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The analgesic effect of crossing the arms


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The ability to determine precisely the location of sensory stimuli is fundamental to how we interact with the world; indeed, to our survival. Crossing the hands over the body midline impairs this ability to localize tactile stimuli. We hypothesized that crossing the arms would modulate the intensity of pain evoked by noxious stimulation of the hand. In two separate experiments, we show (1) that the intensity of both laser-evoked painful sensations and electrically-evoked nonpainful sensations were decreased when the arms were crossed over the midline, and (2) that these effects were associated with changes in the multimodal cortical processing of somatosensory information. Critically, there was no change in the somatosensory-specific cortical processing of somatosensory information. Besides studies showing relief of phantom limb pain using mirrors, this is the first evidence that impeding the processes by which the brain localises a noxious stimulus can reduce pain, and that this effect reflects modulation of multimodal neural activities. By showing that the neural mechanisms by which pain emerges from nociception represent a possible target for analgesia, we raise the possibility of novel approaches to the treatment of painful clinical conditions. Crossing the arms over the midline impairs multimodal processing of somatosensory stimuli and induces significant analgesia to noxious hand stimulation.
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The analgesic effect of crossing the arms
A. Gallace
, D.M.E. Torta
, G.L. Moseley
, G.D. Iannetti
Department of Psychology, University of Milano-Bicocca, Italy
Department of Neuroscience, Physiology and Pharmacology, University College London, UK
Department of Psychology, University of Turin, Italy
The Sansom Institute for Health Research, University of South Australia, Adelaide, and Neuroscience Research Australia, Sydney, Australia
Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article.
article info
Article history:
Received 24 May 2010
Received in revised form 22 December 2010
Accepted 10 February 2011
Body posture
Laser stimulation
Event-related potentials (ERPs)
The ability to determine precisely the location of sensory stimuli is fundamental to how we interact with
the world; indeed, to our survival. Crossing the hands over the body midline impairs this ability to local-
ize tactile stimuli. We hypothesized that crossing the arms would modulate the intensity of pain evoked
by noxious stimulation of the hand. In two separate experiments, we show (1) that the intensity of both
laser-evoked painful sensations and electrically-evoked nonpainful sensations were decreased when the
arms were crossed over the midline, and (2) that these effects were associated with changes in the mul-
timodal cortical processing of somatosensory information. Critically, there was no change in the somato-
sensory-specific cortical processing of somatosensory information. Besides studies showing relief of
phantom limb pain using mirrors, this is the first evidence that impeding the processes by which the
brain localises a noxious stimulus can reduce pain, and that this effect reflects modulation of multimodal
neural activities. By showing that the neural mechanisms by which pain emerges from nociception rep-
resent a possible target for analgesia, we raise the possibility of novel approaches to the treatment of
painful clinical conditions.
Ó2011 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.
1. Introduction
Pain reduces tissue damage by motivating escape [12]. In order to
be fully effective for survival, the ability to localize where a noxious
stimulus occurs must be as accurate as possible [54]. Furthermore,
the processing of the spatial information of a sensory input is one
of the important requisites for it reaching awareness, as impeding
the processing of a stimulus’ location often impedes also the percep-
tion of that stimulus [17,18]. This raises the possibility that disrupt-
ing the processes by which the location of a sensory stimulus is
determined will reduce the perceived intensity of that stimulus.
Remarkably, disrupting the very processes by which nociceptive
input emerges into awareness [27] by acting upon its correct spa-
tial localization has not, until now, been targeted as a method of
reducing pain in healthy volunteers, although the mislocalization
of noxious stimuli by a mirror has been shown to result in reduc-
tion of pain in patients with phantom limb [47]. In contrast, there
have been successful attempts to impede awareness of nociceptive
stimuli by acting upon a person’s state of consciousness or atten-
tion [26,35].
The ability to localise tactile inputs is impaired when hands are
crossed over the body midline [1]. For example, when 2 sequential
stimuli are presented, one on each hand, crossing the hands over
the body midline reduces our ability to determine which hand
was stimulated first [15,53]. This ‘‘crossed-hands deficit’’ is
thought to occur because of a mismatch between the location of
the stimulus within an anatomical (or somatotopical) frame of ref-
erence and the location of the stimulus within a space-based frame
of reference [4,16,53]. Indeed, to localize correctly sensory inputs
in the environment, most of the somatosensory experience must
be referred to spatial locations defined according to nonsomato-
topical frames of reference [20,42,45]. It is thought that integration
of information between these 2 frames of reference probably oc-
curs in multimodal brain areas, that is, areas responding to stimuli
of different sensory modalities [2].
So far, crossed-hands studies have not explored the intensity of
perception or the neural activity elicited by somatosensory stimuli
delivered to the hands. Given that (1) crossing the hands over the
body midline impairs the ability to localise tactile stimuli [1]; (2)
localization of tactile stimuli is an important requisite for awareness
(eg, [18]); and (3) multimodal brain areas (eg, associational and lim-
bic areas that respond to stimuli belonging to different sensory
modalities [2,32]) have been hypothesized to play a more important
role in awareness of both tactile [17] and noxious [27] stimuli than
somatosensory-specific brain areas do, we hypothesized that
0304-3959/$36.00 Ó2011 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.
Corresponding author. Address: Department of Neuroscience, Physiology and
Pharmacology, University College London, Medical Sciences Building, Gower Street,
London WC1E 6BT, UK. Tel.: +44 (0) 20 7679 3759.
E-mail address: (G.D. Iannetti).
152 (2011) 1418–1423
crossing the arms would impede multimodal processing of somato-
sensory stimuli delivered to the hands, and thereby decrease the
intensity of both painful and tactile sensations. As multimodal pro-
cessing of somatosensory stimuli is reflected in the late components
of the event-related potentials (ERPs) elicited by somatosensory
stimuli [40], we would expect a stronger modulation of late rather
than early ERP components when the hands are crossed over the
To test these 2 hypotheses, we investigated the intensity of the
sensations (Experiment 1) and the brain activity (Experiment 2)
evoked by nonnociceptive electrical stimuli and nociceptive laser
stimuli delivered to the hands, while the subject’s arms were either
crossed or not crossed over the body midline.
