Despite the high prevalence of Alzheimer's disease (AD), its underlying mechanisms remain poorly understood. An emerging body of evidence supports disorientation as an early marker for AD-related neurodegeneration. In this study we intend to collect, coregister and analyze Positron Emission Tomography (PET) and , functional and structural magnetic resonance imaging (MRI, fMRI) data from AD-spectrum patients to establish orientation as core disturbance in AD.

As population aging is progressively contributing to the global burden of dementia, Alzheimer's disease (AD) is gaining recognition as a health-and social-care priority. Evidence converging from recently published works as well as our own preliminary results, propose that orientation is a sensitive marker for preclinical AD-related neurodegeneration.

Our behavioral results show a simple orientation test to surpass currently used neuropsychological tests in classification of patients along the AD spectrum. A subsequential fMRI study revealed the orientation task to preferentially recruit brain regions identified as susceptible to early AD-related cortical atrophy, including the posterior cingulate cortex, parietooccipital sulcus and hippocampus bilaterally, as well as to significantly overlap with the default mode network (DMN) - a set of interconnected brain regions which were independently recognized as highly perturbed in AD.

In an attempt to further support the role of orientation in AD we propose to use co-registration of several modalities of neuroimaging in patients with AD, mild cognitive impairment (MCI) and healthy controls (HC): resting-state fMRI, task-fMRI, structural MRI and co-registered PET.

1. Resting-state functional magnetic resonance (fMRI) imaging detecting temporally synchronous, spatially distributed, spontaneous low frequency blood-oxygen level-dependent signal fluctuations in task-free settings, that are further clustered into maps of functional large-scale neural networks. A major network revealed in rest is the default DMN. DMN includes the posterior cingulate (PCC), inferior parietal (IPL), lateral (LTC) and medial temporal (MTL), and medial prefrontal cortical regions (MPFC), and is known to be involved in self-referential processes including introspection, memory retrieval, daydreaming and orientation.
2. Task fMRI - using this module we recently demonstrated that fMRI activation generated by orientation task in the person, space and time domains activated the PCC, IPL, and MPFC and MTL hubs of the DMN. This task is now to be applied in patients with AD.
3. Structural MRI - a decrease in hippocampus volume is an early imaging finding followed by cortical atrophy as AD progresses.
4. PET - FDG-PET (glucose metabolism) is known to show temporo-parietal hypometabolism in AD.

Considered these findings alongside ongoing research at the dynamics of anatomical and functional AD associated brain dysfunction, we propose a thorough, and to the best of our knowledge, a never before attempted study aimed at linking markers for AD pathology (cortical atrophy, decrease of functional connectivity, cerebral glucose metabolism) to the disruption of specific cognitive faculties, particularly orientation in the space, time and person domains.

Inclusion Criteria:

1. subjects aged 50-79 years.
2. patients suffering from memory disorder.
3. Test score mini-mental state examinations higher than 20.

Exclusion Criteria:

1. Contraindication to MR imaging
2. pregnant women.
3. patients with contraindications for injection of gadolinium.

The study Population includes patients diagnosed as amnestic mild cognitively impaired, patients suffering from Alzheimer's disease, and age-matched healthy controls.

Only in the case where publication of coded data is required\encouraged by the Journal for publication