Rubber Hand Illusion 1

Running head: Rubber Hand Illusion as a Pain Management Therapy

Rubber Hand Illusion as a Pain Management Therapy

Gregory Cordes

General Psychology

PSY5201 – Integrative Project MS in Psychology – Summer 2009

jgcordes@comcast.net

Rubber Hand Illusion 2

Abstract

This paper will discuss the potential of using Rubber Hand

Illusion (RHI) as a pain management therapy. It will address how

RHI is induced - methods to improve the illusion – and other

forms of sensory cross-modalities. In addition, this paper will

describe other effects of RHI – how these integrations are made

in the brain – describe the senses – describe pain theory – brain

structures involved in pain sensation – types of pain – and

current methods of psychologically moderating pain. In the last

part of this paper it will describe the social aspect of pain –

describe the ways people experience pain – the chemical methods

to treat pain – describe how sensory integration modifies and how

disintegration reduces pain.

Rubber Hand Illusion 3

Rubber Hand Illusion as a Pain Management Therapy

What is Rubber Hand Illusion?

Rubber Hand Illusion (RHI) is one way researchers can

demonstrate multisensory integration and crossmodal attention in

the mind, sensory integration of vision, smell, pain, taste,

proprioception, and touch (Spence, 2004). For RHI, it is a

demonstration of the integration of vision and touch, to mis-

integrate proprioception. People can find other integrations, for

example, in vision and sound in Ventriloquist Illusion (VI)

(Bonath, et al., 2007). Once again, vision takes the dominant

role in the illusion. Some of these illusions are remarkably easy

to perform.

For Rubber Hand illusion, a participant sits at a table

(Botvinick and Cohen, 1998). Researchers conceal one of the

participant’s hands behind a blind, while on the opposite side of

the blind investigators position a rubber hand congruent to the

participant’s real hand. The investigator asks the participant to

look at the rubber rand. The researcher then begins to stroke

synchronously both the fake and a real hand with 2 small paint

brushes - in about 14.9s, +/-9s, the participants report sensing

a loss of hand ownership (Ehrsson, Wiech, Weiskopt, Dolan &

Passingham, 2007). Time to full effect varies, Botvinick and Cohn

(1998) report 100% for a stroke time of 10 m for 10 participants

- Durgin, Evans, Dunphy, Klosterman and Simmons (2006) suggest at

Rubber Hand Illusion 4

least 70% for a 2 m stroke time with 220 participants - while

Ijsselsteijn, de Kort and Haans (2005) say 75% with 32

participants during a 7.5 m stroke time. Stroke time may be the

key to induce RHI. There may also be a better way to induce RHI.

Most studies do not divulge much about the exact manner

researchers induce RHI. However, there may be a best approach.

The motor homunculus organizes the premotor cortex into specific

areas were the body receives tactile information. One quarter

divides into the genitals, buttocks, toes, leg, abdomen,

shoulder, and arm (Carlson, 2007). The second quarter divides

into the forearm, palm, fingers and thumb (Carlson, 2007). The

fingers divide, and in order, to the little, ring, middle, index,

and thumb (Nadasdy, n.d.). If people are trying to activate these

areas it might be best to activate in the physical order as they

are stored in the brain, by starting with the little finger and

working across the joints and tips of the fingers. Stimulating

the joints would be a good target because neurons that detect

position terminate in the joints (Eaton, n.d.). Stimulating

finger tips may be best because they are the most tactile

sensitive part of the hand (Eaton, n.d.). In addition, it may be

best to control extraneous activation by performing a “brain

cleansing” procedure, counting down from 1000 by 7 (Fisher,

2004). In addition, taking advantage of VI, by adding a tapping

sound from the brush the practitioner uses on the false hand.

Rubber Hand Illusion 5

Investigators have already found using virtual reality is the

best method to produce RHI (Ijsselsteijn, et al., 2005; Ehrsson,

et al., 2007). Researchers do not need a rubber hand, a

projection of the real hands works better (Ijsselsteijn, et al.,

2005; Ehrsson, et al., 2007). RHI is easy to demonstrate, VI is a

little more complex.

In VI, researchers miss-locate the source of the sound, in

this case a 10 ms tone pip (Bonath, et al., 2007). The

investigators then cue the participants with a light emitting

diode. By flashing the light emitting diode briefly just before

producing the tone, the investigators can misdirect the

participant’s ability to locate where the sound is coming from

(Bonath, et al., 2007). Even more interesting, VI can be long-

lasting (Recanzone, 1998). Participants misidentified the

location of a sound even after cueing the effect stopped. After

cueing participants for 20 to 30 minutes, participants

demonstrated and eight degree error in locating a sound source

(Recanzone, 1998). It is not clearly understood why VI takes

place - however, the dominant theory is priming provokes VI

illusion.

Priming, for lack of a better definition is a hint (Reber

and Reber, 2001). Generally speaking, it is an episode or an

event that start a system functioning (Reber and Reber, 2001).

