Although research has investigated the feasibility of establishing classica
lly conditioned physiological responses during sleep, very few experimental
studies have considered whether classically conditioned cognitive associat
ions are possible. Since dreams have previously been described as a state o
f "hyper-association," an experiment involving classical conditioning of th
e human salivary response and associated dream content was conducted. Durin
g wakefulness, repeated pairings of a conditioned stimulus (CS; a red light
) with an unconditioned stimulus (UCS; citrus juice) yielded a conditio aut
onomic response (CR; salivation) on presentation of the CS alone. After exp
osure to the CS during REM sleep, salivary excretion rates measured upon aw
akening were significantly higher than measures taken from baseline REM awa
kenings. However, no CR-related dreams were reported by the participants. T
his result could be interpreted as evidence that participants in this exper
iment did not experience higher-order memory associations to the external s
timuli presented during REM. Alternatively, the lack of CR-related dreams c
ould be explained by previous findings that the autonomic nervous system of
ten works independently of higher-order cognitive activity. Therefore, if a
n autonomic association is formed, this does not necessarily imply a cognit
ive one.