Evoked potentials (EP) or evoked responses are electrical potentials recorded from a specific part of the nervous system, particularly the brain, in humans or animals – elicited by presentation of a stimulus or multiple stimuli.
A stimulus can be a light flash, sound, vibration, smell, pattern, or a change in the stimulating signal.
Different types of potentials result from stimuli of different modalities and types.
EPs are very faint signals. Their amplitudes range from nanovolts (nV) to several microvolts (μV, uV) which is thousands of times smaller than the tens of microvolts for EEG, millivolts (mV) for EMG, and often close to 20 millivolts for ECG.
Special equipment and signal-processing techniques – highly sensitive differential physiological amplifiers and digital signal averaging – are employed to record and extract EPs from the background noise of ongoing electrical brain activity (EEG), heart (ECG), muscular (EMG), ocular (nystagmus), and other biological signals, as well as from background electromagnetic interferences (EMI).
EP signals are recorded from cerebral cortex, brain stem, spinal cord, and peripheral nerves and sensory organs such as visual, auditory, and olfactory.
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