For VI, the prime is the light emitting diode flashing a split

Rubber Hand Illusion 6

second in the wrong place just before the tone burst. For RHI,

the sight of the synchronously stoking false hand with the real

hand acts as the prime. This is why in the competition among

senses during sensory integration, vision plays the dominant

role. One of the vexing problems with this competition is time.

When people see something, light passes through the lens of

their eyes, across the vitreous humor, striking photoreceptors

that transmit information through bipolar cells to ganglion cells

and then down the optic nerve (Carlson, 2007). It makes a cross

over at the optic chiasm, where left side encoding goes right,

and right side encoding goes left. Visual encoding travels down

the optic nerve to the lateral geniculate nucleus where encoding

divides between optic radiation to the primary visual cortex, and

the superior colliculus terminating at the pulvinar nucleus

(Carlson, 2007). The transmission of information between the

lateral geniculate nucleus and the primary visual cortex is not

unidirectional but, the lateral geniculate nucleus receives

feedback from the primary cortex (Majumder, n.d.). After reaching

the primary visual cortex, encoding splits again between the

dorsal and ventral streams (Carlson, 2007). The ventricle stream

encodes visual information to the inferior temporal cortex where

people store object form. While the dorsal stream encodes

information in the posterior parietal lobe, where people store

object location. Touch works differently.

Rubber Hand Illusion 7

For touch, nerve endings in the fingers, for example, are

stimulated and pass that information down bimodal sensory neurons

through the dorsal root ganglion, up the spinal cord, through the

medulla and midbrain, going through the ventral posterior nucleus

of the thalamus, and terminates in the premotor cortex. Parietal

area 5 then constructs a body schema by incorporating vision,

somesthesis and motor feedback. Touch has a longer trip to make

than vision, but touch gets to the brain first. Evarts (1974) (as

cited in Carlson, 2007, p. 270) found visual stimulus takes 100

ms to get to the brain, while touch reaches the premotor cortex

in only 25 ms. Despite the fact touch gets to the brain first,

vision still acts as the prime. There are several other phenomena

associated with RHI.

The effects of RHI are so profound, in one experiment,

participants experience anxiety when the false hand was

threatened (Ehrsson, et al. 2007). In another experiment,

researchers found participants could feel the touch of light

(Durgin, et al., 2007) - after putting participants into RHI, the

participants pointed to a laser light at the false hand and 70%

reported being able to feel it (Durgin, et al., 2007). Moseley,

et al. (2008) report in one experiment that participant’s hand

temperature dropped by nearly 0.8 degrees C. Moseley, et al.

(2007) also suggest one reason why RHI works is because it slows

tactile processing speed. Hence, visual information gets to the

Rubber Hand Illusion 8

brain before tactile data do and can act as the prime. In the

competition among senses, the brain believes what it sees. This

dominance is so powerful, when people see something painful,

regardless of light conditions - their pupils dilate (Hofle,

Kenntner-Mabiala, Pauli, and Alpers, 2008). Two Swedish

researchers took RHI to a whole other plane of existence.

Petkova and Ehrsson (2008) expand the use of RHI to the

whole body. Using a system of head mounted displays and 2

cameras, they were able to shift body ownership of study

participants to a mannequin, and the researchers can shift

ownership to another person. Males and females can experience

ownership of the other’s gender – and stroking occurs in the

middle of the body, at the stomach. Participants experience

distress when a knife crossed the stomach of a mannequin (Petkova

and Ehrsson, 2008). The researchers do not discuss how the

cameras feed in the head mounted display - a likely scenario

would be to send one signal to the right eye, while sending the

other to the left. This would cause the brain to see and optical

interference (Sternberg, 2006). One image superimposed over the

other. The researchers are investigating the possibilities in

using this approach with individuals suffering from body image

disorders. The authors suggest that they can induce “Body Swap”

(BS) in 70% to 80% of all individuals (Petkova and Ehrsson,

2008). VI, RHI, BS, evidence the mind integrates sensory

Rubber Hand Illusion 9

information. There are several additional pieces of evidence to

suggest sensory integration is the norm rather than the

exception.

Sound Induced Flash Illusion (SIFI) is additional evidence

of sensory integration (Vilentyev, Shimojo, and Shams, 2005). In

this illusion, researchers flash a single dot on a screen for 30

ms. In the controlled condition - the flash follows a single

beep. In the manipulated condition, two beeps follow the flash.

Participants report in the control condition only seeing one

flash, while in the manipulate condition see two. This would

challenge the notion of visual dominance in multi-sensory

perception (Vilentyev, Shimojo, and Shams, 2005). Perhaps, this

is just priming. Human visual senses are limited to conical view

of what is in front of them. Using volume and familiarity, human

auditory senses can approximate the location of a given sound in

three-dimensional space. Humans can approximate the location of

an event better with sound than with sight. One reason the SIFI

works is because the auditory sense acts as a prime for visual

sensory integration. There is additional evidence of multisensory

integration.

