Cortical Evoked Potentials (CEP - VEP, ABR, SSEP):

All evoked responses should always be recorded by a qualified individual. This may either be an HPCSA registered Clinical Neurophysiologist or in some instances similar tests can be performed by an audiologist of ophthalmologist. 

It is important that you know whether the person performing these tests is registered with the HPCSA and received the necessary specialised training.

Somatosensory Evoked Potentials (SSEP) evaluate the long spinal tracts and cortical white matter connections in the brain. 

A SSEP is a test done by a neurophysiologist that record how fast your nerves transmit signals from your skin through your nerves and spine to your midbrain and sensory processing are in your brain. It measures how long it takes the signs to reach the processing area in your brain and in this way we can tell your doctor if there is any block in the nerve pathway between the stimulus and the brain. This is the only diagnostic alternative to imaging and the only objective functional evaluation of positive structural findings on imaging. 

• How is a SSEP done

During an SSEP 5 to 6 electrodes will be pasted to the scalp and a few over the back of your neck and lower back over your spine. Small electrical impulses will be given to a nerve at your wrist or ankle. You will experience a tingling sensation and your thumb, or toes may twitch in time with the stimulations. This is not dangerous and will not cause harm but may be uncomfortable for some patients.

Before the test, you’ll need to make sure your hair is clean and doesn’t have any hair sprays, oils or gels in it and your skin on your hands, feet, is clean and doesn’t have any creams, oils or lotions on it. 

These products can interfere with the function of the electrodes.

Visual evoked potentials

A visual evoked potential (VEP) test is a non-invasive test that helps to diagnose certain conditions that affect how your eyes and brain work together to interpret what you see.

A VEP test assesses the function of your visual pathway, which includes your eyes, optic or visual nerve, the optic chiasm in your brain where some of the optic nerve fibres coming from one eye cross optic nerve fibres from the other eye, the optic tract pathway between the optic chiasm and your brain, the optic radiation that transmits visual signals coming from your retina, optic nerve and optic tract and the area of the brain that receives and processes these signals.

• How is a VEP done

During a VEP the neurophysiologist will place about five electrodes on your head. You will be asked to look at a computer screen with a white and black block pattern or flashing light in a dark room with one eye at a time.

The neurophysiologist will then be able to record how long the signal your eye generates takes to transmit to your brain. 

Small electrodes may also be placed under the lower eyelid to record the potentials that your retina generates to transmit to your brain.

Before the test, you’ll need to make sure your hair is clean and doesn’t have any hair sprays, oils or gels in it.

These products can interfere with the function of the electrodes.

If you are prescribed glasses please bring these to the appointment. 

Auditory brainstem evoked responses

Auditory brainstem responses are also referred to as and ABR or Brainstem Auditory Evoked Potentials (BAEP) or Brainstem Auditory Evoked Responses (BAER).

This test records the small impulses sent between your ear and your brain and can detect if there is any disruption along the nerve or midbrain pathways. 

• How is a ABR done

During a ABR test the neurophysiologist will place 4 or 5 electrodes on your head and around your ear. Your ear will be stimulated by placing special earphone over your ears or even very small earphones in your outer ear canal. Rapid clicking sounds, or short pips of special frequency sounds, will be played at one ear at a time while the neurophysiologist records your auditory nerve responses on a computer. These responses will be displayed as traces on a computer screen that can be analysed to calculate how long the signal your ear generates takes to transmit to your brain.

Before the test, you’ll need to make sure your hair is clean and doesn’t have any hair sprays, oils or gels in it.

These products can interfere with the function of the electrodes.

• Some reasons why your doctor may refer you for evoked responses

In absence of positive imaging findings CEPs are the only objective non-invasive, investigative alternative for diagnosis and localisation of long spinal tract and white matter lesion diseases such as MS.

Pre- and postsurgical evaluation and monitoring of recovery of nerve and muscle injuries or reversible or treatable chronic diseases.

Differentiation between peripheral, spinal or central nervous system functional pathology of either white or grey matter that may not be visible on imaging or clearly definable by subjective clinical examination.