Emotional Tears and NGF: A Biographical Appreciation and Research Beginning

Abstract

Emotional tearing is a potent, uniquely human, visual cue that shapes the perception of human facial expression, the

tear effect. The role of tears in emotional signaling was demonstrated by contrasting the perceived sadness of human faces with tears against copies of those images that had the tears digitally removed. Remarkably, faces with tears removed seemed not only less sad but often of neutral emotional valence, showing such expressions as awe, concern, or puzzlement. Emotional tearing is a breakthrough in human sociality that resolves ambiguity and enhances the range and power of the face as a visual signaling medium. Emotional tears are a secondary consequence of lacrimal secretions originally evolved in the service of ocular maintenance and healing. Research from other labs has demonstrated that NGF (nerve growth factor) is elevated in tears and lacrimal glands after corneal injury, and that topical NGF promotes healing of corneal ulcers and may increase tear secretion in dry eye. It is suggested here that NGF and other growth factors may have a role in the evolution and development of the uniquely human capacity to produce emotional tears. The story about emotional tears is presented in the context of a reminiscence of the author’s research mentorship with Rita Levi-Montalcini.