The network substrate of confabulatory tendencies in Alzheimer's disease.

Confabulatory phenomena are rare in the early stage of Alzheimer's disease (AD), are often provoked and are triggered by questions or in response to neuropsychological testing. In this retrospective study functional connectivity alterations were investigated for the first time in a group of patients with early AD who had shown evidence of verbal and non-verbal confabulatory tendencies. Resting-state functional magnetic resonance imaging (fMRI) scans of 18 confabulating patients were compared with those of 18 non confabulators. The finding showed that confabulators had decreased connectivity between a seed region in the right inferolateral frontal cortex and right mediotemporal and insular regions, and increased connectivity with frontal areas and a homologous region on the left. The seed control region in the left inferolateral frontal cortex showed increased connectivity with midline frontal and anterior cingulate regions, while a decrease was found in temporal areas. Confabulatory tendencies appear in early AD as a result of disconnection between crucial computational hubs in frontal and mediotemporal regions. This disconnection is coupled with the presence of up-regulation of frontal activity, and especially of midline and anterior cingulate regions, which might disrupt efficient output monitoring in confabulators.