Physiologic basis of the EEG signal

This chapter is aimed at explaining the physiologic principles of EEG generation. It starts with basic notions on the flux of iones through the cell membrane to explain the concepts of depolarization, repolarization and action potential. Excitatory and inhibitory postsynaptic potentials, representing the most significant source of scalp-recorded EEG signals by creating a dipole through the vertically oriented pyramidal neurons are then described. The possible contribution of nonsynaptic intercellular events to the EEG signal is also reported. The relationship between the location of the synaptic activity within the cortex and the polarity of the surface potentials is explained. Factors influencing the characteristics of scalp-recorded EEG waves are summarized. Brain structures involved in the genesis of EEG rhythms and main circuits responsible for the occurrence and modulation of rhythmic behavior are illustrated.