Stimulating Illusory Own-Body Perceptions

Article (PDF Available)inNature 419(6904):269-70 · October 2002with 993 Reads 
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
DOI: 10.1038/419269a · Source: PubMed
Cite this publication
Abstract
'Out-of-body' experiences (OBEs) are curious, usually brief sensations in which a person's consciousness seems to become detached from the body and take up a remote viewing position. Here we describe the repeated induction of this experience by focal electrical stimulation of the brain's right angular gyrus in a patient who was undergoing evaluation for epilepsy treatment. Stimulation at this site also elicited illusory transformations of the patient's arm and legs (complex somatosensory responses) and whole-body displacements (vestibular responses), indicating that out-of-body experiences may reflect a failure by the brain to integrate complex somatosensory and vestibular information.
‘O
ut-of-body’ experiences (OBEs)
are curious, usually brief sensa-
tions in which a persons con-
sciousness seems to become detached from
the body and take up a remote viewing
position
1–3
. Here we describe the repeated
induction of this experience by focal
electrical stimulation of the brains right
angular gyrus in a patient who was under-
going evaluation for epilepsy treatment.
Stimulation at this site also elicited illusory
transformations of the patients arm and
legs (complex somatosensory responses)
and whole-body displacements (vestibular
responses), indicating that out-of-body
experiences may reflect a failure by the
brain to integrate complex somatosensory
and vestibular information
1–3
.
Our patient was a 43-year-old, right-
handed woman who had suffered from
complex partial seizures for 11 years; right
temporal-lobe epilepsy was implicated. As
magnetic-resonance imaging did not reveal
any lesion, invasive monitoring was under-
taken to localize the seizure focus precisely.
Subdural electrodes were implanted to
record seizures, and focal electrical stimula-
tion was used to identify the vital cortex
4
.
Figure 1 shows the results of stimulation
mapping and the electrode site on the right
angular gyrus where stimulation repeatedly
induced OBEs, as well as vestibular and
complex somatosensory responses. Map-
ping of motor,somatosensory and auditory
functions revealed no deviant brain pathol-
ogy in this patient with respect to anatomi-
cal representations of cortical functions.
The epileptic focus was located more than
5 cm anterior to the stimulation site,in the
medial temporal lobe; electrical stimulation
of this site did not induce OBEs, and these
experiences were not part of the patient’s
habitual seizures.
Initial stimulations (n43; 2.0–3.0 mA)
induced vestibular responses, in which the
patient reported that she was “sinking into
the bed”or falling from a height”. Increas-
ing the current amplitude (3.5 mA) led to
an OBE (“I see myself lying in bed, from
above, but I only see my legs and lower
trunk”). Two further stimulations induced
the same sensation, which included an
instantaneous feeling of “lightness” and
“floating about two metres above the bed,
close to the ceiling.
The patient was then asked to watch her
(real) legs during the electrical stimulation
(n42; 4.0,4.5 mA).As before,she was lying
down (upper body supported at an angle
of 457, legs outstretched). This time, she
reported seeing her legs “becoming shorter”.
If the patient’s legs were bent before the
stimulation (907 knee angle; n42; 4.0, 5.0
mA), she reported that her legs appeared to
be moving quickly towards her face, and
took evasive action.
When asked to look at her outstretched
arms during the electrical stimulation
(n42; 4.5, 5.0 mA), the patient felt as
though her left arm was shortened; the
right arm was unaffected.If both arms were
in the same position but bent by 907 at the
elbow, she felt that her left lower arm and
hand were moving towards her face (n42;
4.5, 5.0 mA). When her eyes were shut,
she felt that her upper body was moving
towards her legs, which were stable (n42;
4.0,5.0 mA).
These observations indicate that OBEs
and complex somatosensory illusions can
be artificially induced by electrical stimula-
tion of the cortex. The association of these
phenomena and their anatomical selectivity
suggest that they have a common origin in
body-related processing
1–3
, an idea that is
supported by the restriction of these visual
experiences to the patients own body.
During her OBE, the patient only ‘saw’
that part of her body that she also felt was
modified during her body-transformation
experiences. This contrasts with the non-
corporeal visual hallucinations that are
commonly induced by electrical stimula-
tion at the parieto-temporal junction
5
.As
suggested by previous neurological investiga-
tions on OBEs
1–3
and other body-cognition
disorders
6–8
, the angular gyrus could be a
crucial node in a larger neural circuit that
mediates complex own-body perception.
