Subconscious Stimulus Recognition and Processing During Sleep

During sleep, consciousness is reduced, associated with a diminished connection of the brain to the environment. This is due to the blocking of the thalamocortical pathway by inhibitory mechanisms. This “thalamic gating” during sleep, however, is not complete, but partial. The stream of information is considerably reduced, but the brain is not fully disconnected from the environment. An inspection of the environment takes place to optimize safety during sleep. Stimuli having a meaning for the individual, or signaling danger, are recognized, and may enter into awareness, leading to a wake-up call, which allows the individual to react. This subconscious stimulus evaluation is regarded as having a guardian function for sleep. The recognition of stimuli during sleep points toward the presence of a sort of consciousness without awareness in the sleeping brain.