What Do Phantom Limbs and Lifting Have in Common?

Phantom Limbs and Proprioception

By: Nick Soleyn, PBC

A young man sits blindfolded on an exam table as a neuroscientist prods him with a Q-tip. Doctors had already confirmed that nothing neurological was wrong with him. Yet, when the scientist touches certain parts of his face, the young man reports sensations in his left hand, surprising the researcher and startling the man himself. Compounding the strangeness of dual sensations on his face and hand is the fact that the hand itself doesn’t exist. Three weeks earlier, the young man lost his arm in a car crash. Professor V.S. Ramachandran uses this story in both his research on phantom limbs and in his book, “The Tell-Tale Brain: A Neuroscientist’s Quest for What Makes us Human”:

“For most parts of the body, he reported the location of the sensation accurately. But when we touched his ipsilateral face, he reported with considerable surprise that he felt the touch not only on his face—as expected—but also on his missing phantom hand. Touching different parts of the face elicited precisely localized sensations on different parts of the phantom arm. The margins of different fingers were clearly delineated, and there was a crudely topographic organization. Stroking the cheek was felt as stroking on the phantom, and tapping was felt as tapping.” (V.S. Ramachandran and Eric L. Alschuler, “The use of Visual Feedback, in Particular Mirror Visual Feedback, in Restoring Brain Function,” Brain 2009: 132; 1693–1710.)

Like an additional clue in the complex mystery of how the human brain operates, the concepts of phantom limbs and phantom pain provide an anomaly that neuroscientists must account for when trying to explain how we perceive and control our bodies.

Proprioception is the mind’s sense of the body’s position and movement. It lets us manipulate objects that are out of sight, helps us know the location of our limbs even when blindfolded, and even helps us learn to lift barbells. One of the key components of lifting is controlling our bodies as they are challenged to hold certain postures, move in a coordinated fashion, and maintain balance. While all that might seem relatively straightforward, experiences like the young man’s phantom limb have caused scientists to probe deeper into the things that give us a sense of self and control over our bodies, which in turn can help us become better lifters and better athletes.

Proprioception

Proprioception involves multiple feedback loops. Your body has many pathways for sensory inputs, including receptors in your skin, muscles, and bones. These receptors provide real-time information to your brain. If that were the whole picture of proprioception, we would expect that when a person loses a limb, the sensory input would just go dark. Instead, amputees often experience pain in their missing limbs or even the sensation of being able to move them.

In addition to sensory inputs, your brain contains a sensory map of the positioning and layout of your body. In general, particular areas of your sensory cortex correspond to the positions of receptor cells in your skin, muscles, and joints. The image below attempts to illustrate the proximity and prevalence of sensory inputs. Note that the hand and face are close together, perhaps helping to explain the phantom sensations of the young man who felt the q-tip on his face and missing limb simultaneously.

In The Tell-Tale Brain, professor Ramachandran discusses probably reasons for a faulty map in amputees. “Even though the map is accurate for the most part, some portions of it are scrambled with respect to the body’s actual layout.” He also explains how he has used the mapping tendencies of the brain to help alleviate phantom pain or even “amputate” phantom limbs. “There is no longer an arm, but there is still a map of the arm in the brain. The job of this map, its raison d’etre, is to represent its arm. The arm may be gone, but the brain map, having nothing better to do, soldiers on. It keeps representing the arm, second by second, day after day.” Where the brain is looking for sensory input from the missing arm, it might find a substitute—a touch on the face, for example.[1]

“The subject of proprioception lies at the boundary between neurophysiology and neuropsychology.” (Uwe Proske, and Simon C. Gandevia, “The Proprioceptive Senses: Their Roles in Signaling Body Shape, Body Position and Movement, and Muscle Force,” https://doi.org/10.1152/physrev.00048.2011.) An amputee experiencing a phantom limb or researchers observing the faulty perception of a person’s movement or limbs exposes the complex, though often unnoticed, nature of our sense and control of movement and being. Ideally, your map is accurate with no dark, unexplored areas. If you want to move your arms, open a door, or push the pedals of your car without visual feedback, you should be able to do so.

We use this sense map when we engage in barbell training. One of the first things you will do when you first start lifting is to place a bar on your back, out of sight. Your eyes stay focused on a point on the floor, and you learn to squat, moving an object through space without looking. It is actually easier to squat and maintain your balance without visual feedback, such as a mirror, relegating control to your sense and your internally held model of the movement.

