Scientists have known for a long time that the gut communicated with the brain.
However, a distinction was often made between the conventional five senses of sight, hearing, touch, smell, and taste and the nutrient-sensing cells in the gut.
According to this way of understanding the nervous system, the gut only communicates with the brain slowly, using hormones it releases into the bloodstream. The other senses, however, communicate with the brain quickly and directly, in hundreds of milliseconds, using nerve pathways.
Still, new research has begun to talk about a gut sense. This is the sense of hunger or satiation felt as a result of cells in the linings in the gut that detect nutrients released from digesting food.
In 2018, researchers from Duke University showed that some of the gutâs sensory cells, called enteroendocrine cells, do more than release hormones. The cells also signal electrically, and form connections with nerve cells like other sensory cells do.
Using these connections they communicate directly with the brain on a millisecond timescale, just like the sensory cells in the eye or ear. They communicate via the vagus nerve, which runs from the brain to the organs of the body cavity.
The research is based on experiments done with mice, who have organs and nervous systems very similar to humans. In one experiment, they introduced a specially modified version of the rabies virus into their guts.
Since this virus can travel between cells, they used it to trace the nerve pathway from gut sensory cells to the brain. In another they showed that enteroendocrine cells could signal to a nerve when stimulated with nutrients.
Sources and Further Reading
- Haridy, R. Fast and hardwired: Gut-brain connection could lead to a "new sense." New Atlas, September 23, 2018.
- Kaelberer, M. M., et al. (2018). A gut-brain neural circuit for nutrient sensory transduction. Science. 361 (6408), eaat5236.