Investigating the narrator hypothesis: a systematic review on somatoparaphrenia

Somatoparaphrenia is a disorder of body ownership whereby the left side of the body is disowned and attributed to someone else after right hemisphere damage. Defective multisensory integration is an underlying mechanism of this disorder. Therefore, the narrator hypothesis posits that impaired multisensory integration in the right hemisphere leads to the transmission of distorted information regarding the contralateral side of the body. Upon receiving this information, the left hemispheric narrator reasons that the affected limbs are not part of the body representation and consequently not a source of concern, resulting in the confabulations. This systematic review aims to investigate the narrator hypothesis. Since somatoparaphrenia is assessed through interviews, the objective of this thesis is to analyze the emotion in somatoparaphrenic patients’ speech to examine whether the narrator’s demotion of the limb is reflected in the linguistic component of the disorder. We consulted online databases like PubMed and Google Scholar, as well as manual citation searching. The papers were screened per the inclusion criteria which entail that the papers must be about somatoparaphrenia, written in English, and contain transcripts of assessment interviews, leading to n=12 papers. The interviews were formatted to include only the patients’ (n=39) responses and uploaded onto Linguistic Inquiry and Word Count Software. A non-parametric paired sample t-test was conducted with the negative and positive emotion scores. The resulting p- value of 0.987 and a small effect size indicate a neutral emotion. This is in line with the narrator hypothesis, depicting that the narrator is unconcerned about the limb following its exclusion from the body’s representation. To support this finding, we provided evidence for the disconnection view by highlighting impaired connectivity that produces defective multisensory integration and ownership and linked it to impaired emotional regulation in somatoparaphrenia. Therefore, this thesis provides a neural basis for the narrator’s nonchalance and allows for a more comprehensive understanding of somatoparaphrenia.