Rapid-eye-movement sleep involves the memory-conversion circuits in a brain model

People can remember the content of a dream in rapid eye movement (REM) slee p but cannot do so in slow-wave sleep. According to a brain model, memory i s stored in encoding synapses as presynaptic axonal 'on-off' patterns and m odulating synapses help encoding synapses convert short-term memory into lo ng-term memory. These lead to the hypothesis that REM sleep involves modula ting synapses of the memory-conversion circuits including the anterior nucl ei and dorsomedial nuclei of the thalamus. Cortical neurons get more rest i n slow-wave sleep than in REM sleep. The locus coeruleus, raphe nuclei, and tuberomammillary nuclei get more rest during REM sleep when these nuclei c ease to fire. The paralyses of peripheral muscles during REM sleep and cata plexy, and cessation of chorea, athetosis, hemiballismus, and parkinsonism tremor during sleep may result from spinal cord inhibition by the gigantoce llular nuclei and raphe nuclei at the reticular formation. Sleep and wake r elate to the light-dark cycle on the Earth. Were the light-dark cycle 50 ho urs a day, the human circadian clock might be around 50 hours. With increas ing use of artificial light to keep people awake at night, it may affect th e circadian rhythm and firing rate of neurons, the presynaptic axonal 'on-o ff' patterns as content of consciousness, and the mood. (C) 2000 Harcourt P ublishers Ltd.