Early research with the EEG resulted in understanding the nature of CNS arousal mediated by the reticular activating system. Later studies identified drug effects on the CNS and the EEG has been used as an aid to understanding human cognition. Recently a number of studies have examined the EEG changes associated with odors. EEG waves EEG waves reflect the mean excitation of pools of neurons. Excitatory inputs at synapses generate electric currents that flow in closed loops within the recipient neuron towards its axon, across the cell membrane into the extracellular space and, in that space, back to the synapse.
Inhibitory inputs generate loops moving in the opposite direction.
The cell body summates all the inputs and, if the threshold is reached, fires an action potential. Electrodes placed on the scalp record these currents after they leave the cell. The resulting EEGs indicate the excitation of whole groups of cells, not individuals, because the extracellular avenues from which the EEGs arise carry currents contributed by thousands of cells. Why EEG waves oscillate Alternating rises and falls in amplitude stem from negative-feedback circuits that are established by the interaction of pools of excitatory and inhibitory neurons. When the pools have been sensitized to input, even a small input can trigger a burst of high-amplitude oscillation.