Impaired Cerebral Vascular And Metabolic Responses To Parametric N-Back Tasks In Subjective Cognitive Decline

Previous studies reported abnormally increased and/or decreased blood oxygen level-dependent (BOLD) activations during functional tasks in subjective cognitive decline (SCD). The neurophysiological basis underlying these functional aberrations remains debated. This study aims to investigate vascular and metabolic responses and their dependence on cognitive processing loads during functional tasks in SCD. Twenty-one SCD and 18 control subjects performed parametric N-back working-memory tasks during MRI scans. Task-evoked percentage changes (denoted as delta) in cerebral blood volume (delta CBV), cerebral blood flow (delta CBF), BOLD signal (delta BOLD) and cerebral metabolic rate of oxygen (delta CMRO2) were evaluated. In the frontal lobe, trends of decreased delta CBV, delta CBF and delta CMRO2 and increased delta BOLD were observed in SCD compared with control subjects under lower loads, and these trends increased to significant differences under the 3-back load. delta CBF was significantly correlated with delta CMRO2 in controls, but not in SCD subjects. As N-back loads increased, the differences between SCD and control subjects in delta CBF and delta CMRO2 tended to enlarge. In the parietal lobe, no significant between-group difference was observed. Our findings suggested that impaired vascular and metabolic responses to functional tasks occurred in the frontal lobe of SCD, which contributed to unusual BOLD hyperactivation and was modulated by cognitive processing loads.