NEURAL CONTROL OF VOCALIZATION - RESPIRATORY AND EMOTIONAL INFLUENCES

Previous research has shown that a region of the midbrain, the periaqu eductal gray matter (FAG), is critical for vocalization. In this revie w, we describe the results of previous investigations in which we soug ht to find out how FAG neurons integrate the activity and precise timi ng of respiratory, laryngeal, and oral muscle activity for natural-sou nding vocalization using the technique of excitatory amino acid microi njections in cats. In these studies, all surgical procedures were carr ied out under deep anaesthesia. In the precollicular decerebrate cat t wo general types of vocalization, classified as voiced and unvoiced, c ould be evoked by exciting neurons in the lateral part of the intermed iate part of the FAG. The patterns of evoked electromyographic activit y were strikingly similar to previously reported patterns of human mus cle activity. Coordinated patterns of activity were evoked with just-t hreshold excitation leading to the conclusion that patterned muscle ac tivity corresponding to the major categories of voiced and voiceless s ound production are represented in the FAG. In a parallel series of hu man and animal experiments, we also determined that the speech and voc alization respiratory patterns are integrated and coordinated with aff erent signals related to lung volume. These data have led to the propo sal of a new hypothesis for the neural control of vocalization: that t he FAG is a crucial brain site for mammalian voice production, not onl y in the production of emotional or involuntary sounds, but also as a generator of specific respiratory and laryngeal motor patterns essenti al for human speech and song.