Understanding how the human brain processes its desire to move, before the actual movement command is issued for the muscles, has been a long-term impossibility for neuroscientists, mostly because of the difficulties they've experienced in determining which areas of the cortex are involved in the process. Only recently, experts from the University of Lyon (UL) in France have found a way around this obstacle, by designing an experiment that artificially stimulates brain regions to feel like they want to perform a certain action.
Results of the scans, performed on the brains of fully conscious people, revealed that the cortex area involved in the desire to move was different from that in charge of actually issuing the command. For a long time, brain experts have known that humans control actions by subjecting them to desires and plans, but how exactly people generate these intentions, also known as volition, has remained a mystery for quite some time.
UL Neuropsychologist Michel Desmurget, the leader of the French research team, wrote in the May 7th issue of the journal Science that intention was processed and integrated inside the parietal cortex, whereas the region that actually triggered the movement was the premotor cortex.
During previous studies, brain experts became aware of the fact that the parietal cortex might be involved with this process, but had no way of saying that for sure. In past instances, they told test subjects to generate an intention to move, while they recorded the activity in the brain using external sensors.
But the results were inconclusive, because the brain was differently hardwired when it came to fulfilling an outside command, or performing an action of its own accord. University College London (UCL ) Cognitive Neuroscientist Patrick Haggard explained this by saying that, “When we instruct our subjects to generate internally an intention to move – that in itself could, in fact, be an external signal.”
For the new experiment, the French experts carried out direct tests on seven volunteers, who were undergoing surgeries to have tumors in their brains removed. During the operations, their brains were directly stimulated with a low-intensity electrical current, and electric charges in several of their muscle groups were recorded at the same time. They were then asked when they felt the need to move, and when they felt like they had actually moved.
The scientists stimulated many zones in the brain, but, when they reached the parietal cortex, they got the most clear confirmation. If a low current was applied, patients reported the need to move, whereas, if the intensity was stepped up a notch, the participants said that they felt like they had already moved. Conversely, when the premotor cortex was stimulated, the patients moved, sometimes a lot, without knowing that they had done so. This type of experiment “provides an exciting way to study an experience that comes so close to what it means to be a human being,” Haggard added, as quoted by Nature.