Taste and odor are integrated senses (Auvray and Spence,

2007). For example, for most people the perception of odor gives

them a sense of how sweet something is. The very fact humans can

detect sweetness by smell alone is unusual in itself - the

Rubber Hand Illusion 10

olfactory system does not posses the detection organs to make

such a determination (Auvray and Spence, 2007). Taste and touch

have a multisensory integration.

In 2000, Cruz and Green (as cited in Auvray and Spence,

2007) found most people who put an unflavored ice cube by the

side of their tongue are likely to taste a perceivable, yet

fleeting, taste of salt. Cruz and Green’s (as cited in Auvray and

Spence, 2007) research demonstrates a relationship between both

touch and temperature with taste. The taste-temperature illusion

is a curious integration. Perhaps is served early humans with a

danger signal, do not eat ice because they could not, unlike

water, determine whether the frozen liquid is fresh or saltwater.

Hence, a saltwater message is sent to the brain – vision and odor

conspirer against taste in the next integration.

In 1999, Prescott (as cited in Auvray and Spence, 2007)

coined the term “olfactory illusion” for the constant error

humans make when attributing something they taste to their

olfactory sense. Here, both vision and smell localize sensation

in the mouth - vision dominates with help from the olfactory

sense. Odor integrates with vision (Osterbauer et al., 2005).

Osterbauer et al. (2005) research suggests not only does

vision play a part in odor identification, but changing the color

of a flavored beverage will cause individuals to misidentify the

substance because humans associate certain colors with individual

Rubber Hand Illusion 11

flavors. Once again vision takes the dominant role in sensory

integration. Additional evidence for visual dominance in

multisensory integration occurs in the McGurk effect.

The McGurk effect is one of the earliest examples of

multisensory integration (Boersma, 2006). Researchers can

demonstrate McGurk effect by filming an individual speaking “ga,

ga, ga” - then voicing over the “ga, ga, ga” with “da, da, da”.

Individuals viewing the film with their eyes open they hear “da,

da, da”. When they hear the film with their eyes closed they hear

“ba, ba, ba”. Investigators do not completely understand the

reason for this auditory illusion (Boersma, 2006). However, it

does evidence visual dominance in multisensory processing. Some

forms of sensory integration operate faster than a blink of an

eye.

The vestibular ocular reflex is another example of sensory

integration (Stafford and Webb, 2004). The human brain has a form

of steady-cam. If people are suddenly jolted, the inner ear sends

a message to the muscles of the eye, through the brain, to

compensate the angularity of the eye so the brain continues to

receive visual information on a fixed position. This is why when

people are sitting in a car going down a bumpy road they cannot

read. The bumps caused both head and reading material to shift

position - however the vestibular ocular reflex causes their eyes

to shift to the original position of the reading material

Rubber Hand Illusion 12

(Stafford and Webb, 2004). Tactile and audition are sensory

integrated.

Jousmaki and Hari (1998) demonstrate tactile and audition

sensory integration in the parchment skin illusion. Participants

in this study rubbed their hands together back-and-forth at two

cycles per second. Investigators recorded the sound this made. In

a 3 x 3 experiment, the researchers either accentuated or

dampened frequencies over 2 KHz and either increase or decrease

volume by 15 dB. The researchers found by attenuating high

frequency sound, participants rated their own skin as rougher

than in an un-attenuated state - and smoother when investigators

enhanced higher frequencies. On the other hand, lowering the

volume caused participants to report their hands felt rougher,

than in the controlled condition, no manipulation of sound, and

smoother when the volume increased (Jousmaki and Hari, 1998).

There is evidence of an olfactory and tactile sensory

integration.

As far back as 1932, Laird found people believed scented

silk stockings to be a higher quality than an identical unscented

version (as cited in Salah, n.d.). Studies by Demattè, Sanabria,

Sugarman and Spence, (2006) have since confirmed different smells

effects human tactile judgments (as cited in Salah, n.d.). Some

forms of multisensory perception occur as a result of

conditioning.

Rubber Hand Illusion 13

Maeda, Kanai, and Shimojo (2004) demonstrate how sound can

change human perception of motion. Using two transparent gratings

moving in opposite directions on the horizontal, vertical, and

diagonal axis, Maeda et al. (2004) asked participants to judge

whether the bars were moving to, if they were moving in any

direction at all. Participants rated bars moving up, greater than

chance, when the researchers cued a sound where pitch grew from

low frequency to high frequency. In addition, participants rated

moving down, greater than chance, when investigators cued a sound

pitch that changed from high frequency to low frequency (Maeda et

al. 2004). This appears to be learned multisensory integration.

Another learned multisensory integration is the bouncing disks

illusion.

Sanabria, Correa, Lupianez, and Spence (2004) demonstrate

bouncing disks illusion by showing participants two disks

traveling in opposite directions on a horizontal axis. Without

audition, the participants report the disks appear to pass by

each other. However, when audition at the moment of contact, the

participants report seeing the disks bounce off each other

(Sanabria et al., 2004). Again, this is an example of a learned

multisensory integration. Many people have experienced

multisensory disintegrations.

When people have colds sinuses become blocked and the

ability to smell is impaired (Auvray and Spence, 2007).

