Mechanism of disorientation in Alzheimer's disease

In nondemented amnesics, disorientation mostly reflects a failure to select memories that pertain to ongoing reality (increased temporal context confusion; TCC), a failure strongly associated with orbitofrontal damage. In the present study, we used the same paradigm--2 runs of a continuous recognition task--in 23 patients with mild to moderate Alzheimer's disease (AD) (Clinical Dementia Rating Scale score of 1-2). We found that disorientation was frequent in this sample (52%). However, although it correlated moderately well with general measures of dementia severity, verbal episodic memory and executive functioning, there was no significant correlation with TCC. Thus, disorientation in AD appears to reflect general cognitive decline rather than a specific cognitive failure such as increased TCC. This finding is compatible with the different distribution of degeneration in AD and the orbitofrontal damage typically present in severely disoriented amnesics.