The Lombard reflex、a representative auditory feedback mechanism for laryngeal control、occurs when a speaker increases his voice level in response to an increase in the ambient noise level. This reflex has been employed as a clinical tool for determining simulated hearing loss、though the neural mechanisms underlying this reflex remain unclear. In decerebrate cats、repetitive electrical stimulation of the midbrain periaqueductal gray（PAG） induces natural-sounding vocalization. Recently、it has been suggested that audiLory stimulation augments：１）the intensity of voice induced
by stimulation of PAG、and ２）the activities of the laryngeal adductor and expiratory abdominal
muscles. These
results indicate that auditory stimulation has excitatory effects on the activity of the laryngeal adductor and expiratory muscle motoneurons. The Lombard reflex consists of the auditory-laryngeal reflex and the auditory-spinal reflex accordingly. In this study、we aimed to clarify the circuit involved in auditory-laryngeal and auditory-spinal reflexes that may contribute to evocation of the Lombard reflex. Using an electrophysiological technique、an auditory relay projecting its axons to the intrinsic laryngeal motoneurons in the nucleus ambiguus was determined. Consequently、a dorsal nucleus of the lateral lemniscus（LLD） was identified. Moreover、an iontophoretical injection of sodium glutamate to the LLD augmented the activities of intrinsic laryngeal motoneurons. These results indicate that the neurons in the LLD may contribute to the evoking the Lombard reflex.