If you had never squatted before, the first rep (or first dozen) would be a little tricky. Most new lifters will say that there’s “a lot to think about” when you are trying to lift. That is because your map is being refined in new ways. With good feedback and deliberate practice, you learn how a squat is supposed to feel. Then, there is less to think about.

The Mirror Box

Suppose now we have to troubleshoot the map of your body that you hold in your mind. While the ability to control a barbell in space, perform unfamiliar movements, and do seemingly simple things, like set and hold your back in rigid extension, are much less dramatic, we can perhaps learn something from the treatment and experience of phantom limbs. Professor Ramachandran learned to manipulate how the brain develops a “central body map” to help amputees like the young man we discussed earlier. And he did so using a relatively low-tech method.

Professor Ramachandran describes his approach to treating phantom limbs as first understanding the source of feeling from the limb. “Motor output signals to the muscles are (in effect) cc’d to the parietal lobes, where they are compared to sensory feedback signals from the muscles, skin, joints and eyes. If the parietal lobes detect any mismatches between the intended movements and the hand’s actual movements, they make corrective adjustments to the next round of motor signals.” When a limb is amputated, these command centers are on “autopilot,” and, somewhat paradoxically, this part of the brain does not access your rational knowledge that the limb is missing. The command centers continue to send motor signals to the limb and cc’d signals to the mapping part of your brain where they are misinterpreted as actual movements of the phantom limb.

The brain doesn’t know what it doesn’t know, and in these extreme cases, it lacks reliable sensory input to help it learn. He addressed this problem by offering a different kind of sensory input to help the brain learn and adjust. He created what is known as a ‘mirror box. He writes,

“I placed an upright mirror in the center of a cardboard box whose top and front had been removed. If you stood in front of the box, held your hands on either side of the mirror and looked down at them from an angle, you would see the reflection of one hand precisely superimposed on the felt location of your other hand. In other words, you would get the vivid but false impression that you were looking at both of your hands; in fact, you would only be looking at one actual hand and one reflection of a hand.”

By having patients visually experience their phantom limb, some were able to move painfully “frozen” limbs and find relief. Others, with some prolonged use of the mirror box, removed the phantom limbs from their perception altogether, in effect amputating the phantom limb. Professor Ramachandran and others have demonstrated that the brain is susceptible to additional sensory input, which, when used strategically, can either trick the brain into a false reality such as moving phantom limbs or update its central body map.

Body Image and Body Schema

Mirror therapy has become widely used in clinical settings as it is cheap and effective in treating different types of motor issues and pain, particularly in stroke patients (Dohle, “Mirror Therapy”). Its clinical use and similar experiments with virtual reality have added dimensions to the theoretical aspects of the science behind movement. [2] The old view of proprioception treated the brain more like a computer made up of autonomous, specialized modules that turned sensory inputs into motor outputs. A kind of one-to-one connection between what happens to you and how you react. Dysfunction, according to this model, simply means that a person has lost one of these modules.

That traditional view couldn’t quite explain certain clinical phenomena, however. One doctor might report a stroke patient who couldn’t detect a touch on an impaired hand but could readily point to where he had been touched with his other hand, while another would report a stroke patient who could sense a touch but seemed unable to point to its location.[3] These phenomena (called double disassociation) were eventually replicated in clinical settings. In one of these tests, two patients sat with their hands in front of them, palms down on the table. In front of them, researchers placed a drawing of their own impaired hands. The subjects each received taps on their impaired hands “using tactile stimuli far above the detection threshold.” They were then asked to locate the taps by pointing to their hands and to the line drawing. One patient was unable to show where he had been touched on his own hand but could identify the spot on the drawing. The other patient was exactly the opposite, showing impairment in identifying stimulus on the drawing but being able to point to the point of stimulus on her own hand (Anema, 2009). Cases like these helped give rise to the idea that, rather than specialized modules determining functions, there are at least two interrelated aspects of proprioception: a body image and a body schema.

Body image is like the line drawing of the hands or Dr. Ramachandran’s map. It is both the conscious understanding of our body and the expectations that extend from that image, giving us a sense of what parts are our own and an awareness of movement. Though powerful, it is not particularly difficult to fool the body image. Just watch the rubber hand illusion below.

