VEMP (Vestibuler Evoked Myogenik Potentials )
The VEMP investigates otolith and vestibular nerve function. Dysfunction is characterized by feeling similar to being on a boat or an elevator. It may be a spinning sensation when people say that they are dizzy.
The VEMP is a short-latency electromyographic (EMG) potential and it is evoked in response to high-level acoustic stimuli. The responses are mediated by the vestibular system. It provides ear-specific information about otolith and nerve functions
The Vestibulo-Ocular System ( VOR)
To continue with this basic review, think about the system. We receive an input, the brain processes it, and then we get the output. In this case of balance, we have ears, vision and somatosensory systems that are taking in information. When the brain receives information, it has to process who or what it needs to respond. It sends that message out to the reflex. This is the process that keeps us balanced, upright, and able to walk and multitask.
The saccule is responsible for acceleration in the vertical plane. When the saccule is intact, you are comfortable going up and down in an elevator. The utricle is responsible for acceleration in the horizontal plane, such as driving in a car. Once the otolith senses the motion, the brain sends the message to the reflex. The vestibulo-ocular reflex (VOR) is going to maintain visual acuity. The vestibule-spinal reflex (VSR) maintains posture and gait. The vestibulo-colic reflex (VCR) maintains head stability. When the brain receives all this information, it is able to determine what piece the body needs to keep it upright.
What are the Differences Between cVEMP and oVEMP?
We have to understand the difference between the cervical VEMP (cVEMP) and the ocular VEMP (oVEMP). The cVEMP tests saccule and inferior nerve. It is recorded from the sternocleidomastoid muscle (SCM). It is an inhibitory potential and an ipsilateral response. When a muscle is flexed, there is a split second within that flex where it releases. That provides the waveform or the response from the sound.
The oVEMP is primarily a utricle and superior nerve response. A little part of this oVEMP response comes from the saccule. This is an excitatory response that we record from the extraocular muscles. What generates that waveform is the person looking up; this a contralateral response. When we stimulate the right, we record the left and vice versa.