Developed in his (1999) book, The Feeling of What Happens, Antonio Damasio's three layeredtheory of consciousness is based on a hierarchy of stages, with each stage building upon the last. The most basic representation of the organism is referred to as the Protoself, next is Core Consciousness, and finally, Extended Consciousness. Damasio, who is an internationally recognized leader in neuroscience, was educated at the University of Lisbon and currently directs the University of Southern California Brain and Creativity Institute.^[1] Damasio's approach to explaining the development of consciousness relies on three notions: emotion, feeling, and feeling a feeling. Emotions are a collection of unconscious neural responses to qualia. These complex reactions to stimuli cause observable external changes in the organism. A feeling arises when the organism becomes aware of the changes it is experiencing as a result of external or internal stimuli.^[2]

Our most basic representation of self, as Damasio dubs it, is the Protoself. A non conscious state, this level of self is shared by many species. This is the most basic level of awareness signified by a collection of neural patterns that are representative of the body's internal state. The function of this 'self' is to constantly detect and record, moment by moment, the internal physical changes that affect the homeostasis of the organism.^[3] Protoself does not represent a traditional sense of self, rather, it is a pre-conscious state, which provides a reference for the core self and autobiographical self to build from. As Damasio puts it, "Protoself is a coherent collection of neural patterns, which map moment-by-moment the state of the physical structure of the organism" (Damasio 1999).^[2]

Multiple brain areas are required for the Protoself to function. Namely, the hypothalamus, which controls the general homeostasis of the organism, the brain stem, whose nuclei map body signals, and the insular cortex whose function is linked to emotion. These brain areas work together to keep up with the constant process of collecting neural patterns to map the current status of the body's responses to environmental changes. The Protoself does not require language in order to function, moreover it is a direct report of one's experience.

In this state, emotion begins to manifest itself as second-order neural patterns located in subcortical areas of the brain.^[2] Emotion acts as a neural object, from which a physical reaction can be drawn. This reaction causes the organism to become aware of the changes that are affecting it. From this realization, springs Damasio's notion of “feeling”. This occurs when the patterns contributing to emotion manifest as mental images, or brain movies. When the body is modified by these neural objects, the second layer of self emerges.^[2] This is known as core consciousness.

Sufficiently more evolved is the second layer of Damasio's theory, Core Consciousness. This emergent process occurs when an organism becomes consciously aware of feelings associated with changes occurring to its internal bodily state; it is able to recognize that his thoughts are his own, and that they are formulated in his own perspective.^[2] It develops a momentary sense of self, as the brain continuously builds representative images, based on communications received from the Protoself.^[2] This level of consciousness is not exclusive to human beings and remains consistent and stable throughout the lifetime of the organism^[4] The image is a result of mental patterns which are caused by an interaction with internal or external stimulus. A relationship is established, between the organism and the object it is observing as the brain continuously creates images to represent the organism's experience of qualia.

Damasio's definition of emotion is that of an unconscious reaction to any internal or external stimulus which activates neural patterns in the brain.^[2] ‘Feeling’ emerges as a still unconscious state which simply senses the changes affecting the Protoself due to the emotional state. These patterns develop into mental images, which then float into the organism's awareness. Put simply, consciousness is the feeling of knowing a feeling. When the organism becomes aware of the feeling that its bodily state (Protoself) is being affected by its experiences, or response to emotion, Core Consciousness is born. The brain continues to present nonverbal narrative sequence of images in the mind of the organism, based on its relationship to objects. An object in this context can be anything from a person, to a melody, to a neural image. Core consciousness is concerned only with the present moment, here and now. It does not require language or memory, nor can it reflect on past experiences or project itself into the future.

When consciousness moves beyond the here and now, Damasio's third and final layer emerges as Extended Consciousness. This level could not exist without its predecessors, and, unlike them, requires a vast use of conventional memory. Therefore, an injury to a person's memory center can cause damage to their extended consciousness, without hurting the other layers. The autobiographical self draws on memory of past experiences which involves use of higher thought.^[5] This autobiographical layer of self is developed gradually over time. Working memory is necessary for an extensive display of items to be recalled and referenced. Linguistic areas of the brain are activated to enhance the organism's experience, however, contrary to the language of thought hypothesis, language is not necessarily required.