LOMBARD REFLEX DURING PAG-INDUCED VOCALIZATION IN DECEREBRATE CATS

The Lombard reflex occurs when a speaker increases his vocal effort wh ile speaking in the presence of ambient noise. The purpose of this stu dy was to clarify whether the Lombard reflex can be evoked during cont rolled vocalization in an animal model. In decerebrate cats, repetitiv e electrical stimulation was applied to the midbrain periaqueductal gr ay (FAG) to evoke vocalization. Pure tone auditory stimulation was del ivered through a loudspeaker. The activities of the laryngeal adductor muscle, diaphragm and external oblique abdominal muscle and the voice intensity were measured during FAG stimulation, in the presence and a bsence of the auditory stimulation. To clarify the effects of the audi tory-laryngeal reflex on the activity of laryngeal adductor motoneuron s, the amplitude of the laryngeal reflex evoked by single shock stimul ation of the superior laryngeal nerve was also measured during respira tion? in the presence and absence of auditory stimulation. The sound m ade by the cats due to FAG-induced vocalization was augmented by expos ure to auditory stimulation, and the activities of the laryngeal adduc tor muscle and external oblique abdominal muscle were also augmented. During respiration, auditory stimulation also increased the amplitude of the laryngeal reflex evoked in the laryngeal adductor muscle. These results demonstrate that the essential neuronal mechanisms for evokin g the Lombard reflex exist within the brainstem. (C) 1997 Elsevier Sci ence Ireland Ltd.