Cortical activation elicited by unrecognized stimuli

Background: It is unclear whether a stimulus that cannot be recognized consciously, could elicit a well-processed cognitive response. Methods: We used functional imaging to examine the pattern of cortical activation elicited by unrecognized stimuli during memory processing. Subjects were given a recognition task using recognizable and non-recognizable subliminal stimuli. Results: Unrecognized stimuli activated the cortical areas that are associated with retrieval attempt (left prefrontal), and novelty detection (left hippocampus). This indicates that the stimuli that were not consciously recognized, activated neural network associated with aspects of explicit memory processing. Conclusion: Results suggest that conscious recognition of stimuli is not necessary for activation of cognitive processing.