Summary5 min read

Brain Science Live #2 — Understanding Peripersonal Neurons and the Body’s Spatial Buffer

Podcast: Brain Science with Ginger Campbell, MD
Host: Ginger Campbell, MD
Date: July 15, 2018
Episode: Brain Science Live #2

Episode Overview

Dr. Ginger Campbell leads this live episode by diving into the neuroscience of peripersonal neurons—the brain cells that help define our personal space and extend our awareness to tools and vehicles we employ. The discussion builds on previous book reviews and episodes, notably Michael Graziano’s The Spaces Between Us and earlier explorations of body mapping in the brain. Dr. Campbell also addresses listener feedback regarding the computational aspects of spatial buffering and the bodily sense of self.

Key Discussion Points and Insights

1. Introducing Peripersonal Neurons and Space

Dr. Campbell references her previous discussions on peripersonal space and body mapping, outlining how these brain systems help us “know” where our body—and anything we use, like tools—is in relation to the world.
Peripersonal neurons were first understood through experiments with monkeys, notably when a monkey uses a tool (like a rake) and the brain’s map temporarily expands to include that tool (00:58).

“This 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.” — Dr. Campbell [01:32]

Dr. Campbell stresses how such processes are similar when driving a car or wielding a baseball bat, illustrating how our brains adapt to tools by expanding our “spatial bubble.”

2. Multimodal Nature and Defensive Movements

Peripersonal neurons are found in parts of the brain once considered “purely motor” but in fact respond to multiple sensory inputs—vision, touch, sound—as well as motor activities.
Early beliefs: motor areas and sensory areas are strictly separate. New understanding: such a split is a gross oversimplification (04:13).

“As Graziano said, there’s no such thing as a purely motor end of the system.” — Dr. Campbell [05:05]

Notably, these neurons are critical in organizing stereotypical defensive actions—reactions like ducking or blocking—that occur when something approaches the body (03:45).
The “bubble wrap” analogy: receptive fields of peripersonal neurons cluster densely around vulnerable spots like the head and hands.

3. Experimental Methods in Discovery

Initial discoveries used anesthetized animals due to the technical limitations of electrode size and fragility in the 1990s (05:33).
Innovations included moving objects physically near the animal, not just showing images on a screen, which was key to triggering these neuron responses (06:08).

“It tells you about how important experimental method can be to what we discover.” — Dr. Campbell [06:23]

As methods advanced, awake monkey studies revealed that monkeys could remember where an object last appeared even in the dark (07:25).

4. Brain Stimulation Techniques and Findings

Traditional studies used short bursts (10–20 ms) of stimulation. Graziano’s team used longer (500 ms) durations, better matching natural movement timescales, revealing complex defensive responses vs. simple twitches (08:13).

“This is what allowed them to see and discover those stereotypical defensive movements.” — Dr. Campbell [08:35]

Comparison to mirror neurons:
- Mirror neurons fire both during action execution and when seeing the same action.
- Peripersonal neurons are specialized for nearby, space-related, defensive actions.

5. Real-life Implications & Dyspraxia

Dr. Campbell mentions Michael Graziano’s son’s struggles with dyspraxia, emphasizing how unconscious these bodily systems usually are—and how disruptive their malfunction can be to everyday activities (09:24).
Example: actions as simple as sitting in a chair or eating can become difficult.

Listener Feedback Segment (10:04–11:59)

1. Darrell’s Question on the “Spatial Buffer”

Darrell Fergus asks for more details on the spatial buffer—the peripersonal zone, especially as it wraps around tools or vehicles—and the computational mechanics behind it.

“I also continue to propose that the, what I call the egocentric body … is the deep source of the proprioceptic whole body, is the source of the self. … We try to teach in movement skills, and I tried to teach in my gymnast.” — Darrell Fergus [10:37]

Darrell links his coaching experience in gymnastics with concepts of proprioception and body-centered selfhood.

2. Dr. Campbell’s Response

She highlights the technical and computational challenges of studying large-scale neural processing during the original research era (the 1990s), noting that most neuroscientists then lacked advanced computational tools (12:07).
Recognizes agreement with Darrell: our sense of self is fundamentally rooted in the body.

“I agree with your basic idea that our sense of self is very body centered. I think that that’s hard to argue with.” — Dr. Campbell [12:35]

She refers to out-of-body experiences as examples of how the brain constructs a sense of self from integrated (or mismatched) bodily signals.
Announces future coverage of computational neuroscience developments in upcoming episodes, specifically mentioning Eve Martyr’s work.

