Nature, published online: 09 December 2004
Roxanne Khamsi
Doubt cast on theory that magnetic fields spark religious feelings.
Studies showing that magnetic stimulation of the brain induces spiritual experiences are being queried by researchers who cannot reproduce key results. If the traditional theory is wrong, scientists will be left struggling to explain how such thoughts and sensations are generated.
In the past, scientists have claimed that religious or out-of-body experiences result from excessive bursts of electrical activity in the brain. In the 1980s, Michael Persinger, a neuroscientist at the Laurentian University in Ontario, Canada, began exploring this idea through a series of experiments.
Participants wore helmets that targeted their temporal lobes with weak magnetic fields, of roughly the same strength as those generated by a computer monitor. Persinger found that this caused 80% of the people he tested to feel an unexplained presence in the room. Persinger suggested that magnetism causes bursts of electrical activity in the temporal lobes of the brain, and he linked this to the spiritual experiences.
Blinding science
A group of Swedish researchers has now repeated the work, but they say their study involves one crucial difference. They ensured that neither the participants nor the experimenters interacting with them had any idea who was being exposed to the magnetic fields, a 'double-blind' protocol. Without such a safeguard, "people in the experimental group who are highly suggestible would pick up on cues from the experimenter and they would be more likely to have these types of experiences," says Pehr Granqvist of Uppsala University, who led the research team. Beyond the double-blind aspect, Granqvist says the nuts and bolts of the experiment mirrored those conducted in the past. He and his colleagues tested 43 undergraduate students by exposing them to magnetic fields that ranged from 3 to 7 microtesla and were aimed just above and in front of the ears, to target the temporal lobes. They also tested a control group of 46 volunteers who wore the helmet but were not exposed to the magnetic field. The volunteers were then asked to complete questionnaires about what they experienced during each session. The researchers report their results online in Neuroscience Letters1.
Strong spirits
In contrast to the results from Persinger and others, the team found that the magnetism had no discernable effects. Two out of the three participants in the Swedish study that reported strong spiritual experiences during the study belonged to the control group, as did 11 out of the 22 who reported subtle experiences.
Granqvist acknowledges that this seems to be quite a high level of spiritual experiences overall, but says that it matches the level that Persinger saw in his control groups.
The researchers say they do not know what neurological mechanism could be generating the experiences. However, using personality tests they did find that people with an orientation toward unorthodox spirituality were more likely to feel a supernatural presence, as were those who were, in general, more suggestible.
Field defence
Persinger, however, takes issue with the Swedish attempts to replicate his work. "They didn't replicate it, not even close," he says. He argues that the Swedish group did not expose the subjects to magnetic fields for long enough to produce an effect. He also stresses that some of his studies were double-blinded. Although the experimenters knew when the magnetic field was being applied, he says that they did not know what effect the field was expected to induce.
Susan Blackmore, a psychologist based in Bristol, UK, is also reluctant to give up on the theory just yet. She has firsthand experience of Persinger's methods. "When I went to Persinger's lab and underwent his procedures I had the most extraordinary experiences I've ever had," she says. "I'll be surprised if it turns out to be a placebo effect."
She too thinks that the Swedish researchers may have used magnetic fields that varied subtly from those of Persinger. "But double-blind experiments will ultimately give us the final answer," she says.
Roxanne Khamsi
Doubt cast on theory that magnetic fields spark religious feelings.
Studies showing that magnetic stimulation of the brain induces spiritual experiences are being queried by researchers who cannot reproduce key results. If the traditional theory is wrong, scientists will be left struggling to explain how such thoughts and sensations are generated.
In the past, scientists have claimed that religious or out-of-body experiences result from excessive bursts of electrical activity in the brain. In the 1980s, Michael Persinger, a neuroscientist at the Laurentian University in Ontario, Canada, began exploring this idea through a series of experiments.
Participants wore helmets that targeted their temporal lobes with weak magnetic fields, of roughly the same strength as those generated by a computer monitor. Persinger found that this caused 80% of the people he tested to feel an unexplained presence in the room. Persinger suggested that magnetism causes bursts of electrical activity in the temporal lobes of the brain, and he linked this to the spiritual experiences.
Blinding science
A group of Swedish researchers has now repeated the work, but they say their study involves one crucial difference. They ensured that neither the participants nor the experimenters interacting with them had any idea who was being exposed to the magnetic fields, a 'double-blind' protocol. Without such a safeguard, "people in the experimental group who are highly suggestible would pick up on cues from the experimenter and they would be more likely to have these types of experiences," says Pehr Granqvist of Uppsala University, who led the research team. Beyond the double-blind aspect, Granqvist says the nuts and bolts of the experiment mirrored those conducted in the past. He and his colleagues tested 43 undergraduate students by exposing them to magnetic fields that ranged from 3 to 7 microtesla and were aimed just above and in front of the ears, to target the temporal lobes. They also tested a control group of 46 volunteers who wore the helmet but were not exposed to the magnetic field. The volunteers were then asked to complete questionnaires about what they experienced during each session. The researchers report their results online in Neuroscience Letters1.
Strong spirits
In contrast to the results from Persinger and others, the team found that the magnetism had no discernable effects. Two out of the three participants in the Swedish study that reported strong spiritual experiences during the study belonged to the control group, as did 11 out of the 22 who reported subtle experiences.
Granqvist acknowledges that this seems to be quite a high level of spiritual experiences overall, but says that it matches the level that Persinger saw in his control groups.
The researchers say they do not know what neurological mechanism could be generating the experiences. However, using personality tests they did find that people with an orientation toward unorthodox spirituality were more likely to feel a supernatural presence, as were those who were, in general, more suggestible.
Field defence
Persinger, however, takes issue with the Swedish attempts to replicate his work. "They didn't replicate it, not even close," he says. He argues that the Swedish group did not expose the subjects to magnetic fields for long enough to produce an effect. He also stresses that some of his studies were double-blinded. Although the experimenters knew when the magnetic field was being applied, he says that they did not know what effect the field was expected to induce.
Susan Blackmore, a psychologist based in Bristol, UK, is also reluctant to give up on the theory just yet. She has firsthand experience of Persinger's methods. "When I went to Persinger's lab and underwent his procedures I had the most extraordinary experiences I've ever had," she says. "I'll be surprised if it turns out to be a placebo effect."
She too thinks that the Swedish researchers may have used magnetic fields that varied subtly from those of Persinger. "But double-blind experiments will ultimately give us the final answer," she says.
References
1. Granqvist P., et al. Neurosci. Lett., published online
doi:10.1016/j.neulet.2004.10.057 (2004).
Cette étude vient contredire les résultats d’une étude précédente. Une fois de plus, l’absence du double aveugle et probablement le petit nombre de sujets et de tests expliquent ces controverses.
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