<Tr> <Td_colspan="2"> Epileptic spike and wave discharges monitored with EEG </Td> </Tr> <Tr> <Td_colspan="2"> (edit on Wikidata) </Td> </Tr> <P> Electroencephalography (EEG) is an electrophysiological monitoring method to record electrical activity of the brain . It is typically noninvasive, with the electrodes placed along the scalp, although invasive electrodes are sometimes used such as in electrocorticography . EEG measures voltage fluctuations resulting from ionic current within the neurons of the brain . In clinical contexts, EEG refers to the recording of the brain's spontaneous electrical activity over a period of time, as recorded from multiple electrodes placed on the scalp . Diagnostic applications generally focus either on event - related potentials or on the spectral content of EEG . The former investigates potential fluctuations time locked to an event like stimulus onset or button press . The latter analyses the type of neural oscillations (popularly called "brain waves") that can be observed in EEG signals in the frequency domain . </P> <P> EEG is most often used to diagnose epilepsy, which causes abnormalities in EEG readings . It is also used to diagnose sleep disorders, depth of anesthesia, coma, encephalopathies, and brain death . EEG used to be a first - line method of diagnosis for tumors, stroke and other focal brain disorders, but this use has decreased with the advent of high - resolution anatomical imaging techniques such as magnetic resonance imaging (MRI) and computed tomography (CT). Despite limited spatial resolution, EEG continues to be a valuable tool for research and diagnosis . It is one of the few mobile techniques available and offers millisecond - range temporal resolution which is not possible with CT, PET or MRI . </P>

Which technique measures the electrical activity of brain cells directly