Evoked Potentials Explained: VEP, BAER and SSEP

Evoked potentials (EPs) measure how quickly and reliably a sensory signal travels from the periphery to the brain. They are objective and non-invasive, and they can be recorded on a standard EMG/EP system.

How EPs work

A stimulus (light, sound or electrical) is repeated many times. The system averages the brain’s responses, which cancels random background EEG and leaves a consistent waveform with recognisable peaks. Clinicians measure peak latencies and amplitudes.

Visual evoked potential (VEP)

• Stimulus: a pattern-reversal checkerboard or LED goggles (flash VEP).
• Key peak: P100.
• Uses: optic neuritis, multiple sclerosis, compressive optic lesions, and assessing patients who cannot communicate.

Brainstem auditory evoked response (BAER/AEP)

• Stimulus: clicks through headphones.
• Key peaks: waves I–V, reflecting the auditory nerve and brainstem.
• Uses: infant hearing screening, acoustic neuroma screening, brainstem lesions and intraoperative monitoring.

Somatosensory evoked potential (SSEP)

• Stimulus: electrical stimulation of the median or tibial nerve.
• Recording: peripheral, spinal and cortical sites.
• Uses: spinal cord lesions, demyelination, coma prognosis and intraoperative monitoring.

Cognitive potentials

P300 and late responses are used in cognitive assessment and research.

Equipment needed

• An EMG/EP system with averaging software such as the NEUROSTIM range.
• LED goggles or a pattern monitor for VEP.
• Headphones for BAER.
• A peripheral stimulator for SSEP.
• More channels (4 or more) make SSEP easier. See 2 vs 4 channel EMG.

Tips for good recordings

• Relaxed, comfortable patient.
• Low electrode impedance.
• Correct stimulus parameters and enough averages.
• Replicate each trial to confirm the waveform.

RS Enterprises supplies complete EMG/EP systems with application training. Request a demo.