Motor organization of positive and negative emotional vocalization in the cat midbrain periaqueductal gray

Hari H Subramanian, Mridula Arun, Peter A Silburn, Gert Holstege

Neurochemical microstimulation in different parts of the midbrain periaqueductal gray (PAG) in the cat generates four different types of vocalization, mews, howls, cries and hisses. Mews signify positive vocal expression while howls, hisses and cries signify negative vocal communications. Mews were generated in the lateral column of the intermediate PAG and howls and hisses in the ventrolateral column of the intermediate PAG. Cries were generated in two regions, the lateral column of the rostral PAG and the ventrolateral column of the caudal PAG. In order to define the specific motor patterns belonging to mews, howls and cries, the following muscles were recorded during these vocalizations; larynx (cricothyroid, thyroarytenoid and posterior cricoarytenoid), tongue (genioglossus), jaw (digastric) and respiration muscles (diaphragm, internal intercostal, external abdominal oblique and internal abdominal oblique). Further, the frequency, intensity, activation cascades, turns and amplitude analysis of the electromyograms (EMG's) during these vocalizations were analyzed. The results show that each type of vocalization consists of a specific circumscribed motor coordination. The nucleus retroambiguus (NRA) in the caudal medulla serves as the final premotor interneuronal output system for vocalization. NRA neurochemical microstimulation also generated vocalizations (guttural sounds). Analysis of their EMG's demonstrated that these vocalizations consist of only small parts of the emotional vocalizations generated by neurochemical stimulation in the PAG. These results demonstrate that motor organization of positive and negative emotional vocal expressions are segregated in the PAG and that the PAG uses the NRA as a tool to gain access to the motoneurons generating vocalization. This article is protected by copyright. All rights reserved.