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.