humans or animals, making it possible
to measure single neurons or very local field potentials. A non-invasive approach
makes use of, for instance, magnetic resonance imaging (MRI) and EEG technology
to make measurements. Both gives different perspectives and enables us to
look inside the brain and to observe what happens (Kropotov, 2009). In EEG,
brain-related electrical potentials are recorded from the scalp. Pairs of conductive
electrodes (see figure 4.2) made of silver, for example, are used to read this electricity.
The difference in voltage between the electrodes are measured, and since
the signal is weak (30-100V) it has to be amplified. Current occurs when neurons
communicate. The simplest event is called action potential, and is a discharge
caused by fast opening and closing of Na+ and K+ ion channels in the neuron
membrane. If the membrane depolarize to some threshold, the neuron will ”fire”.
Tracking these discharges over time reveals the brain activity.