A modified experiment with a rubber hand demonstrated the work of a sensory map of the space closest to the body.
The surface of our body and face on the postcentral gyrus of the cerebral cortex corresponds to a clear sensory map, groups of neurons that display what is happening with the hand, lower back or lips - a sensory homunculus. But the same map exists for the “periphery” space nearest to the body. She helps us handle objects and protects us - for example, picking up a pen from the table or instinctively dodging a random branch in the forest.
The final evidence for this came in the late 1990s in experiments on monkeys. Scientists from Michael Graziano's team have shown that certain neurons in the cortex are fired when an object appears in the region of space closest to the body. In addition, their stimulation caused the animals to instinctively deflect their head or limbs, as if taking them away from dangerous proximity.
Apparently, such a map of the periphery is also present in our brain. Original - albeit indirect - proof of this was presented by scientists at the Swedish Karolinska Institute, whose article was published in the journal Cognition. Henrik Ehrsson and his co-authors have demonstrated the emergence of an illusion that can be caused by a malfunction in the sensory map of the region of space closest to the body.
As a basis, psychologists took a classic experiment with a rubber hand, in which the subject sits at a table, hiding one hand behind a screen. At the same time, the same rubber hand lies on the table. The experimenter synchronously moves the brushes over both the real hand and the artificial one, at which the subject is looking. Quite quickly, he gets the feeling that the hand belongs to him.
Ersson's modified version of the experiment involved 101 volunteers. In general, everything happened exactly according to the classical scheme, with the exception that the experimenter did not touch the rubber hand with a brush, but drove it not high above it. The same movements were simultaneously performed for the subject's real hand, hidden behind the screen, although it was touched with a brush. As a result, the person felt a soft touch on the real hand, but saw a brush that moves directly above the rubber hand, about 10 cm.
Soon, the test subjects began to feel the rubber hand with their own, and in the space between it and the brush - the presence of a "magnetic force field" that elastically deflects its movements. But the most interesting were the circumstances under which the illusion disappears.
In particular, it is impossible to associate the observed movements with tactile sensations if the brush is carried away from the hand beyond 30–40 cm - apparently, beyond the limits of our peripheral space. It also does not arise if a metal barrier is placed between the brush and the hand: it cannot be dangerous, it cannot be taken by the hand, and the brush is as if "excluded" from the sensory map.
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