Communication between the immune system and the brain also seems to go in the other direction: the brain can direct the immune system.
Some of these insights are decades old. In the 1970s, scientists conditioned rats to become immunosuppressed when they tasted saccharin, an artificial sweetener, by pairing it with an immunosuppressive drug for several days
15.
In more recent work, Asya Rolls, a neuroimmunologist at Technion — Israel Institute of Technology in Haifa, and her team explored the link between emotion, immunity and cancer in mice. They reported
16 in 2018 that activating neurons in the ventral tegmental area, a brain region involved in positive emotions and motivation, boosted the immune response and, in turn, slowed tumour growth.
Then, in 2021, her group pinpointed neurons in the insular cortex — a part of the brain involved in processing emotion and bodily sensations, among other things — that were active during inflammation in the colon, a condition also known as colitis.
By activating these neurons artificially, the researchers were able to reawaken the intestinal immune response
17. Just as Pavlov’s dogs learnt to associate the sound of a bell with food, causing the animals to salivate any time they heard the noise, these rodents’ neurons had captured a ‘memory’ of the immunological response that could be rebooted. “This showed that there is very intense crosstalk between neurons and immune cells,” says Movahedi, who wasn’t involved with this work.
Rolls suspects that organisms evolved such immunological ‘memories’ because they are advantageous, gearing up the immune system in situations when the body might meet pathogens. She adds that in certain cases, they can instead be maladaptive — when the body anticipates an infection and mounts an unnecessary immune response, causing collateral damage. This pathway might help to explain how psychological states can influence the immune response, providing a potential mechanism for many psychosomatic disorders, according to Rolls.
It could also inspire therapies. Rolls and her team found that blocking the activity of those inflammation-associated neurons lessened inflammation in mice with colitis. Her group hopes to translate these findings to humans, and is examining whether inhibiting activity using non-invasive brain stimulation can help to alleviate symptoms in people with Crohn’s disease and psoriasis — disorders that are mediated by the immune system. This work is in the early phases, Rolls says, “but it’ll be really cool if it works”.
