Route-following deficits in amnestic mild cognitive impairment: Is the dual encoding of route-following strategies impaired?

BackgroundOne of the earliest signs of amnestic mild cognitive impairment (MCI) and neurodegenerative dementia (ND) is spatial disorientation, e.g., getting lost on previously familiar routes. Healthy individuals often follow routes by combining two strategies, serial recall of directions and cue-direction associations, but the integration of these two strategies may be degraded in amnestic MCI and ND.ObjectiveTo evaluate whether impaired integration of the two strategies (dual encoding) contributes to the route-following deficits in amnestic MCI.MethodsTwenty-five patients with amnestic MCI and 25 age-matched healthy controls (HC) followed routes through virtual mazes that allowed the use of the serial order strategy only (maze S), the associative cue strategy only (maze A), or both strategies (maze SA).ResultsFor longer routes, accuracy in maze SA exceeded that in mazes S and A, confirming the existence of a dual encoding benefit. The magnitude of this benefit was comparable in both groups. In contrast, performance on an additional dual-task test was poorer in MCI than in HC.ConclusionsWe attribute the dissociation between preserved dual encoding and impaired dual-tasking in amnestic MCI not to fundamental differences in the underlying mechanisms, but rather to the different ecological validity of the two experimental paradigms. Our findings suggest that spatial orientation training in amnestic MCI need not target dual encoding.