2. Material and methods
2.1. Participants
Eight right-handed healthy subjects (4 women, mean age
28 ± 4.7 years) took part in Experiment 1. Twelve right-handed
healthy subjects (6 women, mean age 31 ± 10.6 years) took part in
Experiment 2. All participants gave their written informed consent.
This study conformed to the standards required by the Declaration of
Helsinki and was approved by the institutional ethics committee.
2.2. Procedure
Participants were comfortably seated in a silent, temperature-
controlled room, and wore protective laser-proof goggles. Earplugs
and headphones were also worn in order to remove any possibly
auditory cue arising from the operation of the devices. Two large
wooden screens placed in front of the participants occluded their
view of both their arms and the experimenter. A fixation point was
placed 30 cm in front of, and 30°below their eyes. Before the begin-
ning of the experiments participants were familiarised with the sen-
sory stimulation (5–10 stimuli of each modality). During the
experiment the participants were asked to keep their arms either un-
crossed or crossed over the midline. The distance between the hands
was the same (40 cm) in the 2 conditions. Crossed and uncrossed
blocks were run separately (see below for further details).
2.2.1. Nonnociceptive somatosensory stimuli
Nonnociceptive somatosensory stimuli consisted of constant
current square-wave pulses (1-ms duration; DS7A, Digitimer, Hert-
fordshire, UK) delivered through 2 electrodes (0.5 cm diameter,
2 cm interelectrode distance) placed at the wrist, over the superfi-
cial radial nerve. Stimulus intensity was adjusted to elicit a clear,
nonpainful paresthesia. Electrical stimuli were always delivered
at an intensity that was above the threshold of Abfibres (which
convey nonnociceptive tactile information) but below the thresh-
old of nociceptive Adand C fibres [9]. In all experiments, electrical
stimuli were never reported as painful.
2.2.2. Nociceptive somatosensory stimuli
Nociceptive somatosensory stimuli consisted of 4-ms pulses of
radiant heat generated by an infrared neodymium yttrium alumin-
ium perovskite (Nd:YAP) laser (wavelength 1.34
m, El.En. Group,
Florence, Italy). Beam diameter at target site was 8 mm. Laser
stimuli were delivered to the sensory territory of the superficial
radial nerve. Stimulus energy was initially adjusted to elicit a clear
painful pinprick sensation, related to the selective activation of Ad
skin nociceptors, thus solving the previously problematic issue of
the co-activation of nonnociceptive afferents [7,10]. To prevent
nociceptor fatigue or sensitization, the laser target was displaced
after each pulse.
Both experiments involved 8 blocks of 30 stimuli each (inter-
stimulus interval randomised between 8 and 12 seconds). Fifteen
stimuli were delivered to each hand in pseudorandom counterbal-
anced order. The maximum number of consecutive stimuli deliv-
ered to the same hand was 3. Both stimulus modality
(nonnociceptive and nociceptive) and hand position (crossed or
uncrossed) were the same within each block. There were 2 blocks
each of ‘‘nonnociceptive crossed,’’ ‘‘nonnociceptive uncrossed,’’
‘‘nociceptive crossed,’’ and ‘‘nociceptive uncrossed.’’ The order of
blocks was balanced across participants.
2.2.3. Experiment 1
In Experiment 1, 3 energies of both nonnoxious and noxious stim-
ulations were determined using two, 0–100 numerical rating scales,
one for the sensation elicited by laser stimuli and one for the sensa-
tion elicited by electrical stimuli. The anchors of the scale used to
rate the intensity of perception elicited by laser stimuli were ‘‘no pin-
prick sensation’’ (0) and ‘‘the strongest pinprick sensation imagin-
able’’ (100). When rating laser stimuli, participants were explicitly
instructed to rate 0 in response to a nonpricking (eg, nonpainful
warm) sensation. The anchors of the scale used to rate the intensity
of perception elicited by electrical stimuli were ‘‘no electrical sensa-
tion’’ (0) and ‘‘the strongest electrical sensation imaginable’’ (100).
‘‘Low,’’ ‘‘medium,’’ and ‘‘high’’ energies, corresponding to ratings of
30, 50, and 70, were 4.1 ± 1.7 mA, 6.8 ± 2.3 mA, and 10.2 ± 3.4 mA
for electrical and 2 J, 2.5 J, and 3 J for laser stimulation, respectively.
At these energies, Nd: YAP laser pulses consistently elicit painful
sensations (eg, [21]). Ten stimuli of each energy were delivered in
pseudorandom counterbalanced order. The maximum number of
consecutive stimuli of the same energy was 3. Participants rated
the perceived intensity of each stimulus.
2.2.4. Experiment 2
In Experiment 2, one stimulus energy (11.8 ± 4.0 mA for electri-
cal and 3.0 ± 0.5 J for laser) was used. The electroencephalogram
was recorded using 21 scalp electrodes placed according to the
International 10-20 system. The nose was used as common refer-
ence. Signals were amplified and digitized (sampling rate
1024 Hz; resolution = 0.195
V digit
; System Plus, Micromed,
Italy), segmented into 1-second epochs (200 to +800 ms relative
to stimulus onset) and band-pass filtered (1–30 Hz). After baseline
correction (reference interval 200 to 0 ms), artefacts due to eye
blinks or movements were subtracted using a validated method
[23]. Epochs exceeding ± 100
V amplitude (ie, likely to be con-
taminated by artefact) were rejected. They were 0.8 ± 1.6% of the
total number of epochs. Separate average ERP waveforms time-
locked to stimulus onset were computed for each participant,
according to stimulus modality (nonnociceptive or nociceptive)
and hand position (crossed or uncrossed). Baseline-to-peak ampli-
tude of the N1 wave, which represents an early stage of sensory
processing and reflects the somatosensory-specific afferent input
and its somatotopical arrangement, and peak-to-peak amplitude
of the N2-P2 wave, which represents a later stage of processing
and mostly reflects multimodal neural activities [27,40,50], were
measured. The labels N1 and N2-P2 for the ERPs elicited by both
nonnociceptive and nociceptive stimuli were chosen according to
Treede et al [49]. Analyses were conducted using Letswave [39]
and Matlab (MathWorks, Natick, MA, USA).
