This sentence strikes me as odd, because subjectively, the one thing that shines through the most with people, even people I haven't seen in 20+ years, is a distinct (and possibly largely immutable) personality. In fact, a large part of why I was so shy growing up is because people's personalities were so "bright" that I felt intimidated. Not of course "bright" in a literal, measurable sense, but in an irrational qualitative sense. And therein lies the problem with trying to discuss it rationally.
To this day I perceive distinct personalities in every child and pet I encounter. Not sure if related, these exact same entities seem drawn to me for some reason. I have often heard a pet owner say "my pet has never acted this way before" around me (such as sitting in my lap when it has never done so with anyone).
I wonder if it simply reflects what I see in them. Anyway. My point is that the inability to discuss something rationally is not evidence for its nonexistence.
They claimed there's simply an absence of unambiguous evidence that it exists.
My argument is then that we will never have evidence that it exists because evidence is rational and objective and its very reality and/or value is trapped in the irrational subjective eye of the beholder.
Trying to boil it down into, say, patterns of neuron activations would be like trying to boil down or derive the "value reality" of the Mona Lisa by analyzing and cataloguing the light wavelengths reflecting off of it.
The episode talks about research showing how we can understand ourselves better as sets of behavior that we exhibit in different contexts, more than as having a single personality.
Put in simple words, you maybe introvert in some contexts and extrovert in others, and theses behaviors can change over time. You ARE not AN introvert, you exhibit introvert behaviors in context.
[1]: http://www.npr.org/programs/invisibilia/482836315/the-person...