Defective inhibition of dream event memory formation: a hypothesized mechanism in the onset and progression of symptoms of schizophrenia.

An average person normally spends at least 90 min to 2 h per night dreaming. Nevertheless, memories of dream events are not retrieved while awake unless the person awoke shortly after a dream. It is hypothesized here that schizophrenic delusions initially arise because a system that normally inhibits the formation of memories of dream events is defective. Therefore, memories of dream events or fragments would be occasionally made and placed in the normal memory store. The only reason that we really know anything happened to us in the past is that we have a memory of it, and having a memory of an event is sufficient to really believe it. Therefore, the schizophrenic would believe that the dream events actually happened. It is proposed that this is the basis of primary delusions. Because memories are represented by strengthened neural connections there will be an accumulation of connections that do not correspond to reality. This accumulation may account for other symptoms of schizophrenia such as thought disorder, loosening of associations, and hallucinations. The brain trying to draw conclusions from several memories may be the basis of secondary delusions. Evidence is presented for the ideas that primary delusions are due to memories of dream events, that a substance, with vasotocin-like bioactivity, is released in the brain during dreaming and inhibits memory formation, that the lateral habenula is a brain area involved in vasotocin actions and is affected by neuroleptics, and that brain mechanisms involved in vasotocin actions show pathological alterations in schizophrenia.