Real-space path integration is impaired in Alzheimer’s disease and mild cognitive impairment

• Path integration (PI) depends on structures affected early in Alzheimer’s disease (AD).
• We examined PI in patients with mild AD and amnestic mild cognitive impairment (aMCI) and assessed the role of the hippocampus, entorhinal and inferior parietal cortices in this association.
• We used a novel real space Arena Path Integration Task.
• AD and aMCI subjects were impaired in PI accuracy.
• Hippocampal volume and thicknesses of entorhinal and parietal cortices partially explained differences in PI between controls, aMCI and AD subjects.

IntroductionPath integration (PI) is an important component of spatial navigation that integrates self-motion cues to allow the subject to return to a starting point. PI depends on the structures affected early in the course of Alzheimer’s disease (AD) such as the medial temporal lobe and the parietal cortex.ObjectivesTo assess whether PI is impaired in patients with mild AD and amnestic mild cognitive impairment (aMCI) and to investigate the role of the hippocampus, entorhinal and inferior parietal cortex in this association.Methods27 patients with aMCI, 14 with mild AD and 18 controls completed eight trials of Arena Path Integration Task. The task required subjects with a mask covering their eyes to follow an enclosed triangle pathway through two previously seen places: start–place1–place2–start. Brains were scanned at 1.5T MRI and respective volumes and thicknesses were derived using FreeSurfer algorithm.ResultsControlling for age, education, gender and Mini-Mental State Examination score the aMCI and AD subjects were impaired in PI accuracy on the pathway endpoint (p = 0.042 and p = 0.013) compared to controls. Hippocampal volume and thickness of entorhinal and parietal cortices explained separately 36–45% of the differences in PI accuracy between controls and aMCI and 28–31% of the differences between controls and AD subjects.ConclusionsPI is affected in aMCI and AD, possibly as a function of neurodegeneration in the medial temporal lobe structures and the parietal cortex. PI assessment (as a part of spatial navigation testing) may be useful for identification of patients with incipient AD.