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In this chapter, we review the results of neurocognitive and behavioural studies in patients with OCD and schizophrenia and use these data to attempt to identify the key neuropsychological mechanisms. We explore the extent to which associated neuro-behavioural changes may characterise schizo–OCD either as a distinct and clinically relevant schizophrenia subgroup, a more severe form of schizophrenia or a true comorbidity that integrates the psychopathology of both its parent disorders. We conclude that, compared to schizophrenia, schizo–OCD may be associated with additional executive deficits (neurocognitive double jeopardy) featuring impaired performance on specific executive tasks, notably tasks measuring attentional set-shifting and cognitive flexibility and likely to involve fronto-striatal neurocircuitry known to be linked to OCD. However, whilst patients with schizo–OCD and OCD share most OC ritualistic attributes, they also demonstrate behavioural differences, which imply a separate phenotype for the compulsions of schizo–OCD. These differences represent an easily evaluable clinical sign that could contribute toward an improved nosological classification of a range of OC spectrum disorders.

Background Previous studies have revealed that the response of prey species to predatory risk comprised either freezing (when the prey remained immobile), or fleeing (when it ran frantically in order to remove itself from the vicinity of the predator). Other studies, however, have suggested that the prey will adjust its behavior to risk level. The present study was designed to follow the attacks of a barn owl (Tyto alba) on common spiny mice (Acomys cahirinus) and social voles (Microtus socialis guntherei), in order to reveal the correspondence between the behavior of the owl, the risk level at each phase of the owl's attack, and the defensive behavior of the rodents. Results Spiny mice dramatically increased the traveled distance upon the appearance of the owl, and kept moving during its attack while taking long trajectories of locomotion. Defensive response in voles dichotomized: in some voles traveled distance dropped when the owl appeared, reaching zero during its attack. In other voles, traveled distance dramatically increased once the owl appeared and further increased under its attack. These defensive responses developed by gradual tuning of normal locomotor behavior in accordance with the level of risk. Conclusions The phenotypic difference in defensive behavior between voles and spiny mice probably stems from their different habitats and motor capacities. Agility and running capacity, together with a relatively sheltered natural habitat, make fleeing the most appropriate response for spiny mice during owl attack. Clumsiness and relatively limited motor capacities, together with an open natural habitat, account for the dichotomy to freezing or fleeing in voles. Thus, the apparent species-specific anti-predator response in spiny mice and voles is based on species-specific normal locomotor behavior, which depends on the species-specific ecology and motor capacity, and behaviors like defensive attack or escape jump that are specific to life threat. The latter behaviors are brief, and irregularly inlaid in the ongoing locomotor behavior. Finally, our results show that in both voles and spiny mice there is a gradual transition from normal to defensive behavior in accordance with the increase in risk level.