Chapter 19, End of Chapter, Review Questions, Exercise 1

Electroencephalogram (EEG) is a method to measure the brain's electrical activity. Synaptic excitation of the neuronal dendrites in the cerebral cortex generates current which is measured in terms of voltage by the EEG.

The generation of an EEG signal with a big amplitude making it easily measurable requires the activation of thousands of neurons as the signal has to move through many layers of non-neural tissues, such as meninges, fluids, bones of the skull, and skin to reach the electrode. The detection of the signal is small enough to be detected by the EEG.

The simultaneous excitation of the number of cells will result in the summation of tiny signals to generate one large surface signal.

The amplitude of the EEG signal is dependent on the synchronized activity of the underlying neurons. When a group of neurons are excited simultaneously such that the small signals produced are synchronized and summed to generate a large surface signal. A rather different case allows the reception of signals with the same amount of excitation by each  neuron, which is later spread out with the increased time period. This results in the occurrence of meager and irregular summed signals. The change in the time period of the activity performance affects the amplitude and the frequency of the signals produced during the measurement of EEG. 

The EEG with slow frequencies will result in synchronized activity of the neurons, leading to the generation of large amplitudes. However, EEG with fast frequencies will not result in synchronized activation of the underlying neurons, which will result in the generation of smaller amplitudes.