Neural markers of reduced arousal and consciousness in Mild Cognitive Impairment

Abstract

ABSTRACTObjectivesPeople with Alzheimer’s Disease (AD) experience changes in their level and content of consciousness, but there is little research on biomarkers of consciousness in pre-clinical AD and MCI. This study investigated whether levels of consciousness are decreased in people with MCI.MethodsA multi-site MEG dataset, BIOFIND, comprising 83 people with MCI and 83 age matched controls, was analysed. Arousal (and drowsiness) was assessed by computing the theta-alpha ratio (TAR). The Lempel-Ziv algorithm (LZ) was used to quantify the information content of brain activity, with higher LZ values indicating greater complexity and potentially a higher level of consciousness.ResultsLZ was lower in the MCI group vs controls, indicating a reduced level of consciousness in MCI. TAR was higher in the MCI group vs controls, indicating a reduced level of arousal (i.e. increased drowsiness) in MCI. LZ was also found to be correlated with MMSE scores, suggesting a direct link between cognitive impairment and level of consciousness in people with MCI.ConclusionsA decline in consciousness and arousal can be seen in MCI. As cognitive impairment worsens, measured by MMSE scores, levels of consciousness and arousal decrease. These findings highlight how monitoring consciousness using biomarkers could help understand and manage impairments found at the preclinical stages of AD. Further research is needed to explore markers of consciousness between people who progress from MCI to dementia and those who do not, and in people with moderate and severe AD, to promote person-centred care.