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Ouch! That hurt

发布时间:2019-03-08 07:08:06来源:未知点击:

By Alison Motluk A FAMILY of neurons that respond specifically to pain have been identified by scientists in Canada. Intriguingly, a few of the neurons also react when a person is anticipating pain or is watching others in pain. Exactly how pain is perceived is still a mystery. But scientists believe that at least some neurons are responsible for recognising pain itself, not just excess sensation. William Hutchison and his colleagues at the Toronto Hospital recorded electrical signals from 68 neurons in 11 patients undergoing brain surgery. The patients, who had agreed to take part in the study, were fully awake and able to say if it hurt when the researchers started pinching and pricking them, and placing hot and cold plates on their skin. The researchers found that 11 of the 68 neurons responded specifically to pain while the others did not respond to pain at all. All of the pain responders were in a region deep inside the brain called the anterior cingulate cortex. Brain imaging studies and experiments on rabbits have already suggested this region might be involved in pain perception. But it seems that some neurons can differentiate between types of pain. Some of the 11 neurons responded when a plate on the patient’s forearm became uncomfortably cold, but didn’t react to pinpricks. Another neuron responded to pricks and jabs, but not to heat, cold and rough prodding and touching. Interestingly, this particular neuron fired again when the patient simply anticipated another prick. It also reacted when the patient watched the examiner prick his own finger. “These additional cognitive responses were a bit of a surprise,” says Hutchison. “There’s more going on than just an `ouch’ signal.” Many earlier studies have shown that single neurons can evoke very specific sensations such as the flavour of juice drunk as a child or the feeling of a tap on the shoulder. But stimulating the 11 pain neurons directly failed to produce any pain sensation. This suggests that these neurons are acting in concert with others. It could be that they have to be activated on both sides of the brain, or that activation in other regions of the cortex is necessary for pain perception, the researchers speculate in the current issue of Nature Neuroscience (vol 2, p 403). The result also suggests that the anterior cingulate plays a role in assimilating information about pain perception. Pain alerts us to danger, helps us evaluate how serious the danger might be and then helps us learn and remember to avoid it in future. The cingulate is heavily interconnected, with the amygdala, an emotional centre, and to many other regions, including those responsible for sensation,