Answers are grounded in this paper and cite their sources.
With regard to Nero's last two portrait types, which introduce the coma in gradus formata, various explanations have been given. It is here suggested that the new fashion was the result of the emperor's interest in the stage, and that the crest of stiff locks above the forehead may allude to the coiffures of theatrical masks. Influence from the theatre can also be detected in other manifestations of Neronic fashions and art.
No takes yet. Share an insight, caveat, or question.
Siri Sande (1996) studied this question.
Synapse has enriched 5 related papers. Consider them for comparative context: