Keeping track of reality: why some people are better than others at remembering what really happened
5 October 2011
Scientists at the University of Cambridge's Behavioural and Clinical Neuroscience Institute found that normal variation in a fold at the front of the brain called the paracingulate sulcus (PCS) might explain why some people are better than others at accurately remembering details of previous events - such as whether they or another person said something, or whether the event was imagined or actually occurred. The research is published today in the 'Journal of Neuroscience'.
This brain variation, which is present in roughly half of the normal population, is one of the last structural folds to develop before birth and for this reason varies greatly in size between individuals in the healthy population. The researchers discovered that adults whose magnetic resonance imaging (MRI) scans indicated an absence of the PCS were significantly less accurate at memory tasks than people with a prominent PCS on at least one side of the brain. Interestingly, all participants believed that they had a good memory despite one group's memories being clearly less reliable.
Dr Jon Simons from the Behavioural and Clinical Neuroscience Institute and the Department of Experimental Psychology at Cambridge, who led the research, said: "As all those who took part were healthy adult volunteers with typical educational backgrounds and no reported history of cognitive difficulties, the memory differences we observed were quite striking. It is exciting to think that these individual differences in ability might have a basis in a simple brain-folding variation.
"Additionally, this finding might tell us something about schizophrenia, in which hallucinations are often reported whereby, for example, someone hears a voice when nobody's there. Difficulty distinguishing real from imagined information might be an explanation for such hallucinations. For example, the person might imagine the voice but misattribute it as being real."
PCS reductions have been reported in previous studies of schizophrenia, and Dr Simons argues that the results of this new study are consistent with the idea that this structural variability might directly influence the functional capacity of surrounding brain areas and the cognitive abilities that they support.
For the study, the researchers recruited 53 healthy volunteers based on their brain scans, which showed either a clear presence or absence of the PCS in the left or right brain hemisphere. Participants were presented either with well-known word-pairs like "Laurel and Hardy" or with the first word of a word-pair and a question mark ("Laurel and ?"). In the latter condition, participants were instructed to imagine the second word of the pair. Then, either they or the experimenter was instructed to read the whole pair out aloud. After a delay, a memory test was given where participants tried to remember whether they had seen or imagined the second word of each previously encountered pair, or whether they or the experimenter had read the pair out aloud. Participants with absence of the PCS in both brain hemispheres scored significantly worse than the others at remembering both kinds of detail.
The Behavioural and Clinical Neuroscience Institute at the University of Cambridge is funded by a joint award from the Medical Research Council and the Wellcome Trust.
Image: Folds in the brain. Credit: Heidi Cartwright/Wellcome Images
Reference
Simons JS et al. A specific brain structural basis for individual differences in reality monitoring. J Neurosci 5 October 2011.
