Conscious awareness differentially shapes analgesic and hyperalgesic pain responses.

A large proportion of human cognitive processes may operate outside of conscious awareness. Subliminally presented visual stimuli that are not consciously perceived have a pervasive effect on behavioral and autonomic responses. Recent studies have claimed that placebo/nocebo effects, which are previously thought to require conscious expectancies, can be elicited to comparable levels regardless of whether the stimuli were consciously perceived or not. We systematically explored the role of consciousness in conditioned analgesic and hyperalgesic pain responses using both classical delay conditioning procedure and trace conditioning procedure. In 2 experiments (total N = 247), we found that analgesic and hyperalgesic responses were differentially dependent on the conscious awareness of the relevant stimuli. Specifically, the analgesic response was only significant when stimuli were supraliminal in both conditioning/acquisition phase and test/activation phases. While the hyperalgesic responses were acquired and activated irrespective of stimulus exposure (supraliminal/subliminal), the magnitude of this response was larger when stimuli were supraliminal in the test stage. Our results indicate that analgesic responses require both conscious conditioning and conscious activation, challenging the view that classical conditioning of analgesic pain responses operates without conscious awareness. Hyperalgesic responses are generally not dependent on the consciousness of stimuli, suggesting the presence of a valence-specific rapid regulatory mechanism to enable adaptive responses in threatening circumstances. Our study demonstrates a nascent role of consciousness in the learning of complex cognitive processes.