In the first account of how artificial limbs are represented in the brains of amputees, researchers have found the area of the visual cortex that recognizes hands can also identify prosthetic hands.

"While the use of a prosthesis can be very beneficial to people with one hand, most people with one hand prefer not to use one regularly, so understanding how they can be more user-friendly could be very valuable," said lead author Dr. Tamar Makin of the Institute of Cognitive Neuroscience, University College London (UCL).

"If we can convince a person's brain that the artificial limb is the person's real limb, we could make prostheses more comfortable and easier to use."

In order to understand if the brain could take advantage of resources (originally devoted to supporting hand functions) to represent prosthetics, researchers examined individuals who were born with one hand or lost their hand after birth. The study included 32 such people with one hand and 24 people with both hands, who were used as a control group. Neural responses of the participants were assessed through a functional MRI scan.

As part of the study — named "Artificial Limb Representation in Amputees" — participants were shown images of prosthetic limbs (pictures of their own prostheses were also included) and real limbs. Among the one-handed participants, hand-selective regions of the brain displayed a stronger response to images of prostheses, compared to the control group. This reaction was also observed when the image was that of a prosthetic that did not visually resemble a hand, such as a hook prosthesis. 

The response was particularly strong among those who used a prosthesis most frequently in their daily lives. Researchers found the regular use of prostheses was an important factor in the intensity of the response.

"Our findings suggest that the key determinant of whether the brain responds similarly to a prosthetic hand as it does to a real hand is prosthetic use. As many of our study participants lost their hand in adulthood, we find that our brains can adapt at any age, which goes against common theories that brain plasticity depends on development early in life," said Fiona van den Heiligenberg, the first author of the study who is also from the UCL Institute of Cognitive Neuroscience.

Previously, Heiligenberg had worked on a study titled "Adaptable Categorization of Hands and Tools in Prosthesis Users," which determined how one-handed people displayed more conceptual blurring between hands and tools due to their reliance on prostheses.

"The prosthesis is part of me, I don't regard it as an addition - I consider it a hand," explained one study participant named John Miller, who was born with only one hand and regularly used his prosthesis.

Clare Norton, another participant who had her hand amputated, also felt the more she used her prosthesis, the more she felt it becoming a part of her.

"Logically I know my prosthesis is not my missing hand - it's a tool, it's a new sensation and I accepted that," she said.