As individuals with Alzheimer’s disease (AD) move from the mild cognitive impairment stage to moderate and severe dementia, complex awareness deteriorates although lower-level