Working in Movement

Maps help you get where you want to go. But an inaccurate map is even less useful than last week's newspaper, though you can still wrap fish with both of them, I suppose.

You wouldn't think your own body would rely on a map for its everyday goings on, but there's lots of research pointing to sensory and motor activity linked to their representations in the brain. That's kind of like a map. But there can be problems when those maps become inaccurate or otherwise faulty.

Most brain representations get information from specialized types of sensors or receptors in the muscles, skin and joints. There are sensors that feed direct experiences of touch, position in space, or pain. But, as reported on in Experiment Gives Illusion of That Shrinking Feeling there seem to be no such receptors dedicated to sensing the size of body parts. (Another report is in Feeling fat can be 'in the mind').

Like Alice in Wonderland, participants in a study at University College of London felt themselves shrinking. However, it was their waist size getting smaller, and not their entire bodies shrinking . But it wasn't due to the tea they had drunk. Their own brains were fooling them into experiencing a sensation that wasn't actually occurring.

Researchers produced this effect in most of the 17 participants by stimulating tendons in the wrists, while the hands were on the waist. The wrists moved from the stimulation, but the hands didn't. Most participants felt their waists shrinking, some by as much as 28%. An earlier study had participants feel their noses as the wrists were stimulated, producing a Pinoccio-like effect of their noses growing.

The sensation of growing noses and shrinking waists was due to a conflict between the senses;

"The illusion happens as a result of a conflict between senses," (lead researcher Dr. H. Henrik) Ehrsson said, explaining that the wrists feel as if they are moving, but the palms of the hands, resting against the waist, do not. "The brain has to interpret the conflicting sensory information. The brain hates ambiguity. It always tries to come up with an explanation."

Brain imaging done at the time indicated activity in an area of the brain concerned with processing sensory information, the parietal lobe. The more shrinkage felt, the higher the parietal activity.

Damage to this area can result in misleading maps. According to Dr. Ehrsson,

... other studies have shown that people with injuries in the parietal cortex area of the brain experience the feeling that the size and shape of their body parts have changed.

There is much more to be explored about this idea of faulty brain representations of sensory-motor and other types of activity. Just ask Alice.