Out-of-body and body-transformation
experiences are transitory and may disap-
pear when a person attempts to inspect the
illusory body or body part
1–3
. Our findings
suggest that changes in visual attention
and/or current amplitude in the angular
gyrus
4,9
could bring about these phenom-
enological modifications.
Although we do not fully understand
the neurological mechanism that causes
OBEs,our results imply that vestibular pro-
cessing
2
may be important.Although trans-
lational vestibular responses were evoked
initially without an OBE and can be pro-
duced in isolation
4
, vestibular sensations
of levitation and lightness
1–3
accompanied
OBEs in our patient. Also, the core region
of the human vestibular cortex is situated
close to the angular gyrus
10
. It is possible
that the experience of dissociation of self
from the body is a result of failure to
integrate complex somatosensory and
vestibular information.
Olaf Blanke*†,Stéphanie Ortigue†,
Theodor Landis†, Margitta Seeck*
*Laboratory of Presurgical Epilepsy Evaluation,
Program of Functional Neurology and
Neurosurgery, University Hospitals of Geneva and
Lausanne, Geneva 1211 and Lausanne 1011,
Switzerland
e-mail: olaf.blanke@hcuge.ch
Functional Brain Mapping Laboratory,
Department of Neurology, Geneva University
Hospital, 1211 Geneva, Switzerland
brief communications
NATURE
|
VOL 419
|
19 SEPTEMBER 2002
|
www.nature.com/nature 269
Stimulating illusory own-body perceptions
The part of the brain that can induce out-of-body experiences has been located.
Figure 1 Three-dimensional
surface reconstruction of the
right hemisphere of the
brain from magnetic-reso-
nance imaging. Subdural elec-
trodes were implanted in the
brain of an epileptic patient
undergoing presurgical evalu-
ation; the locations at which
focal electrical stimulation (ES)
evoked behavioural responses
are shown: magenta, motor;
green, somatosensory cortex;
turquoise, auditory cortex.
Yellow, site at which out-of-
body experience (OBE), body-
part illusions and vestibular
responses were induced
(arrow). Stars indicate the
epileptic focus in the medial
temporal lobe. Informed con-
sent was obtained from the patient and ES procedures conformed to the Declaration of Helsinki. Constant current (0.5–5.0 mA,2-s train
duration) was applied at 50 Hz in a bipolar manner through adjacent contacts
4
. Since undergoing a right anterior temporal lobectomy in
2000,the patient has been free of complex partial seizures.
© 2002
Nature
Publishing
Group
Carpediemonas membranifera, that have
boundary sequences of the normal eukary-
otic type, indicating that canonical introns
are likely to have arisen very early in
eukaryotic evolution.
Carpediemonas membranifera is a poorly
studied,free-living microbial eukaryote that
is considered to be a relative of Giardia on
the basis of its morphology
4
. Using the
polymerase chain reaction (PCR) with Car-
pediemonas genomic DNA as template, we
determined the partial sequences of two
distinct carbamate kinase genes from this
organism. In both genes, an insertion of
33 or 31 nucleotides interrupts the similar
protein-coding sequence shared with carba-
mate kinase genes from other organisms
(Fig. 1a). These insertions are bounded by
guanine and thymine (GT) nucleotides at
the 58 end and adenine and guanine (AG)
nucleotides at the 38 end,which is a charac-
teristic of most of the spliceosomal introns
that interrupt protein-coding genes in
other eukaryotes.
We used PCR with reverse transcription
to recover the messenger RNA sequence of
one of the two Carpediemonas carbamate
kinase genes. This sequence lacks the inser-
tion,which is presumably removed (spliced)
from the messenger RNA before translation.
We conclude that the insertions in the Car-
pediemonas carbamate kinase genes are
canonical ‘GT…AG’ spliceosomal introns,
albeit comparatively small ones.
To determine the evolutionary affinities
of Carpediemonas, we used PCR to amplify
near-complete sequences for two genes that
encode cytosolic heat-shock protein 70
(Hsp70).We also sequenced a cloned Hsp70
gene from Spironucleus barkhanus,a very
close relative of Giardia. Maximum likeli-
hood analysis of Hsp70 proteins reveals a
specific evolutionary relation between Car-
pediemonas, Giardia and Spironucleus (Fig.
1b); three other molecular markers also
support this relationship
5
.
