THE ROLE OF THE PERIAQUEDUCTAL GREY IN VOCAL BEHAVIOR

This is a review of our current knowledge about the role of the periaq ueductal grey (FAG) in vocal control. It shows that electrical stimula tion of the FAG can evoke species-specific calls with short latency an d low habituation in many mammals. The vocalization-eliciting region c ontains neurones the activity of which is correlated with the activity of specific laryngeal muscles. Lesioning studies show that destructio n of the FAG and laterally bordering tegmentum can cause mutism withou t akinesia. Neuroanatomical studies reveal that the FAG lacks direct c onnections with the majority of phonatory motoneurone pools but is con nected with the periambigual reticular formation, an area which does h ave direct connections with all phonatory motor nuclei. The FAG receiv es a glutamatergic input from several sensory areas, such as the super ior and inferior colliculi, solitary tract nucleus and spinal trigemin al nucleus. Glutamatergic input, in addition, reaches it from numerous limbic structures the stimulation of which also produces vocalization , such as the anterior cingulate cortex, septum, amygdala, hypothalamu s and midline thalamus. Pharmacological blocking of this glutamatergic input causes mutism. The glutamatceptive vocalization-controlling neu rones are under a tonic inhibitory control from GABAergic neurones. Re moval of this inhibitory input lowers the threshold for the elicitatio n of vocalization by external stimuli. A modulatory control on vocaliz ation threshold is also exerted by glycinergic, opioidergic, cholinerg ic, histaminergic and, possibly, noradrenergic and dopaminergic affere nts. It is proposed that the FAG serves as a link between sensory and motivation-controlling structures on the one hand and the periambigual reticular formation coordinating the activity of the different phonat ory muscles on the other.