Rubber Hand Illusion 14

Typically, the taste of things looses their richness. And, some

things can even taste different from normal. The fact that this

disintegration occurs is evidence of the sensory integration

between taste and smell (Auvray and Spence, 2007). With vision

playing a dominant role, it would be interesting to find what

would happen if during this disintegration between taste and

smell if people could somehow look in their own mouths and tell

if taste improves. Vision and touch are closely related sensory

modalities.

In 2006, Johnson, Burton, and Ro (as cited in Johnson, 2008)

demonstrate a relationship between touch and vision in five

experiments. The investigators asked participants to judge touch

sensation in their middle finger with and without a visual cue.

Johnson et al. (as cited in Johnson, 2006) showed in all five

experiments human touch is most sensitive when people see the

point of contact. A summary of sensory integrations follows.

Vision may prove dominant by the number of integrations, but

it does not have primacy, that is to say it is not the sense that

overrules all the other senses in all the integrations. Botvinick

and Cohen (1998) demonstrate a relationship between vision and

touch in the RHI, with vision taking the dominant role. Bonath et

al. (2007) show a relationship between vision and audio, again,

vision taking the dominant role. Petkova and Ehrsson (2008)

produce “Body Swap”, feeling ownership of another body, vision

Rubber Hand Illusion 15

takes the lead again. Osterbauer et al. (2005) demonstrate in

their color wrong beverage test, vision dominates taste. Borsma

(2006) shows in McGurk effect vision plays the dominant role.

Johnson et al. (as cited in Johnson, 2008) demonstrates visual

dominance over touch. In olfactory illusion, Prescott (as cited

in Auvray and Spence, 2007) determines visual and olfactory

dominance over taste. Vilentyev et al. (2005) in SIFI vision will

not always take the lead, with auditory stimulation priming the

brain for a second look. Jousmaki and Hari (1998) show audition

holds sway over tactile sense. Maeda et al. (2004) demonstrate in

changing pitch, audition leads vision. Likewise, Sanabria et al.

(2004) conclude sound over vision in the bouncing disks illusion.

Cruz and Green (as cited in Auvray and Spence, 2007) find

temperature and touch fool taste. Odor alone has dominance over

taste (Auvray and Spence, 2007). The vestibular ocular reflex has

dominance over vision (Stafford and Webb, 2004). Vision

dominates, but it does not have primacy over all the senses.

The primacy of a sense in integration would depend on its

utility to the organism. One reason the vestibular ocular reflex

holds primacy of vision is it is more important. Without a

vestibular sense no organism could get to its feet, assuming it

has feet, or navigate. In terms of primacy, vestibular system

leads. Audition takes second place, in bouncing disks illusion,

SIFI, and changing sound pitch audition leads vision, only in

Rubber Hand Illusion 16

McGurk effect does vision influence audition. Vision, smell, and

taste come in last. The order of the last four it probably the

result of each sense utility, humans can hear what they cannot

see, see what they cannot smell, smell what they cannot taste.

How the brain process multisensory cross modalities comes next.

For vision, information passes through the V1, V2, V4 layers

of the occipital lobe, to the inferior temporal visual cortex and

then the information divides between the amygdala, and

orbitofrontal cortex (Calvert, Spence, and Stein, 2004).

Additional visual information from the striatum continues to both

the amygdala, and orbitofrontal cortex. For touch, information

makes its way to the thalamus VPL, then to the primary

somatosensory cortex, and divides between the orbitofrontal

cortex, and insula. Information travels from the insula to the

amygdala. For olfaction, the brain receives information through

the olfactory bulb, then to the olfactory pyriform cortex. It

then divides between the amygdala, and the orbitofrontal cortex.

For taste, the brain receives messages from taste receptors on

the tongue, through the nucleus of the solitary tract, then

through the thalamus VPMpc nucleus, and to the frontal

operculum/insula. Once again, the brain divides the information

between the amygdala and orbitofrontal cortex. Within this

framework hunger neurons controlled by body weight, stomach

distention, or glucose utilization interact with the

Rubber Hand Illusion 17

orbitofrontal cortex, and with the amygdala through the lateral

hypothalamus. Because all senses transmit information to both the

orbitofrontal cortex and amygdala, researchers believe this is

where multisensory integration takes place (Calvert et al. 2004).

At this point, this paper will turn its attention to defining

what a sense is.

What is a sense?

By dictionary definition it is “the faculty of perceiving by

means of sense organs” (Merriam-Webster, 2009). Given this

definition, humans have more than the five people commonly

believed. For example, humans have tactile senses that are able

to detect pressure, hardness vs. softness, and dullness vs.

sharpness, heat vs. cold, and pain (Myles, Cook, Miller, Rinner,

Robbins, 2000). Human vestibular senses are able to detect where

the body is in space, and detect acceleration, and direction.