The single intron found in a Giardia
gene has a non-canonical CT dinucleotide
at its 58 splicing boundary
3
, which could
be interpreted as a ‘frozen’ primitive
eukaryotic condition: canonical ‘GT…AG’
spliceosomal introns might then be a later
innovation in more modern cells. Our
results indicate that this is not the case,
however, as canonical introns seem to be an
ancestral feature of the larger evolutionary
grouping that includes Giardia and Car-
pediemonas. The aberrant Giardia intron
probably represents a lineage-specific (or
intron-specific) secondary alteration of the
58 splice boundary.
The extremely early divergence attrib-
uted to Giardia is based on the absence or
aberration of many typical eukaryotic
features, such as mitochondria and introns,
and on its arguably deep-branching posi-
tion in many phylogenetic trees
6–9
.The
grouping of Giardia with Carpediemonas
(which, as well as canonical introns, has
organelles that are probably derived from
mitochondria
4
) weakens this argument for
early divergence.
Irrespective of the true evolutionary
position of Giardia, the only potentially
early’ eukaryotic group in which introns
have not been found are the parabasalids,
such as Trichomonas
10,11
. Trichomonas is
already known to possess some of the cellu-
lar machinery for intron splicing
12
,how-
ever, and there is evidence to indicate that it
is evolutionarily affiliated with Giardia and
its relatives
7,13
(and is slightly misplaced in
many phylogenies, including that shown in
Fig. 1b).An affiliation with Giardia implies
a similar closeness to Carpediemonas, and
it is likely that parabasalids have, or had,
canonical introns. There is now every
reason to assume that canonical introns
were present in the most recent common
ancestor of living eukaryotes.
Alastair G.B. Simpson,Erin K. MacQuarrie,
Andrew J. Roger
Canadian Institute for Advanced Research,
Program in Evolutionary Biology, Department of
Biochemistry and Molecular Biology, Dalhousie
University, Halifax, Nova Scotia B3H 4H7, Canada
e-mail: simpson@hades.biochem.dal.ca
1. Palmer,J. D. & Logsdon, J. M. Curr. Opin. Genet. Dev. 1,
470–477 (1991).
2. Logsdon, J. M. Curr. Opin. Genet. Dev. 8, 637–648 (1998).
3. Nixon, J. E. J. et al.Proc. Natl Acad. Sci. USA 99, 3701–3705
(2002).
4. Simpson, A. G.B. & Patterson, D. J.Eur. J. Protistol. 35, 353–370
(1999).
5. Simpson, A. G.B. et al. Mol. Biol. Evol. 19, 1782–1791 (2002).
6. Cavalier-Smith, T. Trends Genet. 7, 145–148 (1991).
7. Embley, T. M. & Hirt, R.P. Curr. Opin. Genet. Dev. 8, 624–629
(1998).
8. Roger,A.J. Am. Nat. 154 (suppl.),146–163 (1999).
9. Sogin, M.L. Curr. Opin. Genet. Dev. 7, 792–799 (1997).
10.Johnson,P. J.Proc. Natl Acad. Sci. USA 99, 3359–3361 (2002).
11.Archibald, J.M., O’Kelly,C. J.& Doolittle, W. F. Mol. Biol. Evol.
19, 422–431 (2002).
12.Fast,N. M., Logsdon,J. M.& Doolittle, W. F.Mol. Biochem.
Parasitol. 99, 514–522 (1999).
13.Dacks,J. B.& Roger,A. J. J. Mol. Evol. 48, 779–783 (1999).
Competing financial interests: declared none.
270 NATURE
|
VOL 419
|
19 SEPTEMBER 2002
|
www.nature.com/nature
Eukaryotic evolution
Early origin of
canonical introns
S
pliceosomal introns, one of the hall-
marks of eukaryotic genomes, were
thought to have originated late in evo-
lution
1,2
and were assumed not to exist
in eukaryotes that diverged early — until
the discovery of a single intron with an
aberrant splice boundary in the primitive
‘protozoan Giardia
3
. Here we describe
introns from a close relative of Giardia,
brief communications
Giardia
Spironucleus
Alveolates
Stramenopiles
Plants + green algae
Nucleomorphs
Kinetoplastids
Entamoeba
Animals
Fungi
Cryptomonad
Slime mould
Trichomonas
61/71
Carpediemonas 2
BiP
(outgroup)
CT...AG
GT...AG
Origin of
canonical
introns
????