3. Results
3.1. Experiment 1
For each of the 3 energies used, laser stimuli elicited a clear pin-
prick pain in all participants, related to the activation of Adfibres
A. Gallace et al. / PAIN
152 (2011) 1418–1423 1419
[7]. Ratings of perceived intensity are reported in Table 1. A 3-way
analysis of variance (‘‘stimulus modality’’ [nonnociceptive or noci-
ceptive] ‘‘arm position’’ [crossed or uncrossed] ‘‘stimulus en-
ergy’’ [low, medium, or high]) revealed that crossing the arms
reduced the intensity of the sensation evoked by the stimuli,
regardless of their sensory modality and of the energy of the
applied stimulus (main effect of ‘‘arm position’’: F(1, 6) = 7.54,
P= 0.03; ‘‘stimulus modality’’ ‘‘arm position’’ interaction:
F(1, 6) = 0.55, P= 0.48; ‘‘stimulus energy’’ ‘‘arm position’’ interac-
tion: F(1, 6) = 0.07, P= 0.91). That is, crossing the arms decreased
the intensity of the sensations elicited by both nonnoxious and
noxious stimuli (Fig. 1).
3.2. Experiment 2
Amplitudes of ERPs are reported in Table 2. A 2-way analysis of
variance (‘‘stimulus modality’’ [nonnociceptive or nociceptive]
‘‘arm position’’ [crossed or uncrossed]) revealed that crossing the
arms over the midline reduced the amplitude of the N2-P2 wave,
regardless of stimulus modality (main effect of ‘‘arm position’’:
F(1, 11) = 9.27, P= 0.01; ‘‘stimulus modality’’ ‘‘arm position’’
interaction: F(1, 11) = 0.04, P= 0.81). In contrast, crossing the arms
did not reduce the amplitude of the N1 wave for either stimulus
modality (main effect of ‘‘arm position’’: F(1, 11) = 1.43, P= 0.26;
‘‘stimulus modality’’ ‘‘arm position’’ interaction: F(1, 11) = 0.16,
P= 0.68), which shows no effect of crossing the arms on somato-
sensory-specific processing (Fig. 2).
4. Discussion
We hypothesized that crossing the arms would impede multi-
modal processing of somatosensory stimuli delivered to the hands,
and thereby decrease pain and touch. Our results clearly uphold
this hypothesis – crossing the arms reduced the perceived inten-
sity of both laser-evoked painful sensations and electrically evoked
nonpainful sensations, as evidenced by the behavioural data
(Experiment 1), and selectively disrupted multimodal processing
of both nonnociceptive and nociceptive somatosensory stimuli,
as evidenced by the decreased amplitude of the N2-P2 wave
(Experiment 2). The clear dissociation between the absence of N1
wave modulation and the presence of N2-P2 wave modulation
indicates a clear effect of crossing the arms on multimodal, but
not somatosensory-specific, neural processing.
One possible explanation for this effect relies on the cognitive
costs associated with realigning neural representations based on
different spatial frames of reference. When we cross our hands,
the conflict between the sensory inputs represented in different
frames of reference requires the brain to realign somatosensory
coordinates to spatial coordinates, which has a cost in terms of pro-
cessing resources [53]. The modulation of the neural components
reflected in the N2-P2 peaks is likely to represent the neural corre-
late of this cost, while the reduced intensity of the sensations elic-
ited by both nonnoxious and noxious stimuli represents its
behavioural counterpart.
A second possible explanation is related to the fact that, when
the arms are held in an uncommon posture (ie, when they are
crossed), the relevance of the stimuli delivered on the hands might
be reduced. Indeed, it has been repeatedly reported that the atten-
tional context in which the eliciting stimulus is presented alters
the magnitude of the N2 and P2 peaks of somatosensory ERPs, even
if the intensity of the afferent input is constant (eg, [21,27–29]).
It has been suggested that nonnociceptive somatosensory infor-
mation is initially processed in a somatotopic frame of reference,
and needs to be later transformed into a more abstract frame of
reference to become available for conscious processing ([24,53];
though see [16]). Thus, the crossed-hand deficit has been so far
interpreted in terms of the process of progressive ‘‘recoding’’ of
sensory information throughout different spatial maps [4].
However, it is well known that the several cortical maps in pri-
mate sensory systems are activated both in series and in parallel,
and that they are heavily interconnected [38]. There is also evi-
dence of parallel processing in the human somatosensory system
(eg, [25,33]). For example, after ischemic injury to one entire pri-
mary somatosensory area, patients can be completely unaware of
tactile stimuli delivered to the contralateral body side, but still able
to point correctly to where they occurred [6,42,51]. This empirical
evidence of a somatosensory equivalent of blindsight [44,52] sug-
gests that spatial information regarding tactile stimuli can be pro-
cessed and integrated with motor commands, without primary
somatosensory cortex involvement, possibly by direct anatomical
connections between the lateral posterior thalamic nuclei and
the posterior parietal cortex [6,18,22,33].
On that basis, an alternative possibility can be suggested: that
tactile stimuli, rather than being sequentially converted from one
frame of reference to another, are always mapped both in a
somatosensory and in a space-based representation, and that this
dual mapping happens before conscious judgments are made.
Obviously, the strength of activation of each map might be modu-
lated by a number of parameters (such as the availability of visual
and proprioceptive information, as well as the immediate
relevance of the task; eg, [16]). For example, seeing the arms might
enhance the neural representation of sensory stimuli in the space-
based map. Thus, the modulation of the perceived intensity of a
stimulus delivered to the hands while they are crossed over the
midline might not be the consequence of the need to remap the in-
put from the somatosensory to the spaced-based map, but of a lack
of correspondence between the ‘‘expected’’ neural activities elic-
ited by the stimulus in these 2 maps.