Body schema, on the other hand, is an automatic, reactive system based mostly on sensory inputs and controlling things like posture and movement (Gallagher 2001). These systems are interconnected. The experiences that build your body image come, in part, from the sensory inputs and practicing movement, and “the actions controlled by the body schema can be precisely shaped by the intentional experience or goal-directed behavior of one’s own body” (Matamala-Gomez, 2019).

Combining Sensations

There is some parallel, then, between phantom limbs and athletic movements, such as those we use when barbell training. The goal of any skilled movement is to move or react in a manner consistent with your intent. Consider the model of the squat. A bar is placed on your back, and you are asked to move it in a straight vertical line while maintaining your balance and controlling specific muscle groups, like your spinal erectors, to ensure the safe and effective transmission of force that will allow you to move the unseen (but definitely felt) barbell.

Physical skills require some combination of learned experience and reaction to the sensory inputs during the movement itself. For someone experiencing a phantom limb, whether that person’s phantom moves or is frozen in place often depends on whether the limb was paralyzed before amputation. The brain’s experience sets the expectations for the movement. Experienced lifters have to think less about specific aspects of a lift than novices, just as experienced athletes seem to have improved reaction times based on less information than novice athletes.

Where experience is lacking, one must learn. While you should eschew mirrors when lifting—they distract from the body schema aspect of lifting—we can use some lessons from Professor Ramachandran’s mirror box experiments: additional sensory feedback to establish the correct movement helps train your brain in what the correct movement should feel like. Stated otherwise, visual and other types of experiential or knowledge-based information can help improve the mental model that you hold of each of the lifts.

Developing your proprioceptive senses requires feedback about how the lift or movement feels during or shortly after its execution. If you think a lift feels correct and a coach confirms that sensation, you can attempt to replicate that feeling. If a movement feels correct to you, but a knowledgeable coach or friend tells you otherwise, you know that you need to make a change to how the lift feels through deliberate practice.

Similarly, the tactile sense of learning often relates to how you control individual body parts. Learning how to extend one’s lumbar or thoracic spine and maintain that extension often is a challenging concept. One can learn this movement through tactile feedback—a hand placed in the correct spot—along with a verbal or visual cue. The sense of touch is a powerful one when it comes to creating and updating your central body map.

Visual confirmation of a movement can come from many sources. You should video all your work sets. The video can help you identify errors and confirm correct good reps. Helping you make changes or reinforcing your mental model of the lift. Visual confirmation requires that you have some knowledge of what the movement should look like and how to correct errors.

These lessons apply to most physical skills. The lifts we perform can feel awkward and clumsy, like trying to manipulate a body part you didn’t know existed before you attempted to squat for the first time. If you approach the lifts as a collection of sensory inputs and experience, you will help direct your efforts toward better learning and better movement in no time.

NOTES

[1] From the Tell-Tale Brain:

“Finally, after amputation of the foot of another patient, sensations from the penis were felt in the phantom foot. (Indeed, the patient claimed that his orgasm spread into his foot and was therefore “much bigger than it used to be.”) This occurs because of another of these odd discontinuities in the brain’s map of the body: The map of the genitals is right next to the map of the foot.”

[2] See, e.g., Marta Matamala-Gomez, Tony Donegan, Sara Bottiroli, Giorgio Sandrini, Maria V. Sanchez-Vives, and Cristina Tassorelli, “Immersive Virtual Reality and Virtual Embodiment for Pain Relief,” Front. Hum. Neurosci., vol. 13 art. 279 (Aug. 2019)

[3] Anema, 2009 (citing Paillard, Jacques & Michel, Francois & Stelmach, George, “Localization without content: A tactile analogue of ‘blind sight’,” Archives of neurology, 40, 548-51 (1983) and Halligan, Hunt, Marshal, Wade, “Sensory detection without localization,” Neurocase, 1, 259–266 (2006)).

References

Anema, van Zandvoort, de Haan, Kappelle, de Kort, Jansen, Dijkerman, “A double dissociation between somatosensory processing for perception and action,” Neuropsychologia, May;47(6):1615-20 (2009).

Christian Dohle, Eric Altschuler, Vilayanur S. Ramachandran, “Chapter 20 – Mirror therapy,” Editor(s): K. Sathian, V.S. Ramachandran, “Multisensory Perception,” P. 449-61, Academic Press (2020).

Gallagher, “Dimensions of embodiment: body image and body schema in medical contexts,” Br. J. Clin. Pharmacol., 68, 147–175 (2001).