Pain is a complicated and distressing feeling that is understood by the brain when our nerves send signals to it. Just as our skin and muscles feel softness and warmth, so they feel pain too. By hurting, pain draws our attention to the affected area so that we don’t hurt ourselves further.
But, contrary to the age-old belief, scientists have found out that the brain too adds a layer of unpleasantness to pain, aggravating the condition.
A team of researchers from Stanford University found out the brain cells that are instrumental in making pain hurt more. While conducting the experiment on mice, they pinpointed the neurons in the mouse brain that make pain hurt. The scientists skillfully altered these neurons in a manner that reduced the agony of the pain without eliminating the sensation. The study, published in Science, is a conduit for future research into more targeted pain treatments.
It was a colossal challenge for Stanford University neuroscientist Grégory Scherrer, who co-led the study, to isolate the intertwisted neurons and deduce the ones that are associated with the pain. The team of researchers started the study with the amygdala, a slim, almond-shaped region in the brain known to regulate many emotions.
Scherrer collaborated with another neuroscientist Mark Schnitzer to create a miniature microscope that attaches easily to a mouse’s brain. This miniscope allowed the scientists to track the neurons of a normally behaving mouse’s brain. Then, they sent the slim scope across the brain to ascertain the flashing neurons as the mouse reacted to painful stimuli such as needle pricks.
The mouse reflexively withdrew when it felt pain. According to Scherrer, the reflexive behaviour indicates the sensation of pain that is not unpleasant. On the other hand, the mouse indicated the unpleasantness of the pain by starting to avoid painful stimulus or licking the paw that touched it. Scientists say that there is a constellation of about 150 neurons in the basolateral amygdala (BLA) that becomes active when the mouse feels pain. When the mouse feels more pain, this constellation in BLA glows brighter.
Further, to encode the extent of the unpleasantness of the pain, the research team turned off the pain neurons while the animal was in pain to detect any behavioural changes in it. Surprisingly, they found that the mice still experienced pain, but did not behave in a manner to show that it was unpleasant.
After a series of further experiments, scientists spotted the BLA neurons that play a crucial role in making the pain hurt. Both acute and chronic pain originate from these BLA pain neurons. Scientists, however, are looking to discover drugs to reduce the unpleasantness of pain using the BLA neurons. According to Scherrer, “Now that we know what neurons give pain its unpleasantness, we can look for receptors present only in those neurons, and not in other areas of the brain.”
These extraordinary receptors in the neurons make the pain chronic. Scientists are looking to design drugs to simmer them down. Furthermore, the areas of the brain that work in harmony with the BLA neurons to make the pain hurt are still unknown to the scientists. Scherrer and his colleagues are working to find out these connections to land a feasible conclusion.