Proprioception tells people where a body part is and where

it is going to (Myles et al. 2000). The eye is capable of

detecting hue, tint, and saturation (Howard, 2006). The ear can

detect pitch, volume, timbre, and rhythm. The tongue is capable

of distinguishing between salty, sweet, sour, bitter, and umami -

while human sense of smell can detect mint, floral, ethereal,

musky, resinous, foul, and acrid (Howard, 2006). In a sense, some

micro-integration of sense data must occur or pitch, volume,

timbre, and pitch would not combine into a word. Without micro-

Rubber Hand Illusion 18

integration hue, tint, and saturation would not combine to a

sight. Without micro-integration, salty, sweet, sour and bitter

would not combine into the flavor of a tomato. Sensory

integration must occur on two levels, micro, the combination of

things people can detect on a sub-sensory level, and on the macro

level, the combinations of the subsets people experience. In the

next section, this paper will discuss the theoretical

underpinnings of pain, and how it works in the brain.

What is pain?

In classical theory, people call the convergent model, holds

people experience pain in centers of a neuro-matrix associated

with portions of the cerebral cortex related to touch (Craig,

n.d.). That is to say, people prick their finger - the neurons

transmit the message through convergent neurons, up the spinal

cord, through the thalamus and areas of the cerebral cortex

responsible for touch, the somatosensory cortex, to determine,

something is wrong, where is it wrong, and what needs to occur

next. The message can come in the form of touch, pinch, pressure,

and excessive heat or cold. The convergence model explains things

such as hyperalgesia, pain felt over large areas – referred pain,

pain felt away from the damage tissue – hyperpathia, strong

emotional reactions as a result of pain – and allodynia, abnormal

pain from light cooling or touch. For the last 40 years, this has

been the consensus. Newer theory supported by physiological and

Rubber Hand Illusion 19

anatomical experiments using functional Magnetic Resonance

Imaging (fMRI) and Positron Emission Tomography (PET) in both

human and animal studies suggest a more complex topology (Craig,

n.d.).

One problem with convergence theory is it does not explain

how people can distinguish different kinds of pain, burning,

sharp, cold, or muscle pain (Craig, n.d.). New studies

investigating lamina I neurons in the spinal dorsal horn suggests

these neurons can distinguish between different types of pain.

Another problem with convergence theory is the somatosensory

cortex is not always active during a painful experience. In

addition, there are two structures beyond the sensory touch

cortex that become active during pain. The anterior cingulate

becomes active during a painful experience, this structure is

responsible for motivational behaviors, and specifically how

unpleasant is the pain. Activation in the anterior cingulate

migrates to sub-cortical sites of the amygdala (Craig, n.d.), a

structure associated with emotional memory, fear, anxiety, and

posttraumatic stress disorder (Maren, 2003) – striatum,

responsible for assigning importance to sensory encoding,

ordering encoding for executive function (Anonymous, n.d.) and

cerebellum, a structure responsible for fine motor coordination

(Leiner and Leiner, 1997). During a painful experience, the

parieto-insular becomes active too.

Rubber Hand Illusion 20

The parieto-insular is a structure responsible for sensing

temperature and pain sensations in different parts of the body

(Craig, n.d.). It does this through a controversial substructure

researchers call the VMpo via lamina I neurons that relay

information from the thalamus (Craig, n.d.). Interestingly, the

parieto-insular becomes active even before the actual pain occurs

(Ehrsson, et al. 2007). There are, of course, other views of pain

theory.

In the sensory view of pain, pain provides a precise account

of encounters with ecological stimulus (Trafton, 2005). Pain

elicits a response to the external stimuli. And, the brain

encodes it much like touch and vision. In the sensory view of

pain, the somatosensory system encodes pressure or temperature in

the harmful range. The somatosensory system encodes the intensity

and location of the stimulation. And, injury causes

sensitization. Sensitization can lead to chronic pain. Research

demonstrates damage increases the sensitivity in peripheral

sensory, spinal cord and, brain stem neurons. Other research

suggests analgesics may be one method of preventing sensitization

(Trafton, 2005). Other chemical pain relievers include analgesics

such as local anesthetics, capsaicin, opioids, Non-Steroidal

Anti-Inflammatory Drugs (NSAIDS), and Serotonin-Norepinephrine

Reuptake Inhibitors (SNRIs) (National Institute of Neurological

Disorders and Stroke, 2009). This paper will go into more detail

Rubber Hand Illusion 21

on pain therapies later. The problem with this sensory view of

pain is that it does not easily explained why people with like

injuries have different results (Trafton, 2005). This problem has

led to a new view of pain.

In the new view of pain, pain is one constituent of a well-

being system (Trafton, 2005). The well-being system provides a

judgment of the physiological state of the body, for example,

mood, feelings, stress, and well-being. Pain elicits responses to

body condition, feelings, and well-being. The well-being system

theory suggests pain is encoded in a different fashion than

hearing, touch, and vision. And, pain is part of the autonomic

nervous, endocrine and limbic systems, with pain being one part

of a system. Well-being theory suggests from a neuro-anatomy

point of view, the sensory system detects somatic condition such

as social well-being, sensual touch, local tissue metabolism,

hormonal state, thirst, hunger, visceral sensations, temperature,

and pain. The brain processes these sensations in the limbic

system and in the brain stem. And, the brain perceives these

sensations in the limbic sensory cortex, or insula cortex. The

motor system motivates actions to the right internal conditions.