In everyday life, the right and left hands manipulate objects and
are exposed to somatosensory stimuli that are more often present
on the right or on the left side of space, respectively. For example,
stimuli activating mechanoreceptors on the left hand occur much
more often on the left side of the body midline. Thus, the represen-
tation of the hand in the somatotopic map is often activated to-
gether with the representation of the left side of space in the
space-based map (Fig. 3). Consequently, it is likely that, among
the extensive connections between these 2 maps [17,18], those
between the regions more often receiving a sensory input resulting
in a simultaneous pattern of activity (eg, the left hand area in the
somatosensory map and the left side area of the space-based
map) are likely to display increased synaptic strengths. When our
hands are uncrossed, the match between the 2 frames of reference
makes the processing of sensory stimuli delivered to the hands
Table 1
Experiment 1: behavioural results.
Hands uncrossed Hands crossed
Electrical stimulation
Energy 1 18.4 ± 10 17.2 ± 10
Energy 2 32.8 ± 9 31 ± 9
Energy 3 45.3 ± 13 43.5 ± 12
Laser stimulation
Energy 1 20.3 ± 8 17.8 ± 8
Energy 2 48.2 ± 9 44.6 ± 9
Energy 3 60.6 ± 8 57.7 ± 9
Values are expressed as mean ± SD. Statistical comparisons are reported in the text.
Values represent intensity of perception according to a 0–100 numerical scale,
where 0 represents ‘‘no sensation’’ and 100 ‘‘the strongest electrical sensation
Values represent intensity of perception according to a 0-100 numerical scale,
where 0 represents ‘‘no sensation’’ and 100 ‘‘the strongest pinprick sensation
1420 A. Gallace et al. / PAIN
152 (2011) 1418–1423
highly effective in enhancing the sensory signal due to the privi-
leged synaptic connections between the corresponding areas of
the 2 maps (Fig. 3, left panel). In contrast, when we hold an uncom-
mon body posture, such as crossing the hands over the midline,
these privileged synaptic connections are not engaged (Fig. 3, right
panel). Therefore, although the correct localisation of stimuli in
space is still possible, the enhancement of the sensory signal is im-
peded, which might result in decreased intensity of perception.
Interestingly, it has been recently shown that performance in tem-
poral order judgment tasks, which are commonly used to investi-
gate the reference frames involved in the localisation of
somatosensory inputs (as well as the temporal aspects of our
awareness), is abnormal when the hands are crossed over the mid-
line [53], but only in children older than 5 years [41]. This sug-
gests that, ontogenetically, somatosensory events are referred to
nonsomatotopical frames of references only after the development
of space-based maps. Before the development of those maps, our
ability to localise somatosensory stimuli relies completely on ana-
tomical frames of reference.
The magnitude of early components of the response elicited by
somatosensory stimuli (eg, the N1 wave of laser-evoked
Fig. 1. Behavioural results (Experiment 1). The left panel represents the intensity of the sensations evoked by nonnoxious stimuli (left graph) and noxious stimuli (right
graph), which were delivered to the hands while the arms were either crossed (in blue) or uncrossed (in red). Three energies of both types of somatosensory stimuli were
used. Crossing the arms significantly reduced the intensity of the sensation evoked by the stimuli, regardless of their sensory modality (main effect of ‘‘arm position’’: P= 0.03;
‘‘stimulus modality’’ ‘‘arm position’’ interaction: P= 0.48).
Table 2
Experiment 2: event-related potential (ERP) results.
Hands uncrossed Hands crossed
Electrical stimulation
N1 wave 3.8 ± 4.9 4.5 ± 4.8
N2-P2 wave 34.0 ± 14.5 31.5 ± 13.9
Laser stimulation
N1 wave 4.2 ± 3.6 4.8 ± 2.6
N2-P2 wave 36.7 ± 19.3 33.2 ± 17.5
Values represent peak amplitude in
V (mean ± SD). Statistical comparisons are
reported in the text.
Fig. 2. Electrophysiological results (Experiment 2). (A) Grand-average waveforms showing the N1 and N2-P2 waves of somatosensory-evoked potentials elicited by
nonnociceptive electrical stimuli (SEPs, left panel) and nociceptive laser stimuli (LEPs, right panel) delivered to the hand dorsum while arms were crossed (blue waveforms)
and uncrossed (red waveforms). Crossing the arms significantly reduced the peak amplitude of the N2-P2 wave, regardless of stimulus modality (main effect of ‘‘arm
position’’: P= 0.01; ‘‘arm position’’ ‘‘stimulus modality’’ interaction: P= 0.81). In contrast, crossing the arms did not reduce the peak amplitude of the N1 wave for either
stimulus modality (main effect of ‘‘arm position’’: P= 0.26, ‘‘arm position’’ ‘‘stimulus modality’’ interaction: P= 0.68). The clear dissociation between the absence of N1
wave modulation and the presence of a strong N2-P2 wave modulation indicates that the analgesic effect imparted by crossing the arms involves multimodal, but not
somatosensory-specific, processing. (B) Group-level scalp distribution of SEPs (top panel) and LEPs (bottom panel) elicited by stimulation of the hand dorsum while the arms
were crossed (top row in each panel) and uncrossed (bottom row in each panel). Scalp maps are displayed at 20-ms intervals, from stimulus onset to 500 ms poststimulus.
A. Gallace et al. / PAIN
152 (2011) 1418–1423 1421
potentials), which better reflects the magnitude of the ascending
somatosensory volley [27], was not affected by crossing the hands.
This excludes the possibility that the change in body posture mod-
ulated the magnitude of the afferent somatosensory input. This
finding is consistent with single-cell recordings in monkeys that
showed that the neural responses in S1 are correlated to the inten-
sity of the applied stimulus but not to its awareness [13]. In hu-
mans, a clear response of primary somatosensory neurons to
tactile stimuli is observed even when the stimuli are below percep-
tual threshold [30]. In contrast, only late components of the
somatosensory-evoked potentials are correlated with stimulus
awareness [27,43,46,48]. Consistent with these observations, the
observed reduction of perceived intensity consequent to crossing
the arms was only reflected in the reduced magnitude of the late
components of the response elicited by somatosensory stimuli
(the N2-P2 wave of laser-evoked potentials), which, despite the
difficulties related to the limited reliability of source analysis of
EEG data and blind source separation approaches [39], have been
suggested to be largely explained by neural activities arising from
multimodal cortical areas [40]. Thus, the selective modulation of
the N2-P2 response when the hands are crossed indicates that
the observed analgesic effect is related to a modulation of the
activity in multimodal cortical areas.
