"a blindfolded participant places the palm of their own hand on their forehead. The tendon of the muscle that straightens the elbow is vibrated at 70 Hz, which induces the illusion in the participant that they can feel their elbow bending, which in turn feels as although their hand is moving backwards through their own head."

Whereas the importance of sensory feedback for mental body representation is fairly well documented, there has until very recently not been any research addressing the questions of whether

"body image [can] be modified solely via internally generated mechanisms, and [whether] the principles that govern the relationship between body image and movement repertoire in the human brain [...] persist when the movement and body image is purely representative?"

In order to investigate these two questions, medical researchers Lorimer and Brugger again turned to experiments involving phantom limbs:

"Seven arm amputees with a vivid sense of their phantom arm, or an ‘‘intact body image'' of their phantom arm learned a particular arm movement that defied normal biomechanical constraints of the arm-thus it was an ‘‘impossible'' movement."

Participants were then required to fulfill a number of picture recognition tasks related to body image. In particular, these tasks relied on previous research that - interestingly enough by itself- demonstrates that the speed in which people are able to identify whether, let's say, a picture of a hand shows a left or a right hand, depends on the brain's body image; in the sense that it relates to the time it would require to (mentally) move one's own hand from whatever position it is currently in, to a posture that matches the one shown in the picture.
The left/right response task featured generally impossible hand postures; some of which were, however, possible to the modified phantom limb representations which participants had learned.
In analyzing the performance on this response task, the researchers were able to show

"decreased response times that were movement-specific, limb-specific, and image specific. Importantly, such a decrease was observed only in those participants who reported success at learning the impossible movement. Those people also reported profound shifts in the structural characteristics of their phantom arm."

Given that the imagined phantom limb does not send any proprioceptory feedback to the brain, this study reveals two important things:

"The first is that the feeling that we have of our own body, which constitutes a fundamental aspect of self-awareness, can be profoundly modified solely by internally generated mechanisms."

The second is an extension to the hypothesis that

"our movement repertoire and our anatomical structure are fundamentally linked [...] by demonstrating that this link governs, at a fundamental level, the representation of movement and the body in the human brain."

The authors add to this, by stating that

"In fact, this finding extends our understanding of the brain's plasticity because it is evidence that profound changes in the mental representation of the body can be induced purely by internal brain mechanisms-the brain truly does change itself."

Besides the intelligent experimental design, and the inherently interesting subject matter, the study allows for some speculation about the potential of mental body image exercises to help people with disrupted body images and motor problems, such as people suffering motor neglect after stroke, back pain, and complex regional pain syndrome, although I assume that the mirror-box treatment would likely always do a better job.

Main Reference:
Moseley GL, & Brugger P (2009). Interdependence of movement and anatomy persists when amputees learn a physiologically impossible movement of their phantom limb. Proceedings of the National Academy of Sciences of the United States of America, 106 (44), 18798-802 PMID: 19858475