Most of us have no problem telling the real from the imagined. Or so we think. Reality monitoring, the incorporation and distinction of internal thoughts and imaginings from external experiences and memories, typically happens seamlessly for most individuals. However, there are times when we cannot recall if someone else told us about that interesting article or whether we read it ourselves, or if we remembered to lock the door before leaving the house or not. Did we actually do or hear these things, or did we only imagine them? This is a common problem in patients with schizophrenia, who at times cannot distinguish between what they think they remember or believe to be true, and what actually occurred.
A new study on reality monitoring published last week in the Journal of Neuroscience reveals that many of us are not as good at making this distinction as we might think. Additionally, the ability to discern between perceived and imagined events may be rooted in one very specific region of the brain, which nearly 30% of the population is missing. Led by Marie Buda and Dr. Jon Simons at the University of Cambridge*, researchers administered a very particular type of memory test to healthy participants who had been pre-selected based on the prominence of the paracingulate sulcus (PCS) in their brains. Running rostral-caudal (front to back) and located in the anteriomedial (middle-frontal) prefrontal cortex, this region is involved in higher level cognitive functioning and is one of the last parts of the brain to mature. Consequently, it can be relatively underdeveloped or even seemingly absent in many people. This is particularly the case in individuals with schizophrenia, where as many as 44% of patients lack this particular region.
Participants for the current study were chosen from a database of individuals who had previously undergone an MRI scan and clearly showed a presence or absence of the PCS in either one or both of the neural hemispheres. The memory task in question involved a list of common word pairs such as "yin and yang" or "bacon and eggs". These words were either presented together (perceive condition), or only one word was presented and the participant was to fill in the complimenting phrase (imagine condition). The second portion of the experiment involved the source of this information, i.e. whether the subject or the experimenter was the one to read off or verbally complete the pair. After the task, the subject was asked to report whether the pair was fully perceived or imagined, and whether this information was attributed to themselves or the experimenter. They were also asked to rate their confidence in both of these responses.
Participants with a complete absence of the PCS in both hemispheres performed significantly worse on the reality monitoring task than individuals who exhibited a definite presence of the sulcus. This difference was based on their source attribution memory (themselves vs. the experimenter); performance on the perceive or imagine condition did not differ between the groups. Interestingly, the two groups also did not differ in their confidence in their responses. Thus, even though the PCS-absent group performed significantly worse on attributing the source of the information, they were still just as confident in their answers as individuals who responded correctly, indicating a lack of interospective awareness in the absent group in regards to their memory abilities.
It should be noted that there was also a correlation between overall gray matter volume in the prefrontal and motor cortices and scores on the reality monitoring task. This is important as it may indicate that there are other regions involved in this process outside of the PCS, and the authors caution that this enhanced ability may stem from an increase in gray matter and connectivity in the medial prefrontal cortex, rather than from the PCS itself.
These findings could have useful applications in clinical psychiatry. As stated above, an impairment in reality monitoring is often associated with schizophrenia, and the absence of the PCS could serve as a potential biomarker for this disorder. Additionally, although not commonly discussed in terms of reality monitoring, another psychiatric diagnosis that could potentially benefit from this type of research is obsessive compulsive disorder (OCD). OCD often consists of obsessions and the urge for frequent compulsive checking of things, such as whether one remembered to turn off the stove. This ruminating and checking behavior could be indicative of a breakdown in reality monitoring where patients can not determine whether a target action actually occurred or not. While this problem is not encompassing of all OCD patients, reality monitoring disability could be a potential area to investigate in those patients for whom checking is a significant problem.
*Disclaimer: Marie Buda and Jon Simons are fellow members of the Department of Experimental Psychology at the University of Cambridge with me.