Which multimodal brain areas may be involved in this phenom-
enon? In both human and nonhuman primates, the posterior
parietal cortex is important for the integration of spatial informa-
tion coming from different sensory modalities [2,8,11,19,34].In
particular, the ventral aspect of the intraparietal sulcus, which di-
vides the parietal lobe into the superior and the inferior parietal
lobules [14], contains neurons that encode the information con-
tained in stimuli belonging to different sensory modalities into a
reference frame that can be accessed by all sensory systems [3].
Part of the human intraparietal sulcus has been shown to play a
pivotal role in the multisensory representation of limb position
[5,31]. Thus, this human area homologous to the ventral aspect
of the intraparietal sulcus in nonhuman primates is also likely to
be related to the modulation of both somatosensory perception
(Fig. 1) and the magnitude of multimodal ERP components (Fig. 2).
This is the first evidence that disrupting the processes by which
the brain localises a noxious stimulus reduces the pain evoked by
that stimulus. The magnitude of the effect shown here is too small
to be clinically important, but it reveals for the first time that the
mechanisms by which a sensory event emerges into awareness
can modulate pain. This extends a previous result that perceptual
illusions can modulate pain [37], and raises a new possible expla-
nation for the purported analgesic effect of mirror therapy,
although that mirror analgesia is due to seeing the reflected image
is not established, and other explanations are possible [36]. Finally,
the current results lay the platform for future studies that maxi-
mise conflict between neural representations of a noxious stimulus
according to somatotopic and space-based frames of reference,
possibly resulting in larger and clinically important analgesic ef-
fects. Perhaps, when we get hurt, we should not only ‘‘rub it better’’
but also cross our arms.
Fig. 3. A putative neurocognitive model supporting the presented findings. Tactile, nociceptive, and proprioceptive information arising from, for example, the right hand
(black arrows), reaches the corresponding areas in the somatosensory cortices. When the hands are uncrossed (left panel), these inputs also activate multisensory areas
mapping the right side of the external space, with reference to the body midline. Thus, stimulation of each hand results in a match between somatosensory and space-based
representations (thick, green double arrow). When the hands are crossed (right panel), somatosensory information arising from, for example, the right hand (black arrows),
reaches the corresponding areas in the somatosensory cortices but, critically, also those multisensory areas mapping the left side of the external space. Thus, stimulation of
each hand results in a mismatch between somatosensory and space-based representations (thin, green-red double arrow). Note that the neural connections between spatially
corresponding areas of the somatotopic and space-based representations (eg, the somatotopic representation of the right hand and the representation of the right side of the
external space) are stronger than those between areas of the somatotopic and space-based representations that do not correspond (see main text for an explanation of the
reasons underlying this assumption). The mismatch between somatosensory and space-based representations results in a reduced perceived intensity of the delivered
1422 A. Gallace et al. / PAIN
152 (2011) 1418–1423
Conflict of interest statement
The authors declare no conflict of interest.
A.G. is supported by a MIUR PRIN07 Grant. G.L.M. is supported
by a Senior Research Fellowship from the National Health and
Medical Research Council of Australia. G.D.I. is University Research
Fellow of The Royal Society.
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A. Gallace et al. / PAIN
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... Altogether these studies support the role of multisensory integration as a defensive strategy, since a fast and accurate identification of a noxious stimulus and pain is critical to protect the body from possible threats. To this end, the relationship between nociception and body representation is necessary for a coherent integration of the body and external frame of reference to localize both innocuous and noxious stimuli (Gallace et al., 2011). ...
... Using a RHI protocol, it was shown that noxious stimuli, delivered by an infrared laser pulse on participants' hand following synchronous stimulation of one minute, were reduced in intensity compared with laser pulses delivered after asynchronous stimulation (Fang et al., 2019). The transient change of the representation of the body due to manipulation of visuo-tactile and proprioceptive information may impact the ability to localize the noxious stimuli resulting in analgesic effects, similar to what happens when the hands are crossed over the midline of the body and a mismatch between somatosensory representation and spatial reference occurs (Gallace et al., 2011). However, it is worth noting that there are also some contradictory results showing that during the RHI pain intensity remains unchanged (Mohan et al., 2012). ...
... Following the PPS constraint, multisensory integration enhances both detection and motor responses for stimuli near the body (Noel et al., 2019;Sambo and Forster, 2009). Multisensory integration therefore appears to play a key role in pain modulation, since strategies that manipulate body representation via multisensory integration are able to reduce both nociceptive pain (Fang et al., 2019;Gallace et al., 2011;Romano et al., 2016Romano et al., , 2014Siedlecka et al., 2014) and chronic neuropathic pain (Moseley, 2007;Pamment and Aspell, 2017;Ramachandran et al., 2009;Ramachandran and Rogers-Ramachandran, 1996;Soler et al., 2010). ...
In this review we focus on maladaptive brain reorganization after spinal cord injury (SCI), including the development of neuropathic pain, and its relationship with impairments in body representation and multisensory integration. We will discuss the implications of altered sensorimotor interactions after SCI with and without neuropathic pain and possible deficits in multisensory integration and body representation. Within this framework we will examine published research findings focused on the use of bodily illusions to manipulate multisensory body representation to induce analgesic effects in heterogeneous chronic pain populations and in SCI-related neuropathic pain. We propose that the development and intensification of neuropathic pain after SCI is partly dependent on brain reorganization associated with dysfunctional multisensory integration processes and distorted body representation. We conclude this review by suggesting future research avenues that may lead to a better understanding of the complex mechanisms underlying the sense of the body after SCI, with a focus on cortical changes.
