Cerebral responses to famous face recognition as a potential functional biomarker of mild cognitive impairment.

Background: Social cognition impairments-including difficulties in recognizing personally familiar faces-occur early in mild cognitive impairment (MCI) and can lead to social withdrawal, reduced motivation, and secondary depression. Face recognition is central to social cognition, yet its neural basis in MCI remains insufficiently understood. This study examined whether task-based fMRI during famous face recognition could capture early alterations in the parahippocampal gyrus (PHG) and posterior cingulate cortex (PCC), key nodes supporting semantic access and internally directed cognition within the default mode network (DMN). Methods: Thirty-two participants (20 healthy controls, 12 MCI) completed two fMRI tasks: famous vs. non-famous face judgment and face vs. object categorization. A 2 × 2 factorial analysis assessed Group and Task effects, and small-volume correction was applied to PHG and PCC. Results: Behavioral accuracy was comparable between groups; however, whole-brain analyses revealed markedly reduced activation in the left PHG and PCC in the MCI group during socially meaningful face processing. ROI analyses further demonstrated that the left PHG reduction remained significant after FWE correction, whereas PCC showed a weaker reduction that did not survive correction for multiple comparisons. Conclusion: These findings suggest early alterations in PHG-PCC networks that precede observable behavioral decline in MCI. In particular, reduced activation in the left PHG may reflect early disruptions in semantic access and internally directed processing. Assessing these socially relevant neural circuits alongside established amyloid and tau biomarkers may provide complementary functional insight into early cognitive vulnerability in individuals at risk for dementia.