India, July 5 -- How does one explain the exhilaration and fear of moving to a new city? The ache of sadness and gratitude at the end of a long-awaited trip? The grief and relief just after a breakup?

Can people truly feel both positive and negative emotions at the same time, or do we just rapidly flip back and forth between them?

For over 150 years, neuroscientists and researchers have been trying to answer this question, not just because it is intriguing, but because it has implications for how we deal with risk, navigate new experiences, and process input from our world.

Before we unpack some of this, a brief look back.

Since Charles Darwin's publication of The Expression of the Emotions in Man and Animals in 1872, emotions have be...