First of all, one has to become familiar with Damasio's terminology. Damasio distinguishes feelings and emotions: a feeling is a mental representation of the state of the organism's body, the perception of body state, whereas an emotion is the reaction to a stimulus and the associated behavior (e.g., a facial expression). So the feeling is the recognition that an event is taking place, whereas the emotion is the visible effect of it. Emotions are bodily things, while feelings are mental things. Emotions are an automatic response. They don't require any thinking. They are the fundamental mechanism for the regulation of life. Emotions precede feelings, and are the foundations for feelings.

Evolution has prepared us with a repertory of emotions that we apply to the circumstances (somehow we pick an emotion to "react to" a circumstance the same way we pick an antibody to fight a virus). The effect of the emotion is both some bodily behavior and the creation of a neural map. That neural map leads to the feeling, and the relationship between maps and feelings is that feelings reflect how well the body is doing according to the map. Neural maps of body states are useful to manage the body. Feelings allow us to reason about the cause of the emotion. Feelings allow us to see the big picture, not just to react mechanically to a situation.

Basically neither Damasio's feeling nor Damasio's emotion are what we call "feeling" and "emotion". They are only two physical components (possibly side-effects) of what we normally refer to as a "feeling" or an "emotion". But Damasio states that his feelings enter the mental realm, whereas his emotions don't. So his emotions are more "physical' that his feelings (emotions are neural processes that recognize and react to a situation, feelings are maps in the brain that represent the body state).

An emotion is registered by the brain when a stimulus is recognized as useful for survival or for well-being or damaging for survival and well-being. This appraisal results in bodily changes, such as quickening heart-beat, tensing muscles, etc. These bodily changes also imply that a map changes in the brain, and this change is the physical implementation of the "feeling".

The best part of Damasio's theory is probably that he finds an analogy between the emotional system and the immune system. The immune system produces antibodies to fight invading viruses; or, better, the invading virus selects the appropriate antibody. An emotional response is basically the antibody that reacts to an invading stimulus, that is selected by that stimulus.

Damasio also sketches the brain regions that account for emotions: the amygdala is at the center of the triggering event and the hypothalamus is at the center of the execution.

Damasio claims that feelings help us solve complex problems. This may seem absurd, as my "feeling" of fear helps me solve very simple problems (e.g., do not cross a freeway on foot during rush hour), but you have to remember that Damasio's "feeling" is not a feeling, it is a lasting memory of an emotion. Then you understand why he claims that feelings help manage life in the long-term. And you understand why he claims, like Spinoza, that the mind is simply an idea of the body. So, for example, joy is the idea of equilibrium: "optimal physical coordination".

First came the machinery for emotions (reacting to a stimulus), and then the machinery for feelings (the brain map). Feelings prolong the effect of an emotion because they affect memory.

According to this theory, all living organisms have "proto-selves". However, only organisms with a complex nervous system capable of "seeing" their proto-self interacting with the world also have real "consciousness". These organisms are capable of registering the "feeling of what happens". Human consciousness is one further step beyond, enabled by the fact that we have a large memory that allows autobiographical memory.

Damasio does not even try to explain where feelings (my feelings) and consciousness come from. He is merely a neurologist analyzing the way the emotional system works.

If the mind is an idea of the body, the self is an idea of ideas. The self groups all the ideas of the body and generates a sense of unity.

The problem is that Damasio's theory does not explain well the most common emotions/feelings of our ordinary lives. Our state of happiness or sadness is often due to factors external to our body. I can easily recover from the momentary pain caused by hurting my finger or my biting my tongue, but it takes months to recover from a divorce or a monetary loss. Let's say that tomorrow they announce you won a million dollars at the lottery: there has not been a significant change in the state of your body, but you suddenly become very, very happy. That happiness is not due to a change in the state of your body, but to a change to your circumstances. If your mother is gravely ill, you are sad: that, too, has no direct impact on the organs and limbs of your body, and therefore on the body's representation in the brain. But you can be very sad for many many months. It is hard to think of any physical change that has the same long-lasting impact that circumstances can have on an individual's emotional life.

There is something fundamental that is missing in Damasio's theory: that I represent the world (the world, not my body) and become sad or happy based on that representation. It is the representation of the world (e.g., the horrors of Rwanda) that make me sad, not the representation of the state of my body. So emotions are not due (only) to representations of the body. So the mind is not the same substance as the body. Damasio concludes that the mind is the body. If one followed Damasio's reasoning, one would rather reach the intriguing conclusion that "the mind is the world", because the mind comes from a representation of what is going on in the world.

Damasio extends his discussion to the spiritual realm, a rarity in neuroscience. But, alas, his conclusions are scary, to say the least. A "spiritual feeling" is, for him, quite simply a state of maximum harmony, the "feeling" that everything is under control in the organism. Since I have never experienced a "spiritual feeling", I guess that means that my organism is completely screwed up. On the other hand, the many Islamic and Christian fundamentalists who became mass killers and claimed to have strong spiritual feelings were blessed, according to Damasio's definition, with a brain that was working perfectly well.