The vestibulo-collic reflex

Until now there has no been no simple, reliable clinical test that assesses the function of the otolith organs. However, recent work has suggested the occurrence of an easily identifiable electromyographic (EMG) waveform in isometrically contracting sternomastoid muscles in response to loud clicks. This is thought to represent an otolith evoked disynaptic reflex. Equipment routinely used for evoked response audiometry (ERA) has been adapted to investigate this response. A short latency (8 ms) positive-negative EMG waveform has been recorded in 31 of 32 normal subjects. The latency of the positive peak (P1) is 11.7 ms (SD = 0.89), and the negative peak (N1) is 30.5 ms (SD = 1.89). It is predominantly ipsilateral, although a contralateral response was present in 35.5%. The response has also been recorded in three patients with a severe unilateral sensorineural hearing loss and normal caloric responses, and in a patient undergoing cochlear implantation for profound bilateral sensorineural hearing loss. Further work is required to delineate the value of this technique in investigating vestibular lesions.