Affiliations : Associate Professor (maître de conférences) at Scalab, Université de Lille, France

Journal reference:

Summary: Could hallucinations be tied to intrusive memories? In individuals with psychosis, this link does seem to exist and further research needs to be done in order to understand how they feed into each other.

Hallucinations are perceptions (or experiences) that appear to be real but occur in the absence of corresponding external stimuli. They are the most common symptom of schizophrenia with 70% of patients reporting having experienced hallucinations. However, 4% of the general population also report experiencing hallucinations, as well as individuals with other pathologies such as Alzheimer’s. Many theories exist to explain the psychological mechanisms behind such experiences. Generally speaking, it is accepted that the starting point is the production of a mental event (a thought or a memory, for example) that is not recognized by the brain as internal and therefore is externalized, i.e. attributed to an external source. This lack of recognition is common in patients with schizophrenia and ultimately is traced back to alterations in self-monitoring processes. 

People with schizophrenia often describe their hallucinations as being associated with a sense of intimacy and containing details of their personal life. Some people also report recognizing the voice(s) they hear. These descriptions, combined with clinical observations, suggest that the hallucinations are related to past events, particularly traumatic events.

By integrating these previous observations, we hypothesized that involuntary personal memories could play a key role in the onset of hallucinations in schizophrenia. Involuntary personal memories are flashbacks of lived events that spontaneously come to mind, generally in response to triggers present in the environment or in thoughts, in the manner of Proust’s famous madeleine. These involuntary memories are therefore based on associative and automatic processes, which make them difficult to control, especially for people with cognitive disorders such as schizophrenia. To investigate whether this link exists, we conducted two studies in the general population, the first cohort had 300 participants and the second cohort had 200. The aim of these studies was to assess whether hallucination-proneness was related to involuntary personal memories characteristics. Our team used standardized questionnaires to assess 1) participants’ propensity for hallucinations, 2) characteristics of their involuntary personal memories, and 3) various factors described in the literature as related to hallucinations (rumination, intrusive thoughts, depressive symptoms, dissociative symptoms, executive disorders, mental imagery, and personality traits).

The results of the two studies provided evidence for a robust relationship between the propensity to experience hallucinations and the frequency of involuntary memories. After controlling for confounding factors (cited above), second to dissociative symptoms, involuntary personal memories were the other most important factor predicting the occurrence of hallucinations in the general population. More precisely, the frequency and emotional intensity of the involuntary personal memories were the characteristics most strongly associated with hallucinations.

These studies highlight the need for further research into the relationship between hallucinations and involuntary personal memories. This will help us better understand hallucination in psychiatric disorders such as schizophrenia, as well as in other illnesses with this symptom and in the general population.

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