Warp factor one


By Nell Boyce ZAP the back of the head with an electromagnet and people reach for the place where something was, rather than where it has moved to, say a team of neurologists. They say this shows that the brain plans movements in advance—and that the part they zapped constantly updates these plans. Evidence from stroke victims and brain imaging experiments suggests that three separate areas of the brain—the parietal cortex, the premotor cortex and the cerebellum—somehow work together to plan and execute movements. However, their precise roles are controversial (“The hand in your head”, New Scientist, 8 May, p 42). Scott Grafton and his colleagues at Emory University School of Medicine in Atlanta looked at the role of the posterior parietal cortex. They asked volunteers to point to a light hovering in darkness. As they reached out, the researchers moved the target slightly, causing the volunteers to compensate subconsciously, so their hands pointed at the light’s new position. The researchers then used transcranial magnetic stimulation to disrupt electrical activity in the posterior parietal cortex just as the volunteers’ hands began to move. When this happened, they pointed to the light’s original position rather than to its new one. The magnetic stimulation had no effect on their ability to touch stationary targets. (Nature Neuroscience, vol 2, p 563). “It really provides strong evidence that we plan in advance,” says Grafton,
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