C-fos expression during vocal mobbing in the new world monkey Saguinus fuscicollis.

In order to find brain areas involved in the vocal expression of emotion, we compared c-fos expression in three groups of saddle-back tamarins (Saguinus fuscicollis). One group, consisting of three animals, was made to utter more than 800 mobbing calls by electrical stimulation of the periaqueductal grey of the midbrain (PAG). A second group, consisting of two animals, was stimulated in the PAG with the same intensity and for the same duration as the first group but at sites that did not produce vocalization. These sites lay somewhat medial to the vocalization-eliciting sites. A third group, consisting of two animals, was stimulated at vocalization-eliciting sites in the PAG but with an intensity below vocalization threshold. Fos-like immunoreactivity that was found in the vocalizing but not in the non-vocalizing animals was located in the dorsomedial and ventrolateral prefrontal cortex, anterior cingulate cortex, ventrolateral premotor cortex, sensorimotor face cortex, insula, inferior parietal cortex, superior temporal cortex, claustrum, entorhinal and parahippocampal cortex, basal amygdaloid nucleus, anterior and dorsomedial hypothalamus, nucleus reuniens, lateral habenula, Edinger-Westphal nucleus, ventral and dorsolateral midbrain tegmentum, nucleus cuneiformis, sagulum, pedunculopontine and laterodorsal tegmental nuclei, ventral raphe, periambigual reticular formation and solitary tract nucleus. For some of these structures (e.g. anterior cingulate cortex and periambigual reticular formation), there is evidence also from electrical stimulation, lesioning and single-unit recording studies that they are involved in vocal control. For other structures (e.g. lateral habenula, Edinger-Westphal nucleus), the available evidence speaks against such a role. Fos activation in these cases is probably related to non-vocal reactions accompanying the electrically elicited vocalizations. A third group of structures consists of areas for which a role in vocal control cannot be excluded but for which the present study presents the first evidence for such a role (e.g. claustrum and sagulum). These structures deserve further studies using more specific methods.