Stimulating Illusory Own-Body Perceptions

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DOI: 10.1038/419269a · Source: PubMed
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'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.
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
. 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
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
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
, 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
suggested by previous neurological investiga-
tions on OBEs
and other body-cognition
, 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
. Our findings
suggest that changes in visual attention
and/or current amplitude in the angular
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-
may be important.Although trans-
lational vestibular responses were evoked
initially without an OBE and can be pro-
duced in isolation
, vestibular sensations
of levitation and lightness
OBEs in our patient. Also, the core region
of the human vestibular cortex is situated
close to the angular gyrus
. 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,
Functional Brain Mapping Laboratory,
Department of Neurology, Geneva University
Hospital, 1211 Geneva, Switzerland
brief communications
VOL 419
| 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
. Since undergoing a right anterior temporal lobectomy in
2000,the patient has been free of complex partial seizures.
© 2002
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
. 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
The single intron found in a Giardia
gene has a non-canonical CT dinucleotide
at its 58 splicing boundary
, 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
grouping of Giardia with Carpediemonas
(which, as well as canonical introns, has
organelles that are probably derived from
) 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
. Trichomonas is
already known to possess some of the cellu-
lar machinery for intron splicing
ever, and there is evidence to indicate that it
is evolutionarily affiliated with Giardia and
its relatives
(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
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
4. Simpson, A. G.B. & Patterson, D. J.Eur. J. Protistol. 35, 353–370
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
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.
VOL 419
Eukaryotic evolution
Early origin of
canonical introns
pliceosomal introns, one of the hall-
marks of eukaryotic genomes, were
thought to have originated late in evo-
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
. Here we describe
introns from a close relative of Giardia,
brief communications
Plants + green algae
Slime mould
Carpediemonas 2
Origin of
Carpediemonas 1
Figure 1 Introns and evolutionary affinities of
Portions of two
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
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
is weakly supported with likelihood (21%);
green arrow shows a more plausible position on the basis of other
.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
s website ( or on request from
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
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
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