REM sleep and the development of context memory.

The paper proposes that REM sleep exists to promote the development of a special form of memory. This memory is a composite of many specific experiences in a particular environment. When it is subsequently invoked, it creates a contextual framework, thus it may be called context memory. The development of this kind of memory during waking is limited by the need to focus on salient or relevant experiences and restrict the processing of others. These restrictions include mechanisms that support orienting responses and selective attention to what is relevant. It is argued that during REM sleep, the reduction of noradrenergic activity undermines the restrictive effects of orienting and reduction of frontal lobe activity undermines bias toward relevant events. When their reduction is combined with a high level of cholinergic activity, many recent and associated memories may be activated and merged together, giving rise to some of the bizarre events experienced in dreams. Patterns of their activation can be transmitted to the hippocampus where they become integrated to form context memory. From this perspective, the need for REM sleep is greatest when the individual is most lacking in context memory at the beginning of life, although innate structures in precocious infants may lessen their reliance on the acquisition of context memory. Later in life, the need for REM may increase temporarily if the subject encounters a novel environment and is unprepared to meet its demands. However, REM sleep may also become unadaptive when it begins to perpetuate a context memory that has become infused with negative emotions experienced during depression.