Effects of different subanaesthetic doses of (S)-ketamine on psychopathology and binocular depth inversion in man

The role of the N-methyl-D-aspartate (NMDA) neurotransmitter system in relation to psychoses is not completely understood, but represent a challenge in neurobiological research. The psychotic states induced by NMDA antagonists such as phencyclidine and ketamine have been described as being most similar to schizophrenia and the NMDA system has been implicated in the pathogenesis of schizophrenia. Binocular depth inversion, an illusion of visual perception, has been shown to be impaired in psychotic and psychotomimetic states in healthy and schizophrenic subjects. In this study, pictures of natural and artificial objects were presented stereoscopically to 12 healthy male volunteers and depth perception assessed using an operationalized method. The effects of the psychotomimetic S-enantiomer of the anaesthetic ketamine in two different subanaesthetic doses were compared with those of a placebo. In spite of dose dependence and grave subjective and significant objective psychopathology, no significant impairment of binocular depth perception was found with (S)-ketamine. Implications related to memory function, perceptogenesis and `bottom-up' processing in ketamine model psychosis and schizophrenia are discussed.