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Hi everybody. This is our Brain Science Facebook Live session number two. I hope that you will submit your comments and ideas. I want to remind you that I've got a trip to Australia planned for May of 2019, and I hope you'll join me. If you want to know more about the trip, go to brainsciencepodcast.com Australia2019 and you can see the details about the trip, including how much it costs. And if you want a more detailed itinerary, you can send me email@brainsciencepodcastmail.com so what I want to talk about today is peripersonal neurons. In episode 142, I talked about a book called the Spaces Between Us, which was written by Michael Graziano, who's also been on the show in the past. Last month I showed the book, but I don't remember what I did with it, so I apologize for that. Anyway, we first explored this whole idea of peripersonal neurons and peripersonal space back in episode 21 and 23 when we discussed Sandra Blakesley's book the Body Has a Mind of Its Own, how body maps in your brain help you do almost everything better. So that was the first time that I had talked about that famous experiment that shows that when a monkey is taught to use a rake to reach for food, it then incorporates the rake into its body map temporarily. And we think that something like this goes on when we're driving a car and we somehow know where the car is or something that's easier to imagine just using a baseball bat or a tool or tennis racket. So in episode 142, Michael Graziano introduced us to the idea of peripersonal neurons. These are the neurons that have been found in several areas of the brain, and they were found in areas of the brain that they used to think were purely motor, but they actually respond to visual stimuli, specifically objects that are approaching near to the body. He describes these neurons as acting sort of like a bubble wrap, so that if you visualize the bubbles as the receptive fields of the neurons, then there's going to be more bubbles around the head, hands, and arms compared to other parts of the body. These neurons are now known to be multimodal, which means that they can fire both in response to different types of sensory input, such as vision, touch, or sound, but they also participate in motor activity. Initially, Graziano and his colleagues expected that this motor activity was going to be generalized, but eventually they discovered that the specific motor function that these particular peripersonal neurons Appeared to participate in was stereotypical defensive motions that involve things like ducking the head. Now, the early experiments were done on animals that were asleep, and I want to talk about why this is important. First of all, the visual signals that were elicited. The fact that they got visual signals at all Implies that there's some sort of unconscious, automatic process at work. Also, until the mid-90s, this was the standard practice, because the electrodes were so large and bulky and they were too fragile to use in awake animals. This means that any discoveries made during this period really needed to be reproduced in awake, active animals. Another thing that they did that proved to be very important Was that they were moving the objects near the animal Instead of projecting something on a 2D screen. Again, this is important because the standard of the time Was just projecting stuff on screens, and if they hadn't actually moved close to the animal, they would have never detected this firing. Since it specifically involves things happening near the animal, which helps us to understand why everyone didn't discover this sooner. It tells you about how important experimental method can be to what we discover. So these mirror neurons and peripersonal neurons Were first found in the motor areas of the brain. And this was really part of a bigger discovery, which was that neurons can be multimodal. As Graziano said, there's no such thing as a purely motor end of the system. I want to emphasize that this means that splitting the brain into motor areas and sensory areas Is a gross oversimplification, Even though this is the way it's still taught in the neuroanatomy that medical students learn. So one of the things to understand about all this, the work was done in monkeys. The reason was that monkeys have visual systems that seem to be pretty similar to ours. And so a lot of work has been done on their systems. Now, you might go, oh, well, that's just obvious that they're similar, but their auditory systems are significantly different from ours. These monkeys don't even learn how to respond to their own names. They don't have language, Even though some species of monkeys can have isolated calls that represent certain things, like, say, snakes or other kinds of predators. So what happened when they started working with the monkeys that were awake? One of the things that they learned was that if they put the monkey in the dark, Turned out the lights, that the monkey would remember the last location that they saw the object, and that's where they expected the object to be. So I mentioned that they were initially thinking that these peripersonal neurons Were going to be doing all kinds of motor things. And this is one of the things that they missed, the clues about what they were really doing, because they had certain expectations. And this is something that happens in science. Science is done by humans. Humans have expectations, and sometimes they can miss the obvious clues in experimental data. That's the reason why it's important to be able to go back and look at data again in the light of new ideas. Now, eventually, they moved on to doing brain stimulation studies. And here again, a key was that they did not follow the sort of traditional standard technique, partly because they didn't come from that field. And so they didn't know. Well, everybody does 10, 20 milliseconds. Well, probably they did know. But the 10 to 20 millisecond idea of stimulation was based on wanting to isolate it down to the smallest possible stimulation, whereas they chose a 500 millisecond time range because that was how long it takes a typical motor activity to be stimulated. And so, instead of seeing isolated twitches, they saw whole movements. This is what allowed them to see and discover those stereotypical defensive movements. Now, they actually found a whole suite of movements, some of which are similar to the ones that the people studying mirror neurons discovered, but the peripersonal neurons were the ones that were related to the defensive movements. Now, in contrast, the mirror neurons, which you've probably all heard of, those are the ones that respond to seeing a certain thing done and also are active when you're doing a certain thing. So just to put this into a larger context, as I mentioned, they did discover a whole repertoire of movements. And as I mentioned, that famous Erke classic study with the monkeys using the rakes, I originally mentioned that back in episode 21. So I'm going to come back to that in just a second, but I want to just finish up my summary of the episode. Dr. Graziano's son's story of dyspraxia, which he talked about briefly during the interview and also talks about in some detail in his book. It emphasizes the importance of peri Impersonal neurons. We take this system for granted, partly because it's unconscious, partly automatic. But as his son's story shows, even simple activities like sitting in a chair or eating with a fork become difficult if there's a malfunction in this system. Now, this live thing is kind of new, and people haven't gotten into the habit of tuning in or sending me questions yet. I've started to get some questions for some more recent episodes. So I'm hoping that as time goes on, when I do these Facebook Live. My plan will be to do like I just did, a brief episode summary and then address questions and feedback from the audience. For today, the only thing I really have was some audio feedback that Darrel sent me. And what I'm going to try to do is I'm going to try to play this off of my phone into the microphone, and I apologize. It's pretty short. So if it turns out you can't hear it, well, I'm going to sort of hit the high points after it's done. So here goes.