The incidence of unpleasant dreams after sub-anaesthetic ketamine

Ketamine is an N-methyl-D-aspartate (NMDA)receptor antagonist with psychotogenic effects and for whichthere are diverse reports of whether pleasant or unpleasantdreams result during anaesthesia, post-operatively or aftersub-anaesthetic use. The aim was to assess in healthy volunteers the incidence ofunpleasant dreams over the three nights after receiving asub-anaesthetic dose of ketamine, in comparison to placebo,and with retrospective home nightmare frequency as acovariate.Thirty healthy volunteers completed questionnairesabout retrospective home dream recall and were then giveneither ketamine or placebo. Ketamine resulted in significantly more meandream unpleasantness relative to placebo and caused athreefold increase in the odds ratio for the incidence of anunpleasant dream. The number of dreams reported over thethree nights did not differ between the groups. Theincidence of unpleasant dreams after ketamine use waspredicted by retrospectively assessed nightmare frequencyat home.Ketamine causes unpleasant dreams over thethree post-administration nights. This may be evidence of aresidual psychotogenic effect that is not found on standardself-report symptomatology measures or a result of disturbedsleep electrophysiology. The results have theoretical implications for the relationship between nightmares and schizotypy

From natural to sexual selection: Revealing a hidden preference for camouflage patterns

Abstract Natural and sexual selection can be in conflict in driving the evolution of sexual ornamentation. Sexual selection favours detectability to potential mates, whereas natural selection penalises detectability to avoid predators. Focusing on signal efficiency rather than detectability, however, suggests that natural and sexual selection need not be antagonistic. Considerable evidence demonstrates that people prefer images that match the statistics of natural scenes, likely because they are efficiently processed by the brain. This “processing bias” suggests that background-matching camouflage can be favoured by natural and sexual selection. We conducted an online experiment and showed for the first time human preference for camouflaged stimuli. Because the underlying visual mechanisms are shared across vertebrates, our results suggest that camouflage patterns could serve as evolutionary precursors of sexual signals