49/87
Carpediemonas 1
G
G
F
Y
I
I
a
b
Figure 1 Introns and evolutionary affinities of
Carpediemonas.
a,
Portions of two
Carpediemonas
carbamate kinase genes, showing
intron sequences (red) interrupting the protein-coding sequence
(in blue).The introns have canonical splice boundaries (GT…AG;
large red type). b, Maximum-likelihood evolutionary tree of
eukaryotic cytosolic Hsp70 proteins (‘G&invariable sites’ model).
Endoplasmic-reticulum Hsp70 (‘BiP’) is used as an outgroup.The
grouping of
Carpediemonas
with
Giardia
and
Spironucleus
is
shown in the blue box; statistical support (bootstrap percentages)
for this grouping is assessed using likelihood (upper left of box),
and likelihood distance (lower left).The higher percentages (right
in each pair) apply when the outgroup is omitted.The basal place-
ment of
Trichomonas
is weakly supported with likelihood (21%);
green arrow shows a more plausible position on the basis of other
evidence
7,13
.The intron splice boundaries for the relevant groups
and the origin of canonical introns are shown in red. New
sequences have been deposited at GenBank under accession
numbers AY131204–AY131209.
brief communications is intended to provide a forum for both brief,topical reports of general scientific interest and
technical discussion of recently published material of particular interest to non-specialist readers.Priority will be given
to contributions that have fewer than 500 words,10 references and only one figure.Detailed guidelines are available on
Nature
s website (www.nature.com) or on request from nature@nature.com
1. Brugger, P., Regard, M. & Landis,T. Cogn. Neuropsychiatr. 2,
19–38 (1997).
2. Grüsser,O. J. & Landis,T. Visual Agnosias and Other
Disturbances of Visual Perception and Cognition 297–303
(Macmillan,Amsterdam, 1991).
3. Hécaen, H. & Ajuriaguerra, J. Méconnaissances et Hallucinations
Corporelles 310343 (Masson,Paris, 1952).
4. Blanke, O., Perrig, S.,Thut, G., Landis,T. & Seeck,M. J. Neurol.
Neurosurg.Psychiatr. 69, 553–556 (2000).
5. Penfield,W. & Perot, P. Brain 86, 595–696 (1963).
6. Damasio, A.The Feeling of What Happens: Body, Emotions and
the Making of Consciousness 213–215 (Vintage,London,2000).
7. Worthington, A.& Beevers,L. Neurocase 2, 135–140 (1996).
8. Halligan, P. W., Marshall,J. C. & Wade, D. T. Cortex 31, 173–182
(1995).
9. Nathan, S. S.,Sinha, S. R.,Gordon, B.,Lesser,R. P. & Thakor,
N.V. Electroencephalogr. Clin. Neurophysiol. 86, 183–192 (1993).
10.Lobel,E., Kleine, J., Leroy-Wilig, A.,Le Bihan, D. & Berthoz, A.
J. Neurophysiol. 80, 2699–2709 (1998).
Competing financial interests: declared none.
© 2002
Nature
Publishing
Group
  • ... Als ein namhafter Proponent dieser Interpretation von Autoskopien kann Olaf Blanke angesehen werden (z. B. Aspell & Blanke, 2009;Blanke, 2012;Blanke, Landis, Spinelli & Seeck, 2004;Blanke & Mohr, 2005;Blanke, Ortigue, Landis & Seeck, 2002). Auch dort, wo Autoskopien explizit im Zusammenhang mit NTE diskutiert werden, geht man offenbar davon aus, dass diese in Echtzeit erlebt werden und sie durch Funktionsbeeinträchtigungen der genannten Gehirnregion ausgelöst werden, vor allem in der rechten Hemisphäre (Blanke & Dieguez, 2009). ...
