OLFACTORY DEFICITS AND FUNCTIONAL CONNECTIVITY DISRUPTIONS IN PATIENTS WITH SUBJECTIVE COGNITIVE DECLINE (SCD)

Abstract

Patients with subjective cognitive decline (SCD) are the high risk group for developing Alzheimer's disease (AD). Olfactory fMRI)was used to investigate olfactory activation and connectivity in SCD and cognitively normal (CN) adults, and to explore early functional markers for AD. Twenty SCD participants and 20 age-, education-level-matched CN elderly were recruited. Full set of neurocognitive tests, olfactory threshold and identification battery tests (Osmic Enterprise, LLC), and olfactory fMRI were administered to each participant. The differences in olfactory behavior scores, neuropsychological scales, and task-fMRI brain activation maps between the two groups were analyzed, and the correlation between brain activation and olfactory behavior scores was evaluated. Brain regions, which had significant different activations were used as seeds for resting-state functional connection analysis. There was no statistically significant difference in olfactory threshold between SCD and CN subjects, but SCD showed a significant decrease in olfactory identification ability (p < 0.05). There was also a significant decrease (p < 0.05) in the SCD self-rating scale, the immediate and delayed test of Philadelphia verbal learning, while the remaining neuropsychological scales were within normal range. In the olfactory fMRI, activation in bilateral primary olfactory cortex was significantly reduced in SCD patients, including bilateral entorhinal cortex, amygdala, piriform cortex, anterior olfactory nucleus, and head of the hippocampus (Fig. 1). The resting-state functional connectivity with the bilateral primary olfactory cortex (POC) showed that the functional connections between the POC and frontal cortex and the default mode network (DMN) were significantly weakened in the SCD patients (Fig. 2 and 3, AlphaSim correction with voxel level p<0.01 and cluster level p<0.05).