Splenius capitis is a reliable target for measuring cervical vestibular evoked myogenic potentials in adults

Abstract

The cervical vestibular evoked myogenic potential (cVEMP) is a common and simple test of vestibulospinal reflex patency. In the clinic, cVEMPs are measured in response to loud sounds from the sternocleidomastoid (SCM) on the ventral neck, as subjects maintain an uncomfortable head posture needed to recruit SCM. Here we characterize the cVEMP in a dorsal neck turner (splenius capitis; SPL), and compare it with the SCM cVEMP. cVEMPs were recorded simultaneously via surface electromyography from SCM and SPL from 17 healthy subjects in a variety of postures, including head-turned postures adopted while either seated or standing, and the clinical posture. Like the SCM cVEMP recorded ipsilateral to the side of sound stimulation, the cVEMP on the contralateral SPL (synergistic with ipsilateral SCM) was characterized by a biphasic wave of muscle activity that began at ~ 13 ms. cVEMP reliability was higher on SPL vs. SCM in standing postures (chi-squared; P < 0.05), and equivalent results were obtained from SPL in a standing or seated posture. In 9 of the 17 subjects, we also obtained bilateral intramuscular (IM) recordings from SPL at the same time as the surface recordings. In these subjects, the initial surface response in SPL was associated with a consistent decrease in multi-unit IM SPL activity. Overall, these results demonstrate that SPL recordings offer a complimentary target for cVEMP assessments. The expression of SPL cVEMPs in simple head-turned postures may also improve the utility of cVEMP testing for vestibular assessment in children, the elderly, or non-compliant.

Animal Models of Vestibular Evoked Myogenic Potentials: The Past, Present, and Future

“…As in cats and monkeys, human SCM also has a higher proportion of fast fibers and a more advantageous moment arm ( 104 – 106 ), leading us to predict that recruitment of this muscle related to vestibular reflexes would also be reserved for tasks requiring larger amounts of muscle force or particularly extreme postures. This line of thinking, as well related concerns about getting SCM to a sufficient level of contraction in a variety of postures, led us to investigate in humans whether cVEMPs could be recorded on one or both of ipsilateral-SCM and contralateral-SPL, relative to the side of the stimulated ear, in a head-turned posture ( 107 ) (Figure 6A ). This muscle pair acts synergistically for head turns and postures away from the side of the stimulated ear.…”

“…Same format as Figure 1B . All parts of this figure take from data presented in Camp et al ( 107 ), with permission from Wiley and Sons.…”

The Contributions of Vestibular Evoked Myogenic Potentials and Acoustic Vestibular Stimulation to Our Understanding of the Vestibular System

“…This inconsistency may be due to the fact that SC is located amongst other muscles with differing actions and vestibular projections. In contrast, Camp et al ( 41 ) and Rosengren et al ( 42 ) recorded motor unit responses from within the SC muscle and found short-latency inhibitory responses at 12–14 ms on the contralateral side. Thus stimulation of one ear with AC sound produced inhibition in the ipsilateral SCM and contralateral SC, allowing the agonist muscle pair to rotate the head toward the stimulated ear.…”

“…Open circles show reflexes whose polarity has either not been definitively determined (triceps and gastrocnemius) or is known to depend upon head position (soleus). Data are from: IO—Weber et al ( 39 ), masseter—Deriu et al ( 40 ), SCM—Colebatch et al ( 8 ), SC—Rosengren et al and Camp et al ( 41 , 42 ), triceps—Cherchi et al ( 43 ), gastrocnemius—Rudisill et al ( 44 ), soleus—Bacsi et al ( 45 ).…”

“…Projections to the splenius capitis (SC) muscles have also been investigated ( 41 , 42 , 49 – 52 ). Splenius is an extensor and rotator located at the back of the neck and acts as an antagonist to the SCM on the same side.…”