Dreaming: cognitive processes during cortical activation and high afferent thresholds.

The concepts of nonlocal, or distributed, cortical and cognitive activation are examined for their usefulness in describing the relations between sleep and waking neurocognitive processes. Changes in the pattern of distributed activation and inhibition of selected portions of sensory, cognitive, and motor decision modules account for the differences in imagery and thought across sleep and waking states in comparable environments. The massive inhibition of sensory and proprioceptive input to perceptual modules in Stage 1 REM sleep leaves the perceptual and cognitive modules, by default, with their own output as their sole input. Given this constraint, the activation of portions of the cortical structures that execute waking perceptual, cognitive and motor responses is necessary and sufficient to produce the imagery and thought of dreaming sleep. Connectionist models are introduced so that neurophysiological and cognitive concepts of distributed and local activation and inhibition can be translated into a common language, and in so doing, are used to simulate several processes fundamental to the production of imaginal thought and dreaming.