To study the serial-position effect in a hippocampal disease as early stages of Alzheimer's disease.

Observational study with 168 subjects. Classified according to cognitive performance into mild amnestic cognitive impairment (aMCI) and cognitively normal (NC) and classified by their Alzheimer biomarkers profile (NCBk- = 31, NCBk + = 21, aMCIBk-=45 and aMCIBk + = 71). All subjects were studied with MRI, and voxel-based morphometry was performed to evaluate hippocampal volume. The Rey Auditory Verbal Learning Test (RAVLT) performance and serial position effect on learning and delayed memory were registered.

aMCI showed  deficit in total learning and delayed recall compared with controls; the was no difference between biomarker profiles. In the first trial, the PE between CNBk- was significantly higher (p=0.03) compared with aMCIBk- and aMCIBk+. In total delayed recall there were non-significant differences between aMCI groups, but  RE of delayed recall, showed a significantly better performance of aMCIBk- against aMCIBk+(p=0.028).

RE in Trial6 and delayed recall correlated with T-tau levels (r2= -0.39, p= 0.01 and r2= -0.26 p= 0.027, respectively). Levels of Ab42, hippocampal volume and cortical thickness of the parahippocampal regions did not correlate with any of the effects.

These results show that serial-position effect in the delayed recall is a measure superior to the conventional test scores for the detection of positive biomarkers in aMCI. This effect correlates with the increase in Tau-T in CSF but not with hippocampal volume. This finding suggests serial position effect could be a biomarker of neurodegeneration earlier than MRI.