Notable Quotes & Memorable Moments

On discovery methods:
“It tells you about how important experimental method can be to what we discover.” — Dr. Campbell [06:23]
On brain mapping with tools:
“The monkey would remember the last location they saw the object, and that’s where they expected the object to be.” — Dr. Campbell [07:28]
On the sense of self:
“I agree with your basic idea that our sense of self is very body centered.” — Dr. Campbell [12:35]
Darrell’s insight on teaching movement:
“We try to teach in movement skills, and I tried to teach in my gymnast. … That’s the real ground of this spatial buffer that wraps around tools and things.” — Darrell Fergus [10:37]

Timeline of Key Segments

00:04 — Introduction & announcement of Australia trip
00:58 — Peripersonal neurons and prior episode/book references
03:45 — Defensive actions & “bubble wrap” analogy
05:05 — Multimodal nature and revisiting brain area distinctions
06:08 — Experimental methods leading to discovery
08:13 — Brain stimulation techniques reveal defensive movements
09:24 — Real-life dyspraxia example
10:04 — Listener Darrell’s audio feedback on spatial buffer
11:59 — Dr. Campbell’s reply on computation and bodily self

Closing Thoughts

Dr. Campbell’s accessible yet nuanced review of peripersonal neurons demystifies how our brains blur the boundary between “me” and the objects or tools we use, explaining the ancient and adaptable roots of our spatial self-awareness. Listener engagement brings fresh, practical connections to movement science and the sense of the embodied self, reminding us how deeply neuroscience concepts link to everyday life.

For more on future topics and episodes (like computational neuroscience with Eve Martyr), check Brain Science’s episode feed.

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Transcript3 lines

[00:04]
A
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.
[10:04]
B
Hi, Ginger. Darrell Fergus with a fast question for the Next live presentation, July 5. Mine concerns what he called the spatial buffer. The wraparound of the spatial buffer, and it wraps around tools, it wraps around driving a car, and that idea of a spatial buffer. He then further. You asked him about the computation or what processing, directed this could be directing. Where did this spatial buffer come from? I'd like to know more about that. And I also continue to propose that the, what I call the egocentric body, and I propose that for my gymnastics character is the source of the proprioceptic whole body is the source of the self. It's the source of. It's the bottom line. Things rebound, cells rebound. The whole body rebounds. It has a center of mass. It has a velocity. We teach that, we feel it, we get students to feel it. And I somehow believe that is the deeper thing he's talking about. At least that's my hypothesis. That's the real ground of this spatial buffer that wraps around tools and things. It's a very connected process. We try to teach in movement skills, and I tried to teach in my gymnast. There you go. Have a great show. Maybe I took too long. Have a great one, Ginger. Cool. Great job.
[12:00]
A
So I really wanted to play that because Darrell's been a loyal listener for a long time and we've had a lot of exchanges about the role of proprioception and. And how neuroscience might inform practices such as gymnastics. And I've always found his take on my show fascinating, and it's always been a source of inspiration to me. I don't know much about the computation involved, and I don't think Dr. Graziano does either because at the time that Dr. Graziano was doing his work with these single cell neurons, this was really more back in the 90s when computers were a lot slower than they are now, and it really wasn't possible to process the data from more than a few neurons at a time. So trying to figure out this kind of computational stuff was limited not only by the computers, but by the fact that most neuroscientists don't have the computational skills. This is an area that's really growing in importance. And I'm going to be talking about this more in this month's episode which is going to feature the work of Eve Martyr. But I agree with Darrel, I agree with your basic idea that our sense of self is very body centered. I think that that's hard to argue with. And after all, the whole out of body experience has to do with when the brain gets mismatched signals that it then interprets as an out of body experience because it's the only way it can make sense out of the mismatched signals. So I haven't gotten any extra comments today, but as I said, I hope that as time goes on, more and more people will participate and give me ideas that I can incorporate into making this a little bit of a longer adventure. But I appreciate you listening today. And the other thing that I'm going to repeat, because it's important is the next episode of Brain Science will be in the feed on the last Friday of July. And as I said, it's going to be about Eve Martyr's work. And the other thing is, if you want to come with me to Australia, please check out the information on my website@brainsciencepodcast.com Australia2019 I'm planning to take 16 people, the first 16 people that sign up and pay their deposits. And I think it's going to be a great trip and a chance for us to get together and geek out on the brain. So I'm going to sign off for now next month. I'll be back again on the first Thursday of the month at 8pm Central time to talk about episode 143, which is about language in the brain. Thanks for listening. Brain Science with Dr. Ginger Campbell is copyright 2018 to Virginia Campbell, MD. You can copy this show to share it with others, but for any other uses or derivatives, please contact me@brainsciencepodcastmail.com.