4 ideas
When a person considers an option, the brain reactivates the bodily state that was paired with similar outcomes in the past, producing a gut feeling that is either unpleasant or appealing. This marker quickly rules options out or pushes them forward before any explicit cost-benefit analysis starts. As a result, deliberate reasoning only has to work through a small, pre-screened set of options rather than an unmanageable number of possibilities.
In 1848 an iron tamping rod passed through the frontal lobes of railroad foreman Phineas Gage. He survived with his speech, memory, and intelligence intact, but he went from being responsible and well regarded to being profane, impulsive, and unable to follow through on plans. The case shows that damage to a specific brain region can destroy social and practical judgment while leaving general cognitive ability untouched.
A feeling is the brain's perception of changes in the body's own state, such as heart rate, gut tension, and muscle tone, together with the thoughts occurring at the same time. From this view, the mind is continuously monitoring the body, and a person's sense of self is built on that ongoing monitoring. Neither mind nor self is a separate thinking substance that only happens to be attached to a body.
Somatic markers can arise in two ways. In the body loop, the body actually changes and the brain senses that change. In the as-if loop, the brain simulates the expected bodily state internally without the body changing. The as-if loop allows fast, cheap emotional evaluation of imagined scenarios, and repeated experience of real bodily responses is what trains those simulations.