    Article
    Full-text available
    Noch immer sind die physiologischen und psychologischen Grundlagen von Nahtod-Erfahrungen (NTE) nicht geklärt. In diesem Aufsatz zeigen wir, dass bislang auch für "kriti-sche" NTE, die nach einem Herzstillstand auftreten, zwei verschiedene neuro-physiologische Modelle aufgestellt wurden, die in der Literatur jedoch nicht gebührend voneinander getrennt worden sind. Im ersten Modell wird postuliert, dass auch in kritischen NTE noch genügend Restaktivität im Großhirn bestanden hat, um die NTE gewissermaßen in Echtzeit zu generieren. Im zweiten Modell wird hin-gegen angenommen, dass sich kritische NTE aufgrund der herrschenden Sauerstoffunterversorgung nicht in Echtzeit ereignet haben können, sondern dass sie später während der Regenerationsphase des Gehirns rekonstruiert worden sind. Um die Plausibilität der beiden Modelle zu analysieren, ziehen wir die Phänomenologie der Selbstschau des eigenen Körpers heran (Autoskopie), die NTE häufig einleitet. Nebst der verfügbaren Literatur greifen wir hierfür auch auf Originalschilderungen von Au-toskopien zurück, die im Rahmen einer in 2015 durchgeführten Online-Befragung gewonnen wurden. Insgesamt zeigt sich, dass das Rekonstruktionsmodell bislang durch keine empirischen Befunde ge-stützt wird und dass einige Befunde sogar gegen es sprechen. Hierzu zählt u.a. das vollständige Fehlen von Autoskopieberichten, die sich auf die Zeit der Regenerationsphase des Gehirns beziehen, obwohl im Rekonstruktionsmodell gemäß dem gegenwärtigen Forschungsstand zu Autoskopien genau solche Berichte erwartet werden müssten. Zukünftige Diskussionen um Erklärungsmodelle von NTE soll-ten sich daher vornehmlich mit dem Echtzeit-Modell sowie einem dritten Modell befassen, wonach Autoskopien und NTE auch in relativer Unabhängigkeit von den jeweils herrschenden neurophysiolo-gischen Prozessen im Gehirn auftreten können.
  • ... Its involvement was repeatedly reported in monitoring multi-step action execution (Hartmann et al., 2005), visuo-proprioceptive conflict (Balslev et al., 2005), spatial re-orientation (Corbetta et al., 2000), and detection of environmental changes across visual, auditory, or tactile stimulation (Downar et al., 2000). Direct electrical stimulation of the human RTPJ during neurosurgery was associated with altered perception and stimulus awareness (Blanke et al., 2002). It was argued that the RTPJ encodes actions and predicted outcomes, without necessarily relating these neural processes to value estimation (Rutledge et al., 2009;Liljeholm et al., 2013;Hamilton and Grafton, 2008;Jakobs et al., 2009). ...
    Article
    Full-text available
    The default mode network (DMN) is believed to subserve the baseline mental activity in humans. Its higher energy consumption compared to other brain networks and its intimate coupling with conscious awareness are both pointing to an unknown overarching function. Many research streams speak in favor of an evolutionarily adaptive role in envisioning experience to anticipate the future. In the present work, we propose a process model that tries to explain how the DMN may implement continuous evaluation and prediction of the environment to guide behavior. The main purpose of DMN activity, we argue, may be described by Markov Decision Processes that optimize action policies via value estimates based through vicarious trial and error. Our formal perspective on DMN function naturally accommodates as special cases previous interpretations based on (1) predictive coding, (2) semantic associations, and (3) a sentinel role. Moreover, this process model for the neural optimization of complex behavior in the DMN offers parsimonious explanations for recent experimental findings in animals and humans.
  • ... 37 In particular, the temporoparietal junction is a multisensory region critical for self-location and firstperson perspective, and neurologically or electrophysiologically induced alterations of this area have been shown to induce altered states of self-consciousness such as the so-called out-of-body experiences and PH. 44,45 The insular cortex is considered a fundamental cortical hub integrating interoceptive and exteroceptive stimuli [45][46][47][48][49] and is involved in bodily self-representation 49,50 and source monitoring. 51 Insular lesions have been linked to distortions in bodily experience, such as somatoparaphrenia 50 and heautoscopy. ...
    Article
    Dysfunction of sensorimotor predictive processing is thought to underlie abnormalities in self-monitoring producing passivity symptoms in psychosis. Experimentally induced sensorimotor conflict can produce a failure in bodily self-monitoring (presence hallucination [PH]), yet it is unclear how this is related to auditory self-monitoring and psychosis symptoms. Here we show that the induction of sensorimotor conflict in early psychosis patients induces PH and impacts auditory-verbal self-monitoring. Participants manipulated a haptic robotic system inducing a bodily sensorimotor conflict. In experiment 1, the PH was measured. In experiment 2, an auditory-verbal self-monitoring task was performed during the conflict. Fifty-one participants (31 early psychosis patients, 20 matched controls) participated in the experiments. The PH was present in all participants. Psychosis patients with passivity experiences (PE+) had reduced accuracy in auditory-verbal self-other discrimination during sensorimotor stimulation, but only when sensorimotor stimulation involved a spatiotemporal conflict (F(2, 44) = 6.68, P = .002). These results show a strong link between robotically controlled alterations in sensorimotor processing and auditory misattribution in psychosis and provide evidence for the role of sensorimotor processes in altered self-monitoring in psychosis.
