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Brain uses eyes to pick up things

31 August 2010 NWO (Netherlands Organization for Scientific Research)

How does your brain know where your hand has to go to pick up a cup of coffee and successfully bring this to your mouth? By converting all of the information into coordinates of the eye discovered Dutch researcher Sabine Beurze. Unravelling those calculations will make it possible to more accurately control arm prostheses.

Babies learn to pick things up or put things down without knocking everything over. How the brain combines information about the position of your arms with the information that comes in through your eyes was largely unknown. Beurze allowed study subjects to perform tests in an MRI scanner. These revealed that our brains convert all of the information into a single calculation system: that of our eyes.

Pointing in the dark

Tied up in the dark with only your forearms and hands still free. Your head is so firmly fixed that it is impossible for you to move it. What do you need to do? Point to small lights. That was the task Beurze gave her study subjects. They could not see their hands and so they had to determine where to move them based on the information from muscles and nerves in the body. Meanwhile the researcher recorded the activity in the brain. Two regions in the brain were found to be involved in the movement: the posterior parietal cortex and the dorsal premotor cortex. The brain uses the same regions for the planning of eye movements.

To examine how the brain processes the incoming information from the eyes, muscles and nerves, Beurze devised another test. Study subjects had to stretch out their arm and on command point this ten degrees to the right. They had to do this with their arm stretched out in front of them and with their arm to the right. Sometimes the study subjects could look at their hand and on other occasions not. The mistakes study subjects made demonstrated that even if they could not see their hand, the brain calculated where their hand was in relation to their eye. By doing this the brain eventually obtains a reference framework for the position of the hand in relation to the target.

Arm prosthesis

Sabine Beurze examined for the first time how people convert different information flows into a system to control movement. Up until now, most of the research had been done on apes. The results of Beurze’s research might contribute to an improved control of arm prostheses. Although prostheses that can be controlled by the brain are currently under development, these are still prone to errors. Understanding which calculations the brain performs to control movement will make it possible to further perfect these arm prostheses. The results also provide hope for people with a motor impairment.

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