Neurophysiological Basis of EEG

The Electro Encephalo Gram (EEG) records the bioelectric currents within the brain from the scalp. Pyramidal neurons dendrites organization in the cortex, running parallel with each other and perpendicular to the cortical surface, generate large extracellular currents recordable from the scalp as EEG. However, considering EEG just a tool to measure the result of cerebral cortical electrical activity is highly reductive. Although subcortical structures produce potentials that are not directly detectable on the scalp - since the electric field decreases in strength as the square of the distance from its source - these can be indirectly recorded by the EEG: EEG rhythms depend indeed on the synchronization of the waves deriving from the summation of synaptic potentials generated by the activity of the thalamocortical neurons. In the first part of this chapter, anatomo-physiological features of the cerebral cortex will be described with particular reference to the genesis of the electrical potentials. The second part will be more speficially dedicated to the genesis of the EEG potential and, finally, to a special focus on the specific EEG rhythms origin.