Australasian Science: Australia's authority on science since 1938

Dead Hands and Phantoms

Credit: iStockphoto

Credit: iStockphoto

By Lee Walsh, Janet Taylor and Simon Gandevia

Recent studies have highlighted how central signals in the brain can change our sensation of the position and movement of joints, and how phantom limbs form when sensory information is lost.

Lee Walsh completed his PhD on proprioception at Neuroscience Research Australia under the supervision of Janet Taylor and Simon Gandevia.

The full text of this article can be purchased from Informit.

You have probably woken at night occasionally with a “dead” hand or arm due to compression or stretching of the nerves going down your arm. The hand can be both paralysed (it won’t move when you try to move it) and anaesthetised (you can touch it with your other hand, but it feels numb and “dead”).

Logically you might expect to feel nothing – or the absence of an arm – when your brain receives no input from sensory nerves. Instead, you feel the presence of a real “dead” hand.

Similarly, you may have had dental anaesthesia. The anaesthetised tongue, jaw or lips again do not disappear, but remain in your consciousness, commonly feeling larger than usual.

What is going on? Awareness of a phantom body part develops rapidly and seamlessly in our brain without any cautionary clue that the brain has “created” something. It suggests that the brain maintains some representation of the body that does not rely on ongoing sensory input, so that a hand, for example, can be perceived despite the lack of sensory input from the hand to signal its existence.

The creation of a phantom happens in less common circumstances, such as when a limb has been amputated. The clinical descriptions of such cases are varied and even bizarre, probably because some nerves to the removed limb, or their central connections, are not completely “silent” or the nerves are...

The full text of this article can be purchased from Informit.