Relationship between action potentials and EEG recordings

Question

It is possible that I am overthinking this but I have difficulties relating the neural activation to the amplitude and frequency of EEG recordings. For example; if at the EEG location P3/P4 we observe alpha waves at 10Herts, what will that tell us about the action potentials and membrane polarisation within the population of neurons generating the wave at this frequency? Also, high amplitude within alpha frequency may indicate attention deficits, but how is the high amplitude related to or explained in terms of electrochemical activity within a neuron? Informed replies are very much appreciated! Many thanks

Answer 1

Most of the EEG waves are not directly generated by action potential, because it is too short and has a high frequency. They are generated by synaptic activity (overall propagation potential of axons).

The amplitude of this propagation potential depends on the impedance of the brain. Higher impedance means higher amplitude. Impedance is higher for low frequency signals.

The amplitude is also affected by the direction of the EEG vector so parallel axons which go in the same direction should produce a higher wave in amplitude.

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Reference: Rudell AP, Fox SE. The propagation potential. An axonal response with implications for scalp-recorded EEG. Biophys. J. 1991 Sep;60(3):556-67. doi: 10.1016/S0006-3495(91)82085-9. PubMed PMID: 1932547.