... La première viendrait de l'apparition d'un conflit entre la douleur ressentie dans leur bras et le fait de voir la représentation visuelle apparaître sur le bras de leur avatar localisé devant eux. Ce conflit aurait ainsi entrainé une perturbation des processus de la localisation de la douleur comme dans l'étude de Gallace [215]. La seconde explication pourrait provenir d'un problème d'interprétation de la question par les participants. ...
... Concernant les stimulations douloureuses, de nombreuses possibilités s'offraient à nous. Les études utilisent en effet différents stimuli douloureux tels que les pressions mécaniques [226], [227], les stimulations thermiques [228], [229] ou électriques [95], [215], [230], [231], la capsaïcine [232], [233] ou encore la douleur ischémique [234], [235]. ...
La douleur est à l'origine de plus de 90% des consultations médicales. La méthode thérapeutique la plus couramment utilisée pour diminuer la douleur est la voie médicamenteuse bien qu'elle ne s'avère pas être sans risque pour les patients puisqu’elle peut entraîner des effets secondaires, des dépendances ou des surdosages. Pour lutter contre ces effets indésirables, de nouvelles thérapies non invasives émergent telle que la réalité virtuelle. Afin d’approfondir cette approche, nous avons étudié au cours de cette thèse les effets d'une représentation visuelle d'une stimulation tactile sur les seuils douloureux et les niveaux d'incarnation chez l'Homme. Pour cela, nous avons modulé différentes variables d’une représentation visuelle, en réalité virtuelle et avons évalué les niveaux d'incarnation des participants dans leur avatar. De plus, nous avons évalué leur douleur objective et subjective lorsqu'une stimulation électrique était délivrée au niveau de leur avant-bras. Nous avons étudié ces effets lorsque la représentation visuelle était présente ou absente et synchrone ou asynchrone à une stimulation électrique (étude 1) ; lorsqu'elle était grossissante et localisée dans le corps ou hors du corps (étude 2) ; et enfin, lorsque le point de vue était à la première ou à la troisième personne (étude 3). Nos résultats ont montré que la présence d'une représentation visuelle grossissante diminuait la douleur par rapport à une absence de représentation visuelle ou à une présence sans grossissement. De même, lorsque deux représentations visuelles grossissent à deux vitesses différentes, le grossissement le plus important entraîne un effet algésique par rapport à un grossissement plus faible. Enfin, nos résultats ont également montré que le point de vue d'un participant à la troisième personne entraîne un effet analgésique (diminution de la douleur) par rapport à un point de vue à la première personne. En revanche, les autres variables étudiées de la représentation visuelle n’ont eu aucun impact sur les composantes de la douleur. Nos résultats suggèrent donc que la modulation d'une représentation visuelle dans un environnement virtuel est une approche intéressante et pertinente pour lutter contre la douleur chez l'Homme.
... 20 Testpersonen wurden kleinen Schmerzempfindungen ausgesetzt, die durch einen Laserstrahl hervorgerufen wurden. Beim Überkreuzen der Arme über der Mittellinie, ähnlich dem Umarmen, berichteten die Teilnehmer, dass sie weniger Schmerzen empfanden (Gallace et al. 2011). Darüber hinaus kann eine Selbstumarmung das Selbstmitgefühl steigern, was wiederum zu einer Senkung des Cortisolspiegels und einem verbesserten Wohlbefinden führt (Neff o. ...
... Obwohl die entsprechende Hypothese H3 bestätigt wurde, weil mehr als die Hälfte der Testpersonen keine positive Reaktion auf die Selbstumarmung angab, hatten die Studentinnen und ihr Betreuer ein klareres Ergebnis gegen die Selbstumarmung erwartet. Dieses stimmt jedoch mit den Ergebnissen eines von Gallace et al. (2011) durchgeführten, bereits erwähnten Experiments überein, bei dem die Teilnehmer über eine verminderte Schmerzwahrnehmung beim Überkreuzen der Arme über der Brust berichteten. Auch wird eine Selbstumarmung von den Teilnehmern positiver wahrgenommen als die Vorstellung einer Umarmung mit einem Roboter. ...
In der theoretischen Diskussion ist mit einem Artificial Companion eine Reihe an Eigenschaften gemeint, welche fördern sollen, dass Nutzer:innen ein technologisches System als verlässlichen und treuen Gefährten wahrnehmen. Bislang gibt es allerdings keinen Konsens darüber, welche Eigenschaften dafür konkret notwendig sind. Der vorliegende Beitrag nähert sich deshalb der Thematik von einer praktischen Seite, damit Aussagen über die Eigenschaften heutiger Companion-Systeme getroffen werden können – welche in der vorliegenden Arbeit als Artificial Companions der ersten Generation bezeichnet werden. Der Beitrag stellt die Ergebnisse einer deskriptiven Datenanalyse von n = 50 Companion-Robotern vor, die hinsichtlich ihres Aussehens und ihrer kommunikativen Fähigkeit verglichen werden. Es erfolgt ein Vorschlag für eine Companion-Typologie anhand ihrer Einsatzgebiete inklusive Beschreibung der zentralen Aufgaben und Funktionen. Der letzte Teil erläutert zwei zentrale Motive, auf deren Grundlage Artificial Companionships entstehen können.
... Changing arm posture can alter tactile sensations and delay the integration of tactile and proprioceptive cues, impairing performance in different tactile processing tasks (Eimer et al., 2003;Holmes et al., 2006;Matsumoto et al., 2004;Yamamoto & Kitazawa, 2001). For instance, not only the accuracy of judging the temporal order of touches on the two hands decreases when the arms are crossed (Yamamoto & Kitazawa, 2001), but this posture also seems to alter the perception of nociceptive stimuli (Gallace et al., 2011;Sambo et al., 2013). Moreover, Pozeg et al. (2014) showed that crossing the arms can increase the effect of bodily illusions such as the illusory self-touch. ...
