A Role of Neck Afferents on Vestibulocollic Reflex Elicited by Dynamic Labyrinthine Stimulation

Publisher Summary From the frequency response analysis of the vestibulocollic reflex, the existence of a neural integrator was suggested in the pathway between vestibular nucleus neurons and neck motoneurones. The pathways participating in this integration are still unknown. This chapter presents a study on vestibular-induced neck movement (vestibulocollic reflex) with the frequency response method in decerebrate cats. The horizontal semicircular canal was stimulated by sinusoidal oscillation of the turntable. Recordings were made from single motor units or compound EMGs of dorsal neck muscles. Motor units were classified into two groups on the basis of their maximum firing rate: HF (high frequency) and LF (low frequency) units. HF units had a larger gain than LF units. The phase lag of the motor units relative to angular acceleration was about 140°at a frequency range from 0.05 to 0.2 Hz and the gain was decreased at a slope of about 40 dB/decade at a frequency range from 0.01 to 0.4 Hz. A positive correlation was observed between the phase lag and the gain of each motor units.The gain of compound EMG responses depended on the spontaneous activity. When the spontaneous activity was low or too high, the gain was small. There was an intermediate spontaneous activity level at which the gain became maximal.