It receives information from the brainstem, limbic system, and

limbic sensory cortex. The cingulate cortex or limbic motor

cortex controls the response. The insula cortex responds to

thermal pain (Brooks et al., 2002), chronic pain (Kupers, Gybels,

Rubber Hand Illusion 22

and Gjedde, 2000), dynamic exercise (Williamson, McColl, Mathews,

Ginsburg, and Mitchell, 1999), cocaine craving (Kilts et al.,

2001), anger from Damiasio et al., 2000 (as cited in Trafton,

2005) study, and recognition of emotion on faces (Philips et al.,

1997; Winston, Strange, O’Doherty, and Dolan, 2002). The

cingulate cortex becomes active during noxious stimuli, with a

positive correlation to the intensity of pain experienced

(Trafton, 2005). In addition, the cingulate cortex becomes active

in cue-elicited cravings for drugs. A single change in one

component of the processing circuitry can cause over reactions to

both pain and drug abuse (Shaw-Lutchman et al., 2002). That is to

say, a malfunction to one component of the well-being system can

manifest a malfunction in another component. From a well-being

system point of view, pain can be moderated in a number of ways.

One moderating factor is control (Salomons, Johnstone,

Backonja, and Davidson, 2004). The control does not have to be

real, only perceived. Researchers have found in perceive control

of pain, the insula, anterior cingulate, and secondary

somatosensory cortices, brain structures active during pain

attenuated activity (Salomons, Johnstone, Backonja, and Davidson,

2004). Conditioning plays another part in moderating pain.

In the presence of a solicitous spouse, one that is overly

concerned, participants experienced more intense pain as recorded

in electroencephalogram measurements of activation of the

Rubber Hand Illusion 23

cingulate (Flor et al., 2003, as cited in Trafton, 2005). The

cingulate becomes active during painful experiences.

Interestingly, participants experience more intense pain to

electrical stimulus to the back, but not the finger (Flor et al.,

2003, as cited in Trafton, 2005). Other pain moderating factors

included attention shifting (Bantick et al., 2002).

Bantick, et al. (2002) found through Magnetic Resonance

Imaging (MRI) shifting attention away from the site of pain

actually reduced it. The investigators first asked participants

to rate thermal pain on a scale of one to 10 while at the same

time measured brain activity in the insula, mid-cingulate,

hippocampus, and thalamus, areas of the brain active during pain

sensation. The results showed, in both self reporting and MRI

measurements participants experienced less pain while performing

a Stoop counting task, than paying attention to the noxious

stimuli. Investigators also found increased activation of the

orbitofrontal cortex (Bantick et al., 2002; Tracy et al., 2002).

Expectation plays a part in a pain experience.

Wagner et al. (2004) demonstrate with a placebo, humans will

experience less pain if they expect to experience less pain. The

researchers told participants and analgesic cream would lessen

their pain during a shock to their wrist. In two fMRI studies,

the investigators found reduced activity in the thalamus,

anterior cingulate cortex, and the insula during the

Rubber Hand Illusion 24

manipulation. In addition, the researchers found activity just

before the noxious stimuli in the prefrontal area (Wagner et al.,

2004). This paper will address placebo effect later in the work.

Like pain, cigarette cravings have a similar effect in the brain

(Brody et al., 2002).

Brody et al. (2002) using fluorine 18-fluoroeoxyglucose

Positron Emission Tomography (ffPET) found that when cued with an

image of a person handling a cigarette, participants cravings

activated the orbitofrontal cortex, anterior insula bilaterally,

and the dorsolateral prefrontal cortex. In addition, the

investigators unexpectedly found there is also activity in the

right sensorimotor cortex (Brody et al., 2002). Interestingly,

one need not experience physical pain to experience physical pain

in the brain.

Empathy is a form of physical pain in the brain (Singer, et

al., 2004; Morrison, Peelen, and Downing, 2007). With the use of

fMRI, researchers have found upon seeing pain in a loved one,

people actually experience pain in the brain. The pain matrix

activates in the bilateral anterior insula, rostral anterior

cingulate, cerebellum, brain stem, sensori-motor cortex,

posterior insula/secondary somatosensory cortex, and the caudal

anterior cingulate cortex (Singer, et al., 2004). Females are

more subject to this effect than males (Singer, et al., 2004),

probably because females process emotion 13 times faster than

Rubber Hand Illusion 25

males (Pease and Pease, 1998). While activation of these regions

is not as profound as the real thing, people still nonetheless,

“feel your pain”. In the next section, the paper will discuss the

types of pain individuals’ experience.

How do people experience pain?