  • ... However, in other patients with autoscopic hallucinations, no posterior cortical neuropsychological deficits have been confirmed (Heydrich & Blanke, 2013). Autoscopic phenomena may also occur without major neuropsychological deficits and without impairment of consciousness, as observed in healthy individuals and when induced by focal electrical stimulation of cortical regions (Arzy, Seeck, Ortigue, Spinelli, & Blanke, 2006;Blanke, Ortigue, Landis, & Seeck, 2002;De Ridder, Van Laere, Dupont, Menovsky, & Van de Heyning, 2007). Various neuropsychiatric symptoms, including depression and suicidal ideation (Brugger et al., 1994), depersonalization and dissociative disorders (Lopez, Nakul, Preuss, Elziere, & Mast, 2018;Simeon et al., 2000) have been associated with autoscopic phenomena. ...
  • Article
    Full-text available
    Introduction There is currently no general agreement on how to best conceptualize dissociative symptoms and whether they share similar neural underpinnings across dissociative disorders. Neuroimaging data could help elucidate these questions. Objectives The objective of this review is to summarize empirical evidence for neural aberrations observed in patients suffering from dissociative symptoms. Methods A systematic literature review was conducted including patient cohorts diagnosed with primary dissociative disorders, post-traumatic stress disorder (PTSD), or borderline personality disorder. Results Results from MRI studies reporting structural (gray matter and white matter) and functional (during resting-state and task-related activation) brain aberrations were extracted and integrated. In total, 33 articles were included of which 10 pertained to voxel-based morphology, 2 to diffusion tensor imaging, 10 to resting-state fMRI, and 11 to task-related fMRI. Overall findings indicated aberrations spread across diverse brain regions, especially in the temporal and frontal cortices. Patients with dissociative identity disorder and with dissociative PTSD showed more overlap in brain activation than each group showed with depersonalization/derealization disorder. Conclusion In conjunction, the results indicate that dissociative processing cannot be localized to a few distinctive brain regions but rather corresponds to differential neural signatures depending on the symptom constellation.
  • Article
    Full-text available
    A prominent theory claims the right temporoparietal junction (rTPJ) is especially associated with embodied processes relevant to perspective taking. In the present study we use high-definition transcranial direct current stimulation (HD-tDCS) to provide evidence that the rTPJ is causally associated with the embodied processes underpinning perspective taking. Eighty-eight young human adults were stratified to receive either rTPJ or dorsomedial prefrontal (dmPFC) anodal HD-tDCS in a sham-controlled, double-blind, repeated-measures design. Perspective tracking (line-of-sight) and perspective taking (embodied rotation) were assessed using a visuo-spatial perspective taking (VPT) task that required understanding what another person could see or how they see it, respectively. Embodied processing was manipulated by positioning the participant in a manner congruent or incongruent with the orientation of an avatar on the screen. As perspective taking, but not perspective tracking, is influenced by bodily position, this allows the investigation of the specific causal role for the rTPJ in embodied processing. Crucially, anodal stimulation to the rTPJ increased the effect of bodily position during perspective taking, whereas no such effects were identified during perspective tracking, thereby providing evidence for a causal role for the rTPJ in the embodied component of perspective taking. Stimulation to the dmPFC had no effect on perspective tracking or taking. Therefore, the present study provides support for theories postulating that the rTPJ is causally involved in embodied cognitive processing relevant to social functioning.Significance StatementThe ability to understand another's perspective is a fundamental component of social functioning. Adopting another perspective is thought to involve both embodied and non-embodied processes. The present study used high-definition transcranial direct current stimulation (HD-tDCS) and provided causal evidence that the right temporoparietal junction (rTPJ) is involved specifically in the embodied component of perspective taking. Specifically, HD-tDCS to the rTPJ, but not another hub of the social brain (dmPFC), increased the effect of body position during perspective taking, but not tracking. This is the first causal evidence that HD-tDCS can modulate social embodied processing in a site-specific and task-specific manner.
