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Measurement of Evoked Responses (Potentials)

By

Michael C. Levin

, MD, College of Medicine, University of Saskatchewan

Last full review/revision Jul 2021| Content last modified Jul 2021
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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 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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