Primary consciousness is a term the American biologist Gerald Edelman coined to describe the ability, found in humans and some animals, to integrate observed events with memory to create an awareness of the present and immediate past of the world around them. This form of consciousness is also sometimes called "sensory consciousness". Put another way, primary consciousness is the presence of various subjective sensory contents of consciousness such as sensations, perceptions, and mental images. For example, primary consciousness includes a person's experience of the blueness of the ocean, a bird's song, and the feeling of pain. Thus, primary consciousness refers to being mentally aware of things in the world in the present without any sense of past and future; it is composed of mental images bound to a time around the measurable present.

Conversely, higher order consciousness can be described as being "conscious of being conscious"; it includes reflective thought, a concept of the past, and speculation about the future.

Primary consciousness can be subdivided into two forms, focal awareness and peripheral awareness. Focal awareness encompasses the center of attention, whereas peripheral awareness consists of things outside the center of attention, which a person or animal is only dimly aware of.

One prominent theory for the neurophysiological basis of primary consciousness was proposed by Gerald Edelman. This theory of consciousness is premised upon three major assumptions:

Edelman's theory focuses on two nervous system organizations: the brainstem and limbic systems on one side and the thalamus and cerebral cortex on the other side. The brain stem and limbic system take care of essential body functioning and survival, while the thalamocortical system receives signals from sensory receptors and sends out signals to voluntary muscles such as those of the arms and legs. The theory asserts that the connection of these two systems during evolution helped animals learn adaptive behaviors. This connection allows past signals related to values set by the limbic-brain stem system and categorized signals from the outside world to be correlated, resulting in memory in conceptual areas. This memory is then linked to the organism's current perception, which results in an awareness of the present, or primary consciousness. In other words, Edelman posits that primary consciousness arises from the correlation of conceptual memory to a set of ongoing perceptual categorizations—a "remembered present".

Other scientists have argued against Edelman's theory, instead suggesting that primary consciousness might have emerged with the basic vegetative systems of the brain. That is, the evolutionary origin might have come from sensations and primal emotions arising from sensors and receptors, both internal and surface, signaling that the well-being of the creature was immediately threatened—for example, hunger for air, thirst, hunger, pain, and extreme temperature change. This is based on neurological data showing the thalamic, hippocampal, orbitofrontal, insula, and midbrain sites are the key to consciousness of thirst.

These scientists also point out that the cortex might not be as important to primary consciousness as some neuroscientists have believed. Evidence of this lies in the fact that studies show that systematically disabling parts of the cortex in animals does not remove consciousness. Another study found that children born without a cortex are conscious. Instead of cortical mechanisms, these scientists emphasize brainstem mechanisms as essential to consciousness. Still, these scientists concede that higher order consciousness does involve the cortex and complex communication between different areas of the brain.

Physiologically, three fundamental facts stand out about primary consciousness: