Assessing awareness in severe Alzheimer’s disease

Abstract

AbstractBackgroundThere is an urgent need to understand the nature of awareness in severe AD to ensure effective person‐centred care. Transcranial Magnetic Stimulation (TMS) combined with Electroencephalography (EEG), Event Related Potentials (ERPs) and functional Magnetic Resonance Imaging (fMRI) are robust techniques for assessing awareness in clinical populations who are unable to communicate. We present novel feasibility and preliminary data on using these methods to assess capacity for consciousness and contents of awareness in severe AD.Method a) TMS‐EEG was performed in 6 healthy older controls and 3 people with severe AD. The perturbational complexity index (PCIST) was calculated as a measure of capacity for conscious awareness. b) ERPs were recorded during a masked visual perception paradigm and analysed for the presence of visual awareness negativity and P400 components, previously identified as associated with conscious visual perception. c) An fMRI movie‐viewing task, validated in previous studies to demonstrate activation in a fronto‐parietal network during conscious engagement with the film was also conducted.Result a) Participants with severe AD demonstrated a PCIST around the previously identified threshold for consciousness, suggesting reduced capacity for consciousness. b) In response to viewing faces, two patients with severe AD provisionally demonstrated similar visual awareness negativity to healthy controls. c) Healthy controls and one person with severe AD revealed spatially, but not temporally similar activation in a fronto‐parietal network, suggesting differences in conscious engagement with the movie.ConclusionThese biomarkers provide experimental approaches to assess awareness and improve understanding and care for people with severe AD.