The role of arm posture in the Uznadze haptic aftereffect is investigated: two identical test stimuli (i.e., spheres, TS) clenched simultaneously appear haptically different in size after hands have been adapted to two spheres (adapting stimuli, AS) differing in size: the hand adapted to a small AS feels TS bigger than the hand adapted to a big AS. In two experiments, participants evaluated the haptic impressions of two TS after adaptation by finding their match on a visual scale. In Experiment 1, all tasks were carried out with arms either uncrossed or crossed. In Experiment 2, only the matching task was performed with arms either uncrossed or crossed while adaptation was conducted by continuously changing arm posture from uncrossed to crossed and vice versa. The illusion occurred irrespectively of arm posture; however, its magnitude was smaller when adaptation was carried out in the classical condition of uncrossed arms. Results are discussed in light of two functional mechanisms: low-level somatotopic mapping (i.e., stimuli conformation) and high-level level factors (i.e., arm posture) that could modulate the haptic perception. (PsycInfo Database Record (c) 2023 APA, all rights reserved).
... In this investigation concerning the spatial content of experiences of pain I focus on acute, cutaneous painful sensations. Similarly, as in case of interoceptive tactile experiences, I am interested whether usual experiences of acute pain have rich, field-like content without significantly relying on spatial information provided by different sensory modalities such as proprioception, touch, or vision (see De Paepe et al., 2014;Gallace et al., 2011, Marotta et al., 2015 for studies showing how proprioceptive information modifies experiences of pain). ...
Full-text available
Philosophical considerations regarding experiential spatial content have focused on exteroceptive sensations presenting external entities, and not on interoceptive experiences that present states of our own body. A notable example is studies on interoceptive touch, in which it is argued that interoceptive tactile experiences have rich spatial content such that tactile sensations are experienced as located in a spatial field. This article investigates whether a similarly rich spatial content can be attributed to experiences of acute, cutaneous pain. It is argued that such experiences of pain do not have field-like content, as they do not present distance relations between painful sensations.
... Ce phénomène a été répliqué chez des patients avec une lombalgie unilatérale et l'on retrouve le même ralentissement au traitement des informations provenant de l'espace douloureux ici postérieur et d'un côté (gauche ou droite) (Moseley et al., 2012).Chez des sujets sains l'on retrouve ainsi une influence de la position des membres dans l'espace sur la perception douloureuse et l'intégration nociceptive. En effet, l'induction d'une douleur par stimulation laser nociceptive est plus faible lorsque les sujets ont les bras croisés que décroisés et cela, s'accompagne de potentiels évoqués de plus faible amplitude(Gallace et al., 2011). De même il a été montré que le réflexe main-clignement (hand-blink reflex en anglais) est modulé par la distance entre les yeux et la main stimulée(Sambo et al., 2011). ...
Full-text available
La douleur est une expérience complexe avec un fort impact sur la vie des patients surtout quand elle devient chronique et invalidante. Actuellement de nouvelles approches thérapeutiques émergent fondées sur une nouvelle compréhension de la douleur.Les patients blessés médullaires (BM) représentent une population chez qui la prise en charge de la douleur est difficile et cela en partie par une faible représentation dans la recherche scientifique. La douleur neuropathique sous-lésionnelle (DNSL) des BM est un modèle intéressant car s’apparente à une douleur de membre fantôme, est encore difficilement comprise, prise en charge et elle, représente un modèle intéressant pour l’étude du lien entre représentation du corps et douleur.Nous avons entrepris deux recherches pour comprendre comment les modifications du système nerveux central peuvent participer à la douleur de ces patients et quel lien peut-il avoir entre douleur et représentation du corps chez eux.Nos résultats ont permis de mettre en avant que les patients présentant des DNSL montrent des signes de plasticité maladaptative au niveau du thalamus, du cortex moteur et du cortex cingulaire ce qui est cohérent avec des altérations de la dite “neuromatrice de la douleur” et une dysrythmie thalamo-corticale déjà décrit dans d’autres pathologies. Les données indiquent aussi une possible neuroplasticité protectrice au niveau du cortex somatosensoriel. Ces changements sont autant de cibles potentielles de pris en charge en rééducation.De même nous avons pu démontrer que les patients BM ont une altération de leur représentation corporelle et que celle-ci est corrélée à l’aspect neuropathique de la douleur.Les données apportées confirment nos hypothèses et ouvrent vers la possibilité d’explorer ces phénomènes plus en avant et de déterminer quels moyens de rééducation peuvent être utiles pour aider les patients avec des DNSL.
... Evidence supporting the interaction between pain and the three mentioned domains of body experience (SoP, SpP, BO) have been found in experimentally-induced pain Gallace et al., 2011;Mancini et al., 2011;Fang et al., 2019) (e.g., distorting the visual appearance of the body). Moreover, a correlation between body and space perception dysfunctions with pain intensity and its duration (Förderreuther et al., 2004;Peltz et al., 2011;Reinersmann et al., 2012), were found in CRPS, thus it would be clinically relevant to clarify if this interaction exists also in MDRDs. ...
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Background: Pain and body perception are essentially two subjective mutually influencing experiences. However, in the field of musculoskeletal disorders and rheumatic diseases we lack of a comprehensive knowledge about the relationship between body perception dysfunctions and pain or disability. We systematically mapped the literature published about the topics of: (a) somatoperception; (b) body ownership; and (c) perception of space, analysing the relationship with pain and disability. The results were organized around the two main topics of the assessment and treatment of perceptual dysfunctions. Methods: This scoping review followed the six-stage methodology suggested by Arksey and O'Malley. Ten electronic databases and grey literature were systematically searched. The PRISMA Extension for Scoping Reviews was used for reporting results. Two reviewers with different background, independently performed study screening and selection, and one author performed data extraction, that was checked by a second reviewer. Results: Thirty-seven studies fulfilled the eligibility criteria. The majority of studies (68%) concerned the assessment methodology, and the remaining 32% investigated the effects of therapeutic interventions. Research designs, methodologies adopted, and settings varied considerably across studies. Evidence of distorted body experience were found mainly for explicit somatoperception, especially in studies adopting self-administered questionnaire and subjective measures, highlighting in some cases the presence of subgroups with different perceptual features. Almost half of the intervention studies (42%) provided therapeutic approaches combining more than one perceptual task, or sensory-motor tasks together with perceptual strategies, thus it was difficult to estimate the relative effectiveness of each single therapeutic component. Viceconti et al. Body Perception in Musculoskeletal Disorders Conclusions: To our knowledge, this is the first attempt to systematically map and summarize this research area in the field of musculoskeletal disorders and rheumatic diseases. Although methodological limitations limit the validity of the evidence obtained, some strategies of assessment tested and therapeutic strategies proposed represent useful starting points for future research. This review highlights preliminary evidence, strengths, and limitations of the literature published about the research questions, identifying key points that remain opened to be addressed, and make suggestions for future research studies. Body representation, as well as pain perception and treatment, can be better understood if an enlarged perspective including body and space perception is considered.