  • Article
    The subjective experience of supernumerary phantom limb is a complex cognitive and perceptual distortion which is occasionally reported after right hemisphere lesions. Following a report by Halligan and colleagues, published in 1993, we describe the case of another patient, MP, who sustained a right middle cerebral artery infarct and subsequently developed a belief in the existence of a supernumerary phantom left hand, which could not be attributed to more general intellectual or perceptual disturbance. In comparison with previously reported cases a number of common features emerged from MP with taxonomic implications. However, the need to consider the contributory role of idiosyncratic psychological factors is also emphasized.
  • With the use of a 3-dimensional finite element model of the human brain based on structural data from MRI scans, we simulated patterns of current flow in the cerebral hemisphere with different types of electrical stimulation. Five different tissue types were incorporated into the model based on conductivities taken from the literature. The boundary value problem derived from Laplace's equation was solved with a quasi-static approximation. Transcranial electrical stimulation with scalp electrodes was poorly focussed and required high levels of current for stimulation of the cortex. Direct cortical stimulation with bipolar (adjacent) electrodes was found to be very effective in producing localized current flows. Unipolar cortical stimulation (with a more distant reference electrode) produced higher current densities at the same stimulating current as did bipolar stimulation, but stimulated a larger region of the cortex. With the simulated electrodes resting on the pia-arachnoid, as usually occurs clinically, there was significant shunting of the current (7/8 of the total current) through the CSF. Possible changes in electrodes and stimulation parameters that might improve stimulation procedures are considered.
  • Article
    We report a case of somatoparaphrenia in a 41 year-old man after right temporo-parietal stroke. An elaborate system of delusional beliefs was observed concerning the initially paralysed left leg, arm, and hand. The course of these beliefs is analysed as the patient progresses from a full-blown delusional state to having excellent insight into his condition. We outline the types of explantation that seem required to understand how somatoparaphrenic beliefs can arise.
  • Article
    Full-text available
    The cortical processing of vestibular information is not hierarchically organized as the processing of signals in the visual and auditory modalities. Anatomic and electrophysiological studies in the monkey revealed the existence of multiple interconnected areas in which vestibular signals converge with visual and/or somatosensory inputs. Although recent functional imaging studies using caloric vestibular stimulation (CVS) suggest that vestibular signals in the human cerebral cortex may be similarly distributed, some areas that apparently form essential constituents of the monkey cortical vestibular system have not yet been identified in humans. Galvanic vestibular stimulation (GVS) has been used for almost 200 years for the exploration of the vestibular system. By contrast with CVS, which mediates its effects mainly via the semicircular canals (SCC), GVS has been shown to act equally on SCC and otolith afferents. Because galvanic stimuli can be controlled precisely, GVS is suited ideally for the investigation of the vestibular cortex by means of functional imaging techniques. We studied the brain areas activated by sinusoidal GVS using functional magnetic resonance imaging (fMRI). An adapted set-up including LC filters tuned for resonance at the Larmor frequency protected the volunteers against burns through radio-frequency pickup by the stimulation electrodes. Control experiments ensured that potentially harmful effects or degradation of the functional images did not occur. Six male, right-handed volunteers participated in the study. In all of them, GVS induced clear perceptions of body movement and moderate cutaneous sensations at the electrode sites. Comparison with anatomic data on the primate cortical vestibular system and with imaging studies using somatosensory stimulation indicated that most activation foci could be related to the vestibular component of the stimulus. Activation appeared in the region of the temporo-parietal junction, the central sulcus, and the intraparietal sulcus. These areas may be analogous to areas PIVC, 3aV, and 2v, respectively, which form in the monkey brain, the "inner vestibular circle". Activation also occurred in premotor regions of the frontal lobe. Although undetected in previous imaging-studies using CVS, involvement of these areas could be predicted from anatomic data showing projections from the anterior ventral part of area 6 to the inner vestibular circle and the vestibular nuclei. Using a simple paradigm, we showed that GVS can be implemented safely in the fMRI environment. Manipulating stimulus waveforms and thus the GVS-induced subjective vestibular sensations in future imaging studies may yield further insights into the cortical processing of vestibular signals.
  • Article
    Full-text available
    The present study reports on a patient undergoing invasive monitoring for intractable epilepsy who experienced different vestibular sensations after electrical cortical stimulation of the inferior parietal lobule at the anterior part of the intraparietal sulcus. Types of vestibular response ranged from simple to complex sensations and depended on stimulation site and applied current. The findings suggest vestibular topography and hierarchical processing within the parietal vestibular cortex of humans.