Evoked potential and sense threshold examinations

SEP studies the functionality of the sensory pathways of the nervous system. The stimulus can be a small electrical shock to the wrist and ankle, for example. Electrodes attached to the skin are used to measure the progress of nerve impulses along the nerves and neural pathways from the stimulus site to the cerebral cortex.

Patient instructions for a somatosensory evoked potentials examination (Hoito-ohjeet.fi)

VEP provides information on the functionality of the visual pathways. The stimulus can be a flashing light or a changing checkerboard pattern, for example. The changes in the electrical activity of the brain caused by the visual stimulus are measured with electrodes attached to the scalp.

Patient instructions for a visual evoked potential examination (Hoito-ohjeet.fi)

Electrophysiological testing of the retina or ERG examines the electrical activity in the retina of the eye. A photic stimulus causes responses in the receptor cells of the retina. These are measured using sensors that resemble contact lenses. For the examination, the conjunctiva are numbed and the pupils dilated with eye drops. The examination takes place is in a nearly dark room.

Patient instructions for an electroretinography (Hoito-ohjeet.fi)

BAEP studies the activity of the neural pathways between the ear and the brainstem. The examination measures responses to audio stimuli delivered through headphones using measurement electrodes on the headphones and the scalp.

Patient instructions for a brainstem auditory evoked potential examination (Hoito-ohjeet.fi)

MEP studies the functionality of motor pathways. Magnetic pulses are used to activate the cerebral cortex from outside the skull and nerve roots in the neck and lumbar region. The stimulus causes muscle contractions in the hands and feet, which are measured by electrodes attached to the skin. The device can also be used to study cortical responses to cold stimuli.

Patient instructions for a motor evoked potential examination (Hoito-ohjeet.fi)

CHEP studies the pathways that relay information on temperature sensations. A hot stimulus is applied to the skin and the response in the brain is recorded with measuring electrodes attached to the scalp.

Patient instructions for a contact heat evoked potential examination (Hoito-ohjeet.fi)

QST is used to determine the cold, heat, cold pain and heat pain thresholds of the skin. These skin sensations are transmitted to the central nervous system by thin sensory nerve fibres. The examination is used not only for the detection of peripheral small fibre neuropathy and local peripheral nerve damage, but also to study central nervous system disorders affecting the sensory pathways for heat.

The measurements involve the entire small fiber nerve system from the skin to the cerebral cortex. In the examination a small plate is placed on the skin, which is then cooled or heated. At the touch of a button, the patient indicates when the skin sensation changes from neutral to cold or hot, as well as the sensation of pain experienced due to the cold or heat.

Patient instructions for quantitative sensory testing (Hoito-ohjeet.fi)

A vibration sense threshold examination is used to study the functionality of thick sensory nerve fibres. It involves placing a vibrating probe on the patient’s skin. As the intensity of the vibration is increased, the patient reports the first time they detect the vibration. This intensity is recorded as the vibration sense threshold.

Patient instructions for a vibration sense threshold examination (Hoito-ohjeet.fi)