People experience pain in scores of different ways, however

– investigators can divide pain into two categories, acute and

chronic (NINDS, 2009). In chronic pain, an individual experiences

persistent pain, that resists most medical treatments, where

psychological and environmental factors can make it worse, and

represent the disease. On the other hand, in acute pain, an

individual experiences time limited pain, that usually be treated

and diagnosed, and usually is the result of inflammation, injury,

or disease (NINDS, 2009). The spectrum of pain is wide.

Individuals can suffer from arachnoiditis, an inflammation

of the membranes sheathing the spinal cord and brain – arthritis,

osteoarthritis, ankylosing spondylitis, rheumatoid arthritis,

bursitis, and tendonitis people characterize as joint

inflammation (NINDS, 2009). In addition, people can include back

pain, spondyloisthesis, radiculopathy, characterized by pressure

on the spinal cord – burn pain – cancer pain, associated with the

disease itself, not the treatment – headaches, migraines, cluster

and tension headaches. There is also head and facial pain –

muscle, fibromyalgia, polymyositis, inclusion, body myositis, and

Rubber Hand Illusion 26

dermatomyositis – myofascial pain syndromes where trigger points

in muscles cause pain, this includes fibromyalgia. In addition,

neuro-pathic pain including diabetic neuropathy, reflex

sympathetic dystrophy syndrome, phantom limb, post-amputation

pain, and central pain syndrome a result of trauma – repetitive

stress injuries may include writer’s cramp, carpal tunnel

syndrome, and tendonitis. Other forms of pain include sciatica –

skin disorders such as shingles, herpes, cysts and tumors, and

neurofibromatosis – sports injuries that can range from sprains

to traumatic brain injuries – and spinal stenosis, a narrowing of

the sheath surrounding the spinal cord. In addition surgical pain

– temporomandibular disorder, jaw pain – head traumas – and

vascular diseases, include vasculitis, a blood vessel

inflammation disorder (NINDS, 2009). In the next section, this

paper will discuss the current methodologies people use to treat

pain.

How do people treat pain?

People treat pain using a variety of chemical and non-

chemical techniques (NINDS, 2009). Among the non-chemical

techniques people can include acupuncture - biofeedback –

chiropractic - cognitive-behavioral therapy, more of a relaxation

and coping strategy – counseling, again learning coping

strategies and showing patients what physiological changes pain

can cause – electrical stimulation including tiny electrical

Rubber Hand Illusion 27

pulses - peripheral nerve, spinal cord, and intracerebral

stimulation or deep brain. Other non-chemical pain management

therapies include exercise – hypnosis – low-power lasers –

magnets, though controversial - rehabilitation and physical

therapy – R. I. S. E, Rest, Ice, Compression, and Elevation, and

surgery including, discectomy, microdiscectomy, laminectomy,

spinal fusion, rhizotomy, cordotomy and dorsal root zone

operation (NINDS, 2009). In addition, healing touch is another

non-chemical method (Healing Touch International, n.d.) as well

as massage therapy (Milivojevic, n.d.).

Chemical treatments for pain consist of a cornucopia of

elixirs including acetaminophen, anticonvulsants,

antidepressants, anti-migraine, aspirin, capsaicin,

chemonucleolysis, COX-2 inhibitors, ibuprofen, and nerve blocks

including Novocain, NSAIDS, opioids, and placebos (NINDS, 2009).

Placebos are perhaps the most interesting chemical pain relievers

- people do not know in many cases why they work. One theory is

expectancy - patients believe they will work, so they work.

Another alternate theory is placebos stimulate the brain’s

natural analgesics. Yet another theory suggests placebos reduce

anxiety, thus creating less of a pain experience (NINDS, 2009).

Another group of pain killers are essential oils. One such oil is

oil of clove dentists use to relieve tooth pain, although people

do not understand why it works (M. Weisfeld, personal

Rubber Hand Illusion 28

communication, 2006). In the next section, this paper will

discuss the theoretical underpinnings of using RHI as a pain

management therapy.

Discussion

The establishment of RHI as a pain management therapy would

be contingent on whether pain is an integrated sensation. The

answer for this is sometimes. Integration takes place in the

orbital-frontal cortex (Calvert, Spence, and Stein, 2004). In

Brody et al. (2002) and Bantick’s et al. (2002) examination of

pain, there was activity in the orbital-frontal cortex. Likewise,

Jantsch, Kemppainen, Ringler, Handwerker, and Forster (2005)

found similar activity in the orbital-frontal cortex in a tooth

pain study. However, Wagner et al. (2004) and Salomons, et al.

(2004) found no activation in the orbital-frontal cortex. The

integration of pain with the other senses must be contingent on

some yet unknown catalyst. From a multisensory integration point

of view, pain may appear in one of three states of sensory

integration.

These states would include sensory integration, mis-

integration, and disintegration. In addition, these three states

may work concurrently, the evidence this paper will give will

come from three groups. The first group will be sensory

integration.

Rubber Hand Illusion 29

For most people, sensory integration comes normally, hue,

tint, saturation combine to form the micro-integration of sight.

