Merck Manual

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Measurement of Evoked Responses

(Evoked Potentials)

By

Mark Freedman

, MD, MSc, University of Ottawa

Reviewed/Revised Aug 2023
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Visual, auditory, or tactile stimuli are used to activate corresponding areas of the cerebral cortex, resulting in focal cortical electrical activity. Ordinarily, these small potentials are lost in electroencephalography (EEG) background noise, but computer processing cancels out the noise to reveal a waveform. Latency, duration, and amplitude of the evoked responses indicate whether the tested sensory pathway is intact.

Evoked responses are particularly useful for the following:

When integrity of the brain stem is in question, brain stem auditory evoked responses is an objective test.

Somatosensory evoked responses may pinpoint the physiologic disturbance when a structural disorder (eg, metastatic carcinoma that invades the plexus and spinal cord) affects multiple levels of the neuraxis.

Somatosensory evoked responses can also help predict the prognosis of patients in a coma, particularly those with hypothermia, when the usual bedside indicators are unclear.

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NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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