Correspondence
Visualizing Out-of-Body Experience in the Brain
N Engl J Med 2008; 358:855-856February 21, 2008
- Article
To the Editor:
The single-subject study design used by De Ridder et al. (Nov. 1 issue)1 makes it difficult to conclude whether the changes seen on positron-emission tomography (PET) were due to out-of-body experiences or simply to the differential effects of stimulation at 3.7 V in 40-Hz burst mode as compared with other modes, a confounder that has not been controlled for. A more robust approach would be to compare this patient with a group of patients with tinnitus, but without the out-of-body experiences, receiving the same stimulation. Furthermore, the short duration of the out-of-body experiences in this patient (average duration, 17 seconds, starting within 1 second after stimulation) means that the experiences had almost disappeared by the time the scans started (10 seconds after stimulation started). Therefore, it is possible that most of the PET changes reported in this study, despite being consistent with the authors' hypothesis, were due to the effects of stimulation alone.
1 ReferencesYen F. Tai, M.R.C.P.
Imperial College London, London W12 0NN, United Kingdom
yen.tai@imperial. ac. uk 1
De Ridder D ,Van Laere K ,Dupont P , et al. Visualizing out-of-body experience in the brain. N Engl J Med 2007;357:1829-1833
Full Text | Web of Science | Medline
To the Editor:
The report by De Ridder and colleagues describing a sense of disembodiment elicited by temporoparietal-junction stimulation in a patient with tinnitus extends similar findings in patients with epilepsy.1 We should be cautious, however, about drawing analogies between an induced sense of disembodiment and spontaneous out-of-body experiences. That they have similar neuroanatomical loci is a plausible hypothesis but an untested one.
The sense of disembodiment induced by electrical stimulation is limited to a fixed location; those in whom this experience is induced by stimulation perceive the environment from the visual perspective of the physical body, and they perceive the event as illusory. Spontaneous out-of-body experiences often involve accurate perception of the environment (including the physical body) from an extracorporeal visual perspective; the disembodied center of consciousness may seem to move about independently of the physical body, and those who have such a spontaneous experience usually perceive the event as profoundly real.2,3 Given the differences in phenomenology and in psychological aftereffects for those who have the experience, it is premature to assume that the mechanism of an induced sense of disembodiment also applies to spontaneous experiences.4
4 ReferencesBruce Greyson, M.D.
University of Virginia, Charlottesville, VA 22908-0152
cbg4d@virginia.edu Sam Parnia, M.D., Ph.D.
Weill Cornell Medical Center, New York, NY 10021Peter Fenwick, M.D.
King's College Institute of Psychiatry, London SE5 8AF, United Kingdom1
Blanke O ,Ortigue S ,Landis T ,Seeck M . Stimulating illusory own-body perceptions. Nature 2002;419:269-270
CrossRef | Web of Science | Medline2
Gabbard GO ,Twemlow SW ,Jones FC . Differential diagnosis of altered mind/body perception. Psychiatry 1982;45:361-369
Web of Science | Medline3
Gabbard GO, Twemlow SW. With the eyes of the mind: an empirical analysis of out-of-body states. New York: Praeger, 1984.
4
Alvarado CS. Out-of-body experiences. In: Cardeña E, Lynn SJ, Krippner SC, eds. Varieties of anomalous experience: examining the scientific evidence. Washington, DC: American Psychological Association, 2000:183-218.
Author/Editor Response
In response to Tai's comments, comparison of the patient with a group of patients receiving the same stimulation without out-of-body experiences is practically impossible because of the interindividual variability of the anatomy of this area, both topographically (1.5 to 2.0 cm)1 and morphologically, which precludes delivery of an identical stimulus2 at the exact same functional area and thus comparable data.
Regarding PET signal interpretation, we argue that it is unlikely that the PET changes reported simply reflect the effects of stimulation alone and not the out-of-body experience. Stimulation started about 35 seconds after the start of the tracer injection (10 seconds before the start of the scan) and lasted until the end of the scan. The start of the scan was initiated by the sharp increase in the intracranial radioactivity count rate on the acquisition monitor, thereby capturing the full out-of-body experience. Nevertheless, we agree that even with this optimal acquisition, the out-of-body experience was reported by the subject only in the first 15 to 20 seconds after stimulation; thus, only a portion of the PET signal reflected the perfusion changes during the out-of-body experience. On the other hand, this also means that the peak maximum of the temporoparietal cluster was strongly underestimated because of temporal averaging out.
We fully agree with Greyson et al. that one should be cautious about drawing analogies between an induced sense of disembodiment and spontaneous out-of-body experiences. However, because of the unpredictable and infrequent occurrence of spontaneous out-of-body experiences, it seems impossible to image them functionally with current technology in a scientific way. Our opinion is that it is highly likely that both induced and spontaneous experiences of disembodiment have common neuroanatomical circuits.
2 ReferencesDirk De Ridder, M.D., Ph.D.
University Hospital Antwerp, 2650 Edegem, Belgium
dirk.de. ridder@neurosurgery. be Koen Van Laere, M.D., Ph.D.
University Hospital Leuven, 3000 Leuven, BelgiumPaul van de Heyning, M.D., Ph.D.
University Hospital Antwerp, 2650 Edegem, Belgium1
Steinmetz H ,Furst G ,Freund HJ . Variation of perisylvian and calcarine anatomic landmarks within stereotaxic proportional coordinates. AJNR Am J Neuroradiol 1990;11:1123-1130
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Manola L ,Holsheimer J ,Veltink P ,Buitenweg JR . Anodal vs cathodal stimulation of motor cortex: a modeling study. Clin Neurophysiol 2007;118:464-474
CrossRef | Web of Science | Medline
