Priming recognition in good sleepers and insomniacs

Objectives: Although insomniacs often complain of memory difficulties, there is no consistent evidence of objective memory impairment. Furthermore, while the majority of the studies addressed explicit memory, only few studies investigated implicit memory; in particular, very little is known concerning other types of implicit memory besides the procedural one, such as priming. The aim of the study was to investigate priming effect for visual stimuli in insomniacs. Methods: Twenty-three insomniacs and 20 good sleepers performed a visual priming task in which they were asked to name new and old pictures presented at nine ascending levels of spatial filtering. Both neutral and sleep related stimuli were used in the priming task, since previous research showed an attentional bias for sleep-related stimuli. Results: The priming effect was observed in both groups, suggesting that disturbed sleep does not affect this type of implicit memory. However, identification process in insomniacs is influenced by the nature of the stimulus to identify: insomniacs recognized both new and old sleep-related stimuli at lower spatial frequency compared to good sleepers. Conclusions: The tendency to attend selectively to sleep-related stimuli may influence top-down processes occurring during identifi- cation of filtering stimuli, determining a pre-allocation of attentional resources and facilitating identification process in the presence of scant physical information. The presence of different identification processes for sleep-related stimuli compared to neutral ones in poor sleepers who do not yet meet diagnostic criteria for insomnia, could be a “preclinical signal” to identify those subjects, among poor sleepers, most likely to develop insomnia.