Why do phantom limbs occur

Post-stroke phantom limbs

Munich / Vienna - The perception of additional, non-existent limbs of the body is a condition that occurs again and again in people after a stroke. The Association of Neurologists reports on a particularly extreme example of these "phantom limbs" on the occasion of "Stroke Day". Since her recent stroke, one patient has been convinced that she has an extra third arm that she can feel, see and even move.

Blurred vision or even hallucinations

The imaging of this phenomenon showed how drastically brain damage can change body perception. "With every brain disorder such as a traumatic brain injury, stroke, tumor or circulatory disorder, visual disturbances can occur that express themselves like hallucinations," confirms Wilhelm Strubreither, chairman of the Society for Neuropsychology.

The patient, who felt a third arm, was examined using magnetic resonance imaging to obtain information about the brain activity. When trying to move the right, non-paralyzed hand, the motor region of the left hemisphere was correctly activated, while when trying to move the paralyzed left hand, the right hemisphere was active. If the woman wanted to move her phantom hand, the motor region was surprisingly also active - which proves the actual attempt at movement. No less astonishing was the activity in the visual center, which may explain why the woman could see her hand. She could also feel when she scratched her hand, since the corresponding brain regions for touch were also active.

While this case is a rare exception due to the parts of the brain that are also active for motor skills and touch and accordingly causes a stir, visual disturbances occur more often with brain damage. "The most common are disturbances of the basic functions such as blurred vision, problems with contrast vision or flashes and veils in the field of vision. Distortions, doubling as well as a smaller or larger view of the surroundings are also possible," explains Strubreither. In addition, there are also more complex forms in which patients see animals and people that are not present and perceive past events in repetition. In so-called Anton syndrome, people who are blind due to a cerebral infarction of the visual cortex of both hemispheres of the brain believe that they can see their surroundings. However, their descriptions are incorrect. "There are also patients who can no longer recognize objects or faces," says the neuropsychologist.

Special training brings relief

The cause of this misinterpretation of what is seen lies in the brain. "The connection between the halves of the brain or their fields of vision are disturbed, which can lead to these perceptual disorders," says Strubreither. There is no actual cure for most of these symptoms, but special training can at least partially improve visual perception. "With patients who can no longer recognize faces, one trains, for example, memorizing features that are supposed to facilitate identification. However, if the basic visual performance is disturbed, all that remains is compensation and explanation." (pte)