Functional Connectivity within Temporal Brain Regions and Conversion to Alzheimer’s Disease in Amnestic Mild Cognitive Impairment

Background: structural and neurochemical abnormalities in temporal lobe and temporoparietal junction (T-TPJ) are seen not only in Alzheimer’s disease (AD) but also in amnestic mild cognitive impairment (aMCI). At the same time, studies of conversion to dementia focused on functional characteristics of these regions are lacking. The aim was to search for patterns of functional connectivity (FC) within T-TPJ that differentiate patients with aMCI with future conversion to AD from stable aMCI patients and healthy controls. Patients, Comparison Group and Methods: patients with aMCI who further converted to dementia due to AD (converters, n = 15), patients with stable aMCI ( n = 12), and healthy individuals without cognitive deficits ( n = 29) underwent resting-state functional magnetic resonance imaging. FC between cortical T-TPJ structures was compared between groups separately for each hemisphere (one-way ANCOVA and post hoc between-group comparisons). Results: an increased FC between posterior parts of left middle and inferior temporal gyri was observed in converters compared to other groups. There was an inverse correlation between this FC and delayed recall of words (MoCA scale) in the entire sample, however, this correlation did not reach the level of statistical significance ( p = 0.055). Conclusions: the posterior parts of left middle and inferior temporal gyri are involved in auditory verbal memory and storing of visual images associated with a word, respectively. Therefore, а pattern of increased FC observed in future converters to AD may be a consequence of pathological processes that have already started and/or compensatory mechanisms.