Pitch, rhythm, volume, and timbre combine to form the micro-

integration of sound. People’s reaction to pain is normal - it

does not include the miniscule reactions of photons falling onto

hands, nor do people react to moderate sounds, small prods or

pinches. When however, brain tissue is damaged the effect is

different.

Stroke victims with injury to the pain regulatory structures

of the brain may suffer from Central Pain (CP) or Central Post-

Stroke Pain (CPSP) (Leijon and Johnasson, 1989; Craig, Reiman,

Evans, and Bushnell, 1996). Researchers identify CP as a

hypersensitivity to cold and heat - these victims have unusual

reactions to pin-pricks. Investigators think damage to the pain

regulating structures of the brain may be the reason of this

hypersensitivity (Leijon and Johnasson, 1989; Craig, Reiman,

Evans, and Bushnell, 1996). In these individuals, sensory

integration mis-integrates. Human beings are born incomplete -

this is true for sensory integration too.

Premature born children have an unusually high pain

tolerance because they lack sensory integration (Milner, 2002).

Children with sensory integration problems have a higher than

normal tolerance for pain (Cantu, 2002). For all purposes, the

case for RHI as a pain management therapy rest with its sensory

Rubber Hand Illusion 30

disintegration characteristic, where there is a denial of

proprioception, and vision. There are no guarantees to this

suggestion.

Sensory mis-integration and disintegration may occur

simultaneously. During RHI, people report they cannot feel their

hand, or locate it. They can feel their hand, just not where it

is. On the other hand, Durgin et al. (2006) report during RHI,

individuals can feel light touch. This would evidence at least

some mis-integration is taking place. Botvinick and Cohen (1998)

report RHI is fragmentary, so some disintegration is occurring.

The applications for RHI as a pain management therapy are

numerous.

For example, health care providers could apply RHI as a pain

management therapy in intravenous injection, glucose stick

testing for diabetes, splinter removal, venipuncture (blood

extraction), tuberculosis testing, suture and bandage removal,

and blistered irrigation. In a home, people could use RHI for

temporary pain relief from frostbite, minor scratches and wounds.

It is difficult to predict the effectiveness of RHI as a pain

management therapy.

At best, researchers can only estimate the effectiveness of

RHI as a pain management therapy. First, it is necessary to see

how many people succumb to RHI. Botvinick and Cohn (1998) report

100%, Durgin have et al. (2006) report 70%, while Ijsselsteijn et

Rubber Hand Illusion 31

al. (2005) report 75%. As stated earlier, in order for RHI to

disintegrate pain, pain integration must occur in the orbital-

frontal cortex. This has occurred in only three and five pain

experiments. The best estimate would be a range. At best, RHI as

a pain management therapy would work 60% of the time, Botvinick

and Cohn’s (1998) 100% induced participants times 0.6 for the

three out of five studies. At worst, RHI as a pain management

therapy would be 42% for the Durgin et al. (2006) 70% induced

participants times 0.6 for the three out of five studies. Tracy

et al. (2002) only looked at the periaqueductal gray in the brain

stem - they would not have seen activation of the orbital-frontal

cortex. Even these numbers are rough because people can expect

some placebo effect even in cases where practitioners cannot

induce RHI or, where activation of the orbital-frontal cortex

does not occur. Wagner et al. (2004) suggests even placebo effect

will reduce pain. There is also some support for Moseley’s (2007)

claim that sensory disintegrating effects of RHI slow processing

speed.

In a study conducted by Hecht, Reiner, and Halevy (2005),

investigators asked participants to respond as quickly as

possible when provided with a visual, audio, haptic, visual-

auditory, haptic-auditory, haptic-visual, or haptic-visual-

auditory. Uni-modal responses were the slowest, at 430 ms for

visual, 330 ms for auditory, and 318 ms for haptic. Bi-modal

Rubber Hand Illusion 32

responses were a bit faster with visual-auditory at 302 ms,

haptic-visual at 294 ms, and haptic-auditory at 272 ms. Finally,

participants perform the fastest in the haptic-visual-auditory

condition at 263 ms (Hecht, Reiner, and Halevy (2005). The more

senses integrate, the faster processing speed.

Rubber Hand Illusion 33

Conclusion

Perhaps the strongest support for using RHI as a pain

management therapy comes from Bantick et al. (2002), shifting

awareness from the site of pain (Tracy et al., 2002). Loss of

hand ownership as a result of sensory disintegration during RHI

is the ultimate form of loosing awareness. Even in cases where

RHI is not achieved, people can expect some pain relief from the

placebo effects the illusion provides (NINDS, 2009). There is

additional support for RHI as a pain management therapy in

Johnson et al. (as cited in Johnson, 2008). Human ability to

detect touch diminishes when people cannot see what is touching

as Johnson et al. (as cited in Johnson, 2008). There is

additional support for RHI as a pain management therapy in

Milner’s (2002) description of the high tolerance for pain in

poor sensory integration premature babies, and in Cantu’s (2002)

description of high tolerance for pain in poor sensory

integration children.

Rubber Hand Illusion 34

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http://people.hnl.bcm.tmc.edu/jli/reference/143.pdf