Joe Rogan Experience #1344 - Joseph LeDoux

Here we go. Joe, thank you. Thank you for being here. I really appreciate it, man.

Oh, it's a pleasure to be here.

This is a fascinating subject. I've been really looking forward to talking to you 'cause, uh, the conscious mind and how we, how we evolved our conscious mind, how we have our conscious mind. I mean, that is, uh, one of the more unique things about being a person.

It is.

How did it happen?

Oh. (laughs)

(laughs)

Well, it's only a four-billion-year story, as the subtitle-

Oh, we have some time. (laughs)

... of the book says. (laughs) Good. (laughs) So, shall I tell you how I got-

Sure.

... into it and, uh, where, where, how I ended up thinking about that problem? So I'd been working on how the brain detects and responds to danger for most of my scientific career. Uh, a little bit before that, I'd actually studied consciousness in these people who have their brains split apart to control epilepsy, called split-brain patients. So I got interested in consciousness and also in how behaviors that might be produced non-consciously, uh, affect what we know about ourselves. So, uh, we see ourselves doing something, and then we kind of consciously build that into our narrative of what we are. But a lot of what we do, we do non-consciously. And when we interpret it, that kind of, uh, solidifies the fact that you have a non-conscious system that's controlling your behavior, when in fact you, you didn't do it, but that system did, so you gotta make sense of it and generate an explanation, a narrative. So that, uh, that was where I got started, and I tried to figure out, well, what would be some ki- kinds of non-conscious systems and said, "Well, maybe emotion systems are producing behaviors that we don't fully understand." And I started studying that and ended up, uh, figuring out how this part of the brain called the amygdala receives information about the environment and then controls, orchestrates all the responses, fight-flight kinds of responses to help you protect yourself. And the, um, you know, s- after many years of doing that, I started asking, "Well, how far back does this ability to detect and respond to danger go?" We know that bugs and flies can do that, and research had been done showing that, uh, bugs and flies have certain molecules in their brain that are important in these kinds of protective defensive behaviors and including the ability to learn about them and store those as memories. So it's easier to work on those little tiny, um, uh, invertebrates than it is to do studies in a complex brain, even like a rat brain, which is pretty complex. Um, so given that what these people had discovered about invertebrates, I and others who were studying, uh, mammals decided to see if the same molecules might be involved in mammalian learning, and in fact it was. So now that raises the question, you've got the same molecules doing the same thing, the same molecules, the same genes doing the same thing in ancient invertebrates and in, uh, and animals like us. So you ask, where back in time is the ancestor that made that possible? You know, if we've got the same genes, either it kinda happened spontaneously separately or there's a common ancestor. And indeed there's a common ancestor, and that goes back to the first organism, first animal that had a bilateral body, which means it had a left, right, front, and a back, uh, and a top and a bottom. So it has kind of three-dimensional sides. Before that, there were animals like jellyfish that were radial, they had, but no front and back. They just have a, a top and a bottom. And before that, there's sponges, which have no front, back, top, bottom. They're just kind of randomly organized. So that's kind of the, that's the story of animals, sponges to jellyfish to these bilateral animals. So the ancestor, uh, the, the, the bilateral animal that we're talking about gave rise to those two lines, one that became all these invertebrates like flies and bugs and snails and octopus and all those things, and another to animals like us, vertebrates, all the, um, fish, reptiles, mammals, birds, and so forth. So those are two separate lines that inherited these genes that make the memory and defensive behavior possible. So you say, "Well, how far back then it, does it stop there?" And no, it doesn't because you can find those genes on through jellyfish and then keep going into single-cell organisms. Now, these are like protozoa, uh, things that give you intestinal, um, their, uh, intestinal parasites so they can, you know, give you upset stomach. And, um, things like amoeba, paramecia that you might have heard of in, you know, biology class in high school or something. Um, these have no nervous system, and yet they detect and respond to danger, they learn about their environment, they do all these sorts of things. And where did they come from? Well, if you go all the way back to where they came from, uh, even simpler kind of organism, s- still single-cell, of course, like bacterial cells. Now these guys go back to the beginning of life. The first cell that ever lived some 3.7 billion years ago that gave rise to the entire history of life was a bacterial-like cell that started dividing. Now what's interesting, that cell that started dividing is the mother of every bacterial cell that ever lived. So that cell is, uh, it's, it's more like its rep- you know, that cell is still alive because it's, they reproduce by cell division. So that stell- cell just keeps reproducing, and part of that first cell ever is still with us today in all the bacterial cells that are, that are around. Uh, it's kind of a mind-blowing thing, isn't it? (laughs)