For longer versions of these and other stories from the
meeting, visit www.sciencenews.org/neuroscience2008
In their minds, volunteers swap
bodies with woman, mannequin
Illusion could help scientists study self-identity, body image
By Bruce Bower
It sounds like a lost episode of The
Twilight Zone. A man enters a laboratory,
dons a special headset and shakes hands
with a woman sitting across from him.
In a matter of seconds, he feels like he’s
inside the woman’s skin, reaching out
and grasping his own hand.
Strange as it sounds, neuroscientists
have induced this phenomenon in volunteers. People can experience the illusion that another body is their own, says
Valeria Petkova of the Karolinska Institute in Stockholm. She and Karolinska
colleague Henrik Ehrsson call the feeling
the “body-swap illusion.”
“Our subjects experienced this illusion
as being exciting and strange, and often
said that they wanted to come back and
try it again,” says Petkova, who reported
the findings.
Illusory body-swapping could provide
a new tool for studying self-identity and
psychiatric disorders that involve distortions of body image, she suggests. The
phenomenon might also be tapped to
enhance virtual reality experiences.
Volunteers in the body-swap experiments stood across from a male mannequin or a female experimenter and
received simultaneous visual and motor
input. A headset covering participants’
eyes displayed a 3-D view of the other
body’s visual perspective, transmitted
from a small camera on the other body’s
head.
In the mannequin situation, an experimenter simultaneously touched the participant’s belly and the mannequin’s belly
with separate probes. So, the volunteers
felt a poking in the abdomen but saw the
poking as if they were the mannequin. In
the real-person situation, participant and
experimenter shook hands. Thus, while
volunteers felt the sensation of hand
shaking, it appeared to them that they
were shaking their own hand. After 10 to
12 seconds of abdominal touch or handshaking, male and female participants
literally felt that they were in the mannequin’s or female experimenter’s body.
“In the body-swap illusion, we can see
that multisensory information powerfully affects the brain,” says Patrick
Haggard of University College London,
who was not part of the research team.
Petkova and Ehrsson first confirmed,
using questionnaires, that 16 male and
16 female volunteers experienced an
illusory body-swap with a mannequin.
Participants reported having had an
expectation that, if they moved, the mannequin’s body would move accordingly.
Then the researchers found that 10
volunteers experiencing a body-swap
with a mannequin displayed elevated
electrical responses in the skin on their
fingertips — a physiological indication of
heightened emotion — when a knife was
passed just over the mannequin’s arm.
In a third experiment, 12 volunteers
experiencing a body-swap with a female
experimenter exhibited comparable
physiological signs of emotional arousal
when a knife was passed just over the
experimenter’s arm.
When a researcher stroked a brush
along a volunteer’s arm, the illusion
vanished. In this way, each participant’s
personal sense of touch became disengaged from the other individual’s visual
perspective, Petkova proposes.
Morality askew in psychopaths
Psychopaths show neural responses
related to moral insensitivity and a keen
interest in moral violations, scientists
reported.
Researchers led by Kent Kiehl of
the University of New Mexico in Albuquerque recruited inmates from a New
Mexico prison to undergo brain scanning while viewing images that depicted
moral violations or images that contained no moral violations.
Functional MRI scans showed
reduced neural activity in 21 inmates
who qualified as psychopathic on
questionnaires, relative to 21 nonpsychopathic inmates, in brain regions
linked to attaching emotional meaning
to others’ acts and to reading others’
intentions, says study coauthor Alek
Chakroff, also of New Mexico. The
psychopaths identified moral pictures
and rated severity of moral infractions
as accurately as non-psychopaths, sug-
gesting the psychopaths intellectually
evaluated the situations without reacting emotionally, Chakroff adds.
Kiehl’s group also found that 25
psychopathic inmates displayed a
signature neural electrical response
a fraction of a second after viewing
images of moral violations, indicating
heightened attention to those images.
— Bruce Bower
Parasite twists rats’ innate fear
In a dangerous game of cat and
mouse, the most important player
turns out to be a parasite. Researchers know that the parasite Toxoplasma
gondii is a puppeteer that can force
a rat to go against its instincts and
become attracted to the scent of cat
urine. Now scientists have discovered
the regions of a specific part of the rat
brain called the amygdala involved in
this parasite-imposed death wish.
Toxo can only reproduce in the gut
of a cat, which poses a logistical nightmare for the rat-dwelling parasite. To