Ağrının birincil önemi vücudu yaralanmalardan korumaktır. Ancak, hayatta kalmak için acıyı algılamamanın daha önemli olduğu bazı durumlar da söz konusudur. Ağrının kendiliğinden bastırılması veya nosisepsiyonun zayıflamasına, endojen antinosiseptif (analjezik) sistem aracılık eder. Anatomik oluşumu, orta beyindeki periakueduktal gri maddeden, beyin sapının noradrenerjik ve serotonerjik çekirdeklerinden, nosiseptörlerden "ağrı" bilgisi alan spinal nöronlara kadar uzanır. Bu sistemin faaliyeti, duygusal ve bilişsel devrelerin kontrolü altındadır. Ağrı, olumlu duyguların uyarılmasıyla hafifletilebilirken, olumsuz duygular hissedilen acıyı artırmaktadır. İlginç şekilde, bir ağrı başka bir acıyı bastırabilme özelliğine de sahiptir. Analjezi; stres, fiziksel egzersiz, orosensöryel uyarılma (tatlı gıda tüketimi), müzik dinleme ve plasebo sonrası, yani ağrıdan kurtulma beklendiğinde duyusal uyarımla indüklenebilir. Ağrının; duyusal, duyuşsal ve bilişsel bileşenleri olduğundan, bu tüm sistemlerin aktivasyonunun belirli şekillerde ağrının bastırılmasına katkıda bulunabileceği ortaya konmuştur.
Umarmungen sind für das Wohlbefinden von Menschen jeden Alters wichtig. Nicht alle können von jemandem umarmt werden oder jemanden umarmen, etwa weil sie einsam, alleinstehend oder isoliert sind. Bei Pandemien besteht die Gefahr einer ungenügenden Anzahl von Umarmungen auch bei der breiten Bevölkerung. Soziale Roboter können Menschen umarmen, Menschen können soziale Roboter umarmen. Die Frage ist, ob der Wunsch danach überhaupt besteht, was die Wirkung und was der Nutzen einer robotischen Berührung ist und wie man durch gestalterische und technische Maßnahmen das Wohlbefinden bei einer robotischen Umarmung verbessern kann. Der vorliegende Beitrag geht zunächst auf die Theorie der Umarmung ein und sammelt einige Fakten und Resultate von Studien hierzu. Dann untersucht er die Möglichkeit robotischer Umarmungen. Schließlich wird eine Onlineumfrage mit fast 300 Teilnehmerinnen und Teilnehmern, die 2020 an der Hochschule für Wirtschaft FHNW durchgeführt wurde, vorgestellt und zusammengefasst.
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First published in 1995, this book presents a model for understanding the visual processing underlying perception and action, proposing a broad distinction within the brain between two kinds of vision: conscious perception and unconscious 'online' vision. It argues that each kind of vision can occur quasi-independently of the other, and is separately handled by a quite different processing system. For this new edition, the text from the original edition has been left untouched, standing as a coherent statement of the authors' position. However, a very substantial epilogue has been added to the book, which reviews some of the key developments that support or challenge the views that were put forward in the first edition. The new chapter summarizes developments in various relevant areas of psychology, neuroscience, and behaviour. It supplements the main text by updating the reader on the contributions that have emerged from the use of functional neuroimaging, which was in its infancy when the first edition was written. Neuroimaging, and functional MRI in particular, has revolutionized the field by allowing investigators to plot in detail the patterns of activity within the visual brains of behaving and perceiving humans. The authors show how its use now allows scientists to test and confirm their proposals, based largely on evidence accrued from primate neuroscience in conjunction with studies of neurological patients.
This review addresses the role of early sensory areas in the awareness of tactile information in humans. The results of recent studies dealing with this important topic are critically discussed: In particular, we report on evidence from neuropsychology, neurophysiology, neuroimaging, and behavioral experiments that have highlighted the crucial role played by the primary somatosensory cortex (SI) in mediating our awareness of tactile information. Phenomena, such as tactile hallucinations, tactile illusions, the perception of supernumerary limbs, and synaesthesia are also discussed. The research reviewed here clearly shows that the activation of SI is necessary, but not sufficient, for the awareness of touch. On the basis of the evidence outlined here, we propose a neurocognitive model that provides a conceptual framework in which to interpret the results of the literature regarding tactile consciousness. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
In macaque monkeys, the posterior parietal cortex (PPC) is concerned with the integration of multimodal information for constructing a spatial representation of the external world (in relation to the macaque's body or parts thereof), and planning and executing object-centred movements. The areas within the intraparietal sulcus (IPS), in particular, serve as interfaces between the perceptive and motor systems for controlling arm and eye movements in space. We review here the latest evidence for the existence of the IPS areas AIP (anterior intraparietal area), VIP (ventral intraparietal area), MIP (medial intraparietal area), LIP (lateral intraparietal area) and CIP (caudal intraparietal area) in macaques, and discuss putative human equivalents as assessed with functional magnetic resonance imaging. The data suggest that anterior parts of the IPS comprising areas AIP and VIP are relatively well preserved across species. By contrast, posterior areas such as area LIP and CIP have been found more medially in humans, possibly reflecting differences in the evolution of the dorsal visual stream and the inferior parietal lobule. Despite interspecies differences in the precise functional anatomy of the IPS areas, the functional relevance of this sulcus for visuomotor tasks comprising target selections for arm and eye movements, object manipulation and visuospatial attention is similar in humans and macaques, as is also suggested by studies of neurological deficits (apraxia, neglect, Bálint's syndrome) resulting from lesions to this region.