Can you still feel a limb that's gone? - Joshua W. Pate

Summary

Phantom limb sensations occur when amputees or even those born without a limb experience vivid, sometimes painful, sensations of a missing body part. This phenomenon is tied to the brain's internal map of the body, which remains intact after amputation. Changes in nerve pathways and cortical representation contribute to these sensations. Treatments like mirror box therapy and prosthetics can help reduce pain and enhance functionality. Further research on phantom limbs offers insights into how our brains construct reality, highlighting the subjectivity of perception.

Takeaways

• 🧠 Phantom limbs are experienced by most people who lose a limb, and they feel realistic, not just as memories or vague shapes.
• 👶 Even people born without limbs can sometimes experience phantom limb sensations, suggesting we are born with a body map in the brain.
• 🩹 Phantom limbs are often painful, setting them apart from the limbs they replace.
• 🦾 Sensory neurons, which transmit signals from the body to the brain, remain mostly intact after amputation, affecting the way signals travel.
• ⚡ Severed nerve endings can become overly sensitive after amputation, sending pain signals even in response to mild stimuli.
• 🗺️ The somatosensory cortex, where the body is mapped, processes these sensory signals. Larger areas are dedicated to more sensitive body parts, like hands and lips.
• 🎻 The brain can adapt its cortical map depending on use or injury—violinists, for example, have a larger representation of their left hand in the brain.
• 🪞 Mirror box therapy can help reduce phantom limb pain by tricking the brain into seeing the missing limb.
• 🦿 Prosthetics can also reduce phantom pain, and patients may perceive them as natural extensions of their bodies.
• 🔍 Understanding phantom limbs offers insights into how the brain constructs the subjective realities we perceive daily.

Q & A

What is a phantom limb sensation?

A phantom limb sensation is the feeling that an amputated or missing limb is still present, often with vivid detail and sometimes pain.

Why do some people feel phantom limbs even if they were born without them?

The fact that some people born without a limb can feel a phantom suggests that we are born with at least the beginnings of a body map in our brains.

How does the loss of a limb affect the neural pathways?

The loss of a limb alters the way signals travel through the neural pathways, causing severed nerve endings to become more sensitive and transmit distress signals.

What is the role of the dorsal horn of the spinal cord in phantom limb sensations?

Under normal circumstances, the dorsal horn of the spinal cord curtails signals, but after an amputation, there is often a loss of this inhibitory control, leading to intensified signals.

How does the somatosensory cortex process sensory signals related to phantom limbs?

The somatosensory cortex processes sensory signals, and the entire body is mapped in this cortex. The cortical map is likely responsible for the feeling of body parts that are no longer there.

What is the cortical homunculus and how does it relate to phantom limb sensations?

The cortical homunculus is a model of the human body with proportions based on the size of each body part's representation in the cortex. It helps explain why sensitive body parts are represented by larger areas and how the brain can still 'feel' a limb that is no longer there.

Can the brain adjust the cortical representation of a body part?

Yes, the amount of cortex devoted to a specific body part can grow or shrink based on how much sensory input the brain receives from that body part.

How does the brain's representation of a body part relate to phantom pain?

An increased representation of a body part in the brain, often due to injury, can lead to heightened sensations and potentially phantom pain.

What is mirror box therapy and how can it help with phantom limb pain?

Mirror box therapy is a technique where a patient places the phantom limb behind a mirror and the intact limb in front, tricking the brain into seeing the phantom, which can help develop range of motion and reduce pain.

How can prosthetics help with phantom limb sensations and pain?

Prosthetics can help patients conceptualize them as extensions of their bodies, allowing for intuitive manipulation and potentially reducing pain, especially when used consistently.

What are some of the unanswered questions about phantom limbs?

We don't know why some amputees escape the pain typically associated with phantom limbs, or why some don't have phantoms at all.

How can the study of phantom limbs provide insight into our everyday perception?

A deeper understanding of phantom limbs can give us insight into how our brains build the world as we perceive it, reminding us that our realities are subjective.

