Out of Body Experience(OBE)

Olaf Blanke, Stphanie Ortigue, Theodor Landis and Margitta SeeckStimulating illusory own-body perceptions. Nature 2002, 419: 269-70.

Olaf Blanke and Shahar Arzy The Out-of-Body Experience: Disturbed Self-Processing at the Temporo-Parietal Junction The Neuroscientist 2005, 11: 16-24

Olaf Blanke, Christine Mohr, Christoph M. Michel, Alvaro Pascual-Leone, Peter Brugger, Margitta Seeck, Theodor Landis, and Gregor Thut Linking Out-of-Body Experience and Self Processing to Mental Own-Body Imagery at the Temporoparietal JunctionThe Journal of Neuroscience 2005, 25(3):550-557.

Irwin 1985:I was in bed and about to fall asleep when I had the distinct impression that I was at the ceiling level looking down at my body in the bed. I was very startled and frightened; immediately (afterwards) I felt that I was consciously back in the (body on the) bed again.

Etiology.

Blackmore (1982), Irwin (1985) OBE in 10% of healthy population in the majority of cultures of the worlds

Lippman (1953) OBE in two migraine patients

Green (1968) 11% of the OBE subjects that participated in her survey suffered from migraine headaches

Devinsky and others (1989) OBE in epilepsy patients: (non-lesional epilepsy / epilepsy due to an arteriovenous malformation / ewpilepsy due to posttraumatic brain damage)

Blanke and others (2002) induced by focal electrical stimulation

Blanke and others (2004) OBE due to a dysembryoplastic tumor one patient (case 3).

Stimulation delivered by subdural electrodes.

Purple: motor cortexGreen: somatosensoryBlue: auditory cortexYellow: OBEStars: epilepsy site

OBE is induced by electrical stimulation of temporoparietal junction (TPJ). Out-of-body and body-transformation experiences are transitory and may disappear when a person attempts to inspect the illusory body or body part.

Metzinger 2003 OBE is a threefold deviance from the normal self, because of 3 components below:

1-abnormal self unity: discrepancy between the place of self and body, between self and body is thus abnormal, because the self is not experienced as residing within the limits of one’s body.

2-abnormal self location: self is experienced to be in an abnormal place.

3-abnormal visuospatial perspective: the visuospatial perspective is no longer egocenteric.

Lesion location in out-of-body experience (OBE) patients. The MRI-based lesion overlap analysis of the three OBE patients from the study of Blanke et al (Brain-2004) is shown. The MRI of all patients was transformed into Talairach space and projected on the MRI of one patient. Each color rep-resents a different OBE patient. In two patients, the OBE site was located by intracranial electrodes during invasive presurgical epilepsy evaluation and in one patient by noninvasive methods for localizing the seizure-onset zone. Note the implication in all patients of the temporo-parietal junction.

The visual scene as a migraine patient experienced before a transient ischemic attack. experienced seeing it from his elevated position in the chair. Numbers indicate the dimensions of the patient's living room in meters. The position of the patient's wife is indicated by (A).

In various situations and various limb positions and various intensities of TPJ stimulation, a variety of illusions are perceived.

Vestibular sensations of of levitation and lightness accompanied OBE. The sense of gravity is lost and a 180 degree of rotation is experienced. Somatic and visual illusions about the body but no visual illusion with respect to extrapersonal space

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.

Brugger (2002) spontaneous OBEs rely on functional mechanisms similar to those used voluntarily during mental imagery with respect to one’s visuospatial perspective and body.

EEG Experimental design:

11 healthy people without OBE history were asked to make right–left judgments about a schematic human figure after having imagined themselves to be in the body position of the figure and to have its visuospatial perspective (OBT task). The left-right judgement was about which hand is wearing a glove. The judgments were made by button presses done as fast as possibleby index and middle fingers of subjects’ right hand. 123 channel evoked potential mapping was perfomred.

The schematic human figure could be facing toward or away from the volunteer. The volunteers’ transformation of their own bodies into the body position of the front-facing figures (as compared with the back-facing figures) mentally simulates the body position and the visuospatial perspective that is experienced during OBEs.

Control experiment: The same procedure but this time, the right-left judgment was made with respect to the computer screen. ISI=1000 ms, SOA=1220 ms, 3 blocks each of 80 trials, 20 of each one stimulus condition.

