Practice question

Electroencephalography records summed extracellular fields generated by thousands of aligned cortical pyramidal neurons. Action potentials are too brief, approximately one millisecond, and occur asynchronously, so their currents cancel at distant scalp electrodes. Sustained excitatory and inhibitory postsynaptic potentials lasting tens of milliseconds can summate temporally and spatially across cortical columns, creating dipoles detectable noninvasively. Thus raw EEG reflects integrated synaptic drive, not individual spikes, simple ion flux or radioisotope emission. This principle explains sensitivity to arousal, cognition and epileptic hypersynchrony linked to postsynaptic currents.