In a scientific collaboration between the École
Polytechnique Fédérale de Lausanne (EPFL), Switzerland, and Scuola
Superiore Sant’Anna, Pisa, Italy, researchers combined virtual reality
and artificial tactile sensations to allow two people with amputations
to feel as though their prosthetic hands belonged to their bodies. The
results were published August 15 in the Journal of Neurology, Neurosurgery & Psychiatry. “The
brain regularly uses its senses to evaluate what belongs to the body
and what is external to the body. We showed exactly how vision and touch
can be combined to trick the amputee’s brain into feeling what it sees,
inducing embodiment of the prosthetic hand with an additional effect
that the phantom limb grows into the prosthetic one,” said Giulio
Rognini, PhD, from EPFL’s Laboratory of Cognitive Neuroprosthetics. “The
setup is portable and could one day be turned into a therapy to help
patients embody their prosthetic limb permanently.”
The
participants each had a left transradial amputation and were given
transverse intrafascicular multichannel electrode (TIMEs) implants. The
scientists provided artificial tactile sensations by stimulating nerves
in each participant’s residual limb that related to the tip of his index
finger. At the same time, the patient wore virtual reality goggles that
showed the index finger of the prosthetic limb glowing as the touch
sensations were administered.
Both patients reported feeling as
though their prosthetic hands belonged to their bodies. Moreover, when
asked to evaluate the position of their hands, both patients felt as
though their phantom limbs had extended into the prosthetic limbs.
Before the experiment, they reported that the phantom hand was small and
directly connected to the residual limb, as if the phantom limb had no
forearm, referred to as telescoping. During the experiment, they said
they felt their phantom limbs had extended and remained extended for up
to ten minutes afterwards.
The experiment required the patient to
passively observe two sensations on the fingertip, the visual glow and
the artificial touch happening in synchrony, in order for embodiment and
extension of the phantom limb to take place. EPFL says this is the
first time that the principles of multisensory integration, in
particular how the brain integrates bodily multisensory information to
create the coherent and compelling experience of having a body, have
been tailored to provoke embodiment of the prosthetic hand and reduction
of telescoping.
The study builds upon research led by EPFL that began in 2014,
in which scientists were able to provide real-time bidirectional
sensory perception to Dennis Aabo Sørensen, who also has a left
transradial amputation. In 2016, Sørensen was able to detect differences in texture by using the enhanced technology.
Editor’s note: This story was adapted from materials provided by École Polytechnique Fédérale de Lausanne.
