Research on an area of the brain that monitors the difference between external reality and sensations and feelings that arise internally suggests that physical differences may correlate with different sizes of the controlling area. The reality-monitoring area in people who do not experience auditory hallucinations appears to be larger than in people who do. An article comments:
Many mentally well people hear voices (or “auditory verbal hallucinations”) – in fact, around 6-7 per cent of adults in the general population report having had such experiences at some point in their lives.
The researchers scanned all their participants’ brains, specifically looking at the length of a brain structure involved in “reality monitoring” or telling the difference between internally and externally generated experiences.
Garrison and her colleagues wanted to test the idea that a problem with reality monitoring contributes to the voice-hearing experience in patients with schizophrenia, but not in healthy people who hear voices. To test this account, they used the scans to measure the length of a brain structure called the paracingulate sulcus (PCS) – this is the most frontal area of the medial prefrontal cortex and previous research has suggested that it is involved in reality monitoring. For instance, people for whom the PCS is completely absent (up to a quarter of the general population by some estimates) tend to struggle with reality monitoring tasks.
As they predicted, the researchers found that their patient volunteers had a shorter PCS than the healthy non-voice-hearing controls, and a shorter PCS than the voice-hearing healthy controls.[1] In contrast, there was no (statistically significant) difference in the length of the PCS between the voice-hearing healthy controls and the controls who did not have hallucinations.
Garrison’s team believe this result is consistent with there being two routes to auditory hallucinations (see image, below). For healthy people who hear voices, the researchers believe the origin is in hyper-activation of sensory parts of the brain involved in processing auditory information. For patients with schizophrenia, by contrast, they believe there is a sensory component combined with a problem with reality monitoring.
What isn't know is how differences in brain morphology affects people differently in everyday life without regard to hallucination. This line of research is in early early stages. The researchers write in the original paper: “Although our framework is admittedly simple, it might provide a useful basis to assist the understanding of hallucinations across clinical and nonclinical groups, and areas for future focus have been discussed above. The source monitoring framework suggests that decisions are made as to the source of a percept through comparison of its contextual, semantic, perceptual, or cognitive features with characteristic traces relating to internal or external sources.” It is thus not clear how important differences in reality monitoring is for clinically healthy people in various aspects of life.
Footnote:
1. “Also, it’s worth noting that, among the healthy voice-hearers in this study, the length of the PCS was intermediary between the patients and non-voice-hearing controls. It’s possible, the researchers admitted, that the reason the difference in PCS length between the two healthy groups was found to be statistically non-significant may have been due to a lack of statistical power. They said that replication of this study with larger samples could clarify this issue, adding that ‘…further research is [also] needed to to assess the extent to which the present results generalise to other nonclinical populations with hallucinations who may have different etiology and phenomenology of hallucinatory experience.’ ”
B&B orig: 6/24/19
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