Results:

A, Reaction times in the OBT task (blue) and the lateralization task (red). On the left, the RTs (OBT task) are plotted separately for front-facing (light blue) and back-facing figures (dark blue). On the right, the RTs [lateralization task (LAT)] are plotted separately for front-facing (light red) and back-facing figures (dark red). Note the longer RTs for the OBT task. Front-facing figures during the OBT task, but not for the lateralization task, were characterized by longer RTs with respect to back-facing figures.

Results:

B, Segments of stable map topography in the four experimental conditions under the global field power curve from 0 to 700 ms. Evoked potential segment 6 (segment shown in black) was found from 330 to 400 ms and only in the OBT task.

C, Duration of evoked potential segment 6 (the respective map is shown in the right top corner of the figure) for the four experimental conditions for all participants. The duration of evoked potential segment 6 parallels the behavioral differences in the four experimental conditions.

* What about these peaks in OBT task that do no exist in lateralization task?

Results:

D, Evoked potential recorded at electrode P5 in the four experimental conditions showing differential coding between OBT (blue) and lateralization tasks (red) as well as between front-facing (light blue) and back-facing (dark blue) figures during the OBT task. The black bar estimates the time of differential coding between both tasks and is in agreement with the occurrence of evoked potential segment 6.

* What is the relation between the two plots of B and D? considering the point that from 0 to 250 ms, D has 3 turning points but B has 5.

Results:

E, LAURA(local auto-regressive average model) localized the voltage topography of segment 6 of figure B to the TPJ of both hemispheres with a predominant activation in the right hemisphere. Activation of the TPJ was found in 10 subjects and included both TPJs in four subjects, only the right TPJ in four subjects, and only the left TPJ in two subjects. In the 11th subject activation was found at the right temporooccipital junction).

TMS Experimental design:

7 healthy people (other than those previous 11)were asked to do the same OBT task. The control experiment was no longer like that of the previous experiment. The control experiment was the left-right judgment in an external object that was an F letter and people should make a left-right judgment about a dark square on the F. People were asked to rotate the object in their mind to the normal orientation and then make the judgment. This task is called Letter Transformation task (LT).

TMS was applied to TPJ as target and IPS (intraparietal sulcus) as control. IPS was chosen as a control site because it was not detected to be associated with OBT in EEG study, but it seems to be involved in mental rotation of objects (external objects by previous neuroimaging studies (Harris et al., 2000; Jordan et al., 2001; Gauthier et al., 2002; Podzebenko et al., 2002; Bestmann et al., 2002; Harris and Miniussi, 2003). TMS site was localized by MRI and coil position was determined by Brainsight.

TMS Experimental design:

TMS pulse was applied in 15 different SOAs in the range of 100-800 with respect to appearance of visual stimulus. Also there were some Baseline trials with no TMS discharge. Each of these 16 conditions were repeated for 8 times randomly ordered. TMS Intensity=75% maximal intensity (2.2 T).

Dependent variable: normalized RT

Subjects’ average RTs (of correct responses) in TMS trials were normalized to the corresponding baseline performance of the same condition (normalized RT value = RT with TMS –RT without TMS).

* Isn’t it more rational if we divide instead of subtracting?

Results:In baseline trials (no TMS applied), RTs were longer for front-facing human figures (723.7 58.9 ms; mean SE) and turned letters (668.9 52.4 ms) than for back-facing human figures (552.1 38.5 ms) and unturned letters (524.6 30.1 ms) (effect of stimulus orientation, F(1,6) 24.4; p 0.003). This suggests that the subjects engaged in mental rotations.

TMS over the TPJ in some certain SOAs interfered and delayed OBT taskin those trials that body rotation should be imagined.

This interference is selective for TPJ stimulation (relative to stimulation of a control site)

TPJ interference is task-specific, i.e., not observed for the LT task even those trials that need mental rotation

Note that TMS sometimes had a general facilitatory effect on RTs with respect to baseline performance , which was most pronounced for early TMS pulse delays (reflected in the negative values for normalized RTs). This general facilitatory effect also can be observed when a pure auditory signal is presented concomitant to task execution, is most likely to be unspecific to TMS and due to intersensory facilitation attributable to the coil click and tap when it discharges.

* I liked to also see the data of Error Rates. They have just showed that a TMS pulse, Interrupts and delays the procedures being done in TPJ. But I guess the more interesting thing is that after this interrupt, TPJ is able to resume the suspended procedure and the OBT task can still be done. This is how I like to see the ER data to see what is the likelihood of this resumption.