According to Barrett, alexithymia is a condition that affects about 10% of the population. People with alexithymia have “an impoverished conceptual system for emotion” (107) and struggle to clearly experience emotions themselves. Barrett emphasizes the connection between their inability to remember emotion words and their struggle to feel emotion concepts, adding that their sensations often manifest more physically, such as feeling a stomachache rather than anger.

Degeneracy is a term neuroscientists use to refer to the fact that neurons can combine in different ways to create the same outcome in the brain. Barrett explains that this phenomenon is highly relevant to the study of emotion, since varied brain activity can somehow produce the same emotion in the thinker.

Emergent properties are phenomena our brains produce that are more than the sum of their parts. This makes it difficult to identify and study specific brain regions, since we can’t isolate them from their many neural connections and the many outcomes they produce by working together.