Non-pathological associations - sleep and dreams, deprivation and bereavement

This chapter provides an overview of epidemiological studies on the recurrence of hallucinatory phenomena in the general population and addresses the role of visual hallucinations found in sleep and during states of transition to/from wakefulness. It describes the visual hallucinations during sensory deprivation and bereavement is discussed. The chapter discusses the long-standing debate over the continuity or discontinuity between hallucinations and normal functioning. The prevalence of visual hallucinations after bereavement is higher in pathological conditions as when abnormal grief reactions, post-traumatic stress disorder (PTSD), Charles Bonnet syndrome or reactive psychoses are also present. However, the phenomenon is also described in physiological grief reactions and is generally thought to be largely underestimated. According to the Bayesian model of brain function, information is processed by structurally or functionally embodying a prediction and responding to errors, from the level of single neuronal cells to complex circuits.