Outlines

00:00

🤚 Phantom Limb Sensations Explained

Phantom limb sensations are a phenomenon where individuals who have lost a limb continue to feel it with vivid detail, including sensations like touch and pain. This suggests that our brains possess a body map that is present from birth. After amputation, the neural pathways that once carried sensory input from the limb are disrupted, leading to changes in signal transmission. Severed nerve endings can become sensitive, transmitting distress signals that are not properly inhibited in the spinal cord, leading to pain. The brain's somatosensory cortex, which maps the body, may also contribute to phantom sensations by maintaining a representation of the missing limb. Over time, this representation can shrink, potentially reducing phantom limb sensations. Treatments for phantom pain include physical therapy, pain management medications, prosthetics, and time, with mirror box therapy being a particularly effective method to reduce pain and develop range of motion by tricking the brain into seeing the phantom limb.

Keywords

💡Phantom Limb

A phantom limb refers to the sensation that an amputated or missing limb is still attached to the body. This phenomenon is central to the video's theme, as it explores the experiences of individuals who can still feel a limb that is no longer physically present. The script mentions that 'the vast majority of people who’ve lost a limb can still feel it,' highlighting the pervasive nature of this sensation.

💡Sensory Neurons

Sensory neurons are specialized nerve cells that transmit information from various parts of the body to the central nervous system. In the context of the video, these neurons are crucial for the discussion of phantom limb sensations, as they are responsible for the sensory input that the brain interprets. The script explains that 'our limbs are full of sensory neurons responsible for everything, from the textures we feel with our fingertips, to our understanding of where our bodies are in space.'

💡Neural Pathways

Neural pathways are the routes through which nerve impulses travel from the periphery of the body to the central nervous system. The video discusses how these pathways are altered after amputation, leading to phantom sensations. It is mentioned that 'neural pathways carry this sensory input through the spinal cord, and up to the brain,' emphasizing their role in the transmission of sensory information.

💡Amputation

Amputation is the surgical removal of a limb or part of a limb. The video focuses on the aftermath of amputation, particularly the changes in sensory perception that lead to phantom limb sensations. The script states that 'the loss of a limb alters the way signals travel at every step of the pathway,' illustrating the direct impact of amputation on the experience of phantom limbs.

💡Dorsal Horn

The dorsal horn is a part of the spinal cord where incoming sensory signals are processed and modulated. The video discusses how, after amputation, there is a loss of inhibitory control in the dorsal horn, leading to intensified sensory signals. The script explains that 'under normal circumstances, these signals would be curtailed in the dorsal horn of the spinal cord,' but after amputation, this control is lost.

💡Somatosensory Cortex

The somatosensory cortex is the area of the brain that processes sensory information related to touch, temperature, pain, and pressure. The video ties this concept to the experience of phantom limbs, as the cortex continues to process sensory signals even when the limb is no longer present. The script describes that 'sensory signals reach the brain, where the somatosensory cortex processes them,' indicating its role in the perception of the body.

💡Cortical Homunculus

The cortical homunculus is a distorted map of the body based on the amount of sensory and motor cortex devoted to each body part. The video uses this concept to explain the representation of body parts in the brain and how this can change, such as in phantom limb sensations. The script mentions that 'the cortical homunculus is a model of the human body, with proportions based on the size of each body part’s representation in the cortex,' highlighting its relevance to the theme of sensory perception.

💡Phantom Pain

Phantom pain is the experience of pain in a limb that has been amputated. The video delves into the reasons behind this painful sensation, which is a common aspect of phantom limb experiences. The script notes that 'the vast majority of them are painful,' suggesting that phantom pain is a significant part of the phantom limb phenomenon.

💡Mirror Box Therapy

Mirror box therapy is a treatment technique used to alleviate phantom limb pain by creating a visual feedback loop that tricks the brain into 'seeing' the phantom limb. The video discusses this therapy as a potential treatment for phantom pain, mentioning that 'a technique called mirror box therapy can be very helpful in developing the range of motion and reducing pain in the phantom limb.'

💡Prosthetics

Prosthetics are artificial limbs or body parts that replace a missing part of the body. The video touches on how prosthetics can influence the experience of phantom limbs and pain. It is noted that 'prosthetics can also create a similar effect,' suggesting that the interaction with prosthetic devices can have therapeutic benefits for individuals with phantom limb sensations.

Highlights

Most amputees can still feel their missing limb in vivid detail.

Phantom limb sensations suggest a body map exists in our brains.

Some people born without a limb can also experience phantom sensations.

Phantom limbs often involve painful sensations, unlike natural limbs.

Sensory neurons in limbs send signals through neural pathways to the brain.

Amputation alters signal transmission at various points in the neural pathway.

Severed nerve endings can become sensitive and transmit distress signals.

After amputation, inhibitory control in the spinal cord's dorsal horn is often lost.

The somatosensory cortex processes sensory signals from the body.

The cortical homunculus represents body parts based on their cortical area.

Cortical representation can change based on sensory input and injury.

Increased cortical representation can lead to phantom pain.

The cortical map is likely responsible for the feeling of absent body parts.

Phantom limb sensations may diminish as cortical representation shrinks over time.

Treatment for phantom pain includes physical therapy, medications, prosthetics, and time.

Mirror box therapy can help reduce phantom limb pain by tricking the brain.

Virtual reality treatments are being developed to enhance mirror box therapy.

Prosthetics can help patients conceptualize them as body extensions, reducing pain.

There are still many unanswered questions about why some amputees don't experience phantom pain.

Understanding phantom limbs can provide insight into how our brains construct our perceived reality.

Phantom limbs remind us that our realities are subjective.

Transcripts

The vast majority of people who’ve lost a limb can still feel it—

not as a memory or vague shape, but in complete lifelike detail.

They can flex their phantom fingers

and sometimes even feel the chafe of a watchband

or the throb of an ingrown toenail.

And astonishingly enough,

occasionally even people born without a limb can feel a phantom.

So what causes phantom limb sensations?

The accuracy of these apparitions

suggests that we have a map of the body in our brains.

And the fact that it’s possible

for someone who’s never had a limb to feel one

implies we are born with at least the beginnings of this map.

But one thing sets the phantoms that appear after amputation

apart from their flesh and blood predecessors:

the vast majority of them are painful.

To fully understand phantom limbs and phantom pain,

we have to consider the entire pathway from limb to brain.

Our limbs are full of sensory neurons responsible for everything

from the textures we feel with our fingertips

to our understanding of where our bodies are in space.

Neural pathways carry this sensory input through the spinal cord

and up to the brain.

Since so much of this path lies outside the limb itself,

most of it remains behind after an amputation.

But the loss of a limb

alters the way signals travel at every step of the pathway.

At the site of an amputation,

severed nerve endings can thicken and become more sensitive,

transmitting distress signals even in response to mild pressure.

Under normal circumstances,

these signals would be curtailed in the dorsal horn of the spinal cord.

For reasons we don’t fully understand, after an amputation,

there is a loss of this inhibitory control in the dorsal horn,

and signals can intensify.

Once they pass through the spinal cord, sensory signals reach the brain.

There, the somatosensory cortex processes them.

The entire body is mapped in this cortex.

Sensitive body parts with many nerve endings,

like the lips and hands,

are represented by the largest areas.

The cortical homunculus is a model of the human body

with proportions based on the size of each body part’s representation in the cortex,

The amount of cortex devoted to a specific body part can grow or shrink

based on how much sensory input the brain receives from that body part.

For example, representation of the left hand is larger in violinists

than in non-violinists.

The brain also increases cortical representation

when a body part is injured

in order to heighten sensations that alert us to danger.

This increased representation can lead to phantom pain.

The cortical map is also most likely responsible

for the feeling of body parts that are no longer there,

because they still have representation in the brain.

Over time, this representation may shrink and the phantom limb may shrink with it.

But phantom limb sensations don’t necessarily disappear on their own.

Treatment for phantom pain usually requires

a combination of physical therapy,

medications for pain management,

prosthetics,

and time.

A technique called mirror box therapy

can be very helpful in developing the range of motion

and reducing pain in the phantom limb.

The patient places the phantom limb into a box behind a mirror

and the intact limb in front of the mirror.

This tricks the brain into seeing the phantom

rather than just feeling it.

Scientists are developing virtual reality treatments

that make the experience of mirror box therapy even more lifelike.

Prosthetics can also create a similar effect—

many patients report pain

primarily when they remove their prosthetics at night.

And phantom limbs may in turn

help patients conceptualize prosthetics as extensions of their bodies

and manipulate them intuitively.

There are still many questions about phantom limbs.

We don’t know why some amputees escape the pain

typically associated with these apparitions,

or why some don’t have phantoms at all.

And further research into phantom limbs

isn’t just applicable to the people who experience them.

A deeper understanding of these apparitions

will give us insight into the work our brains do every day

to build the world as we perceive it.

They’re an important reminder

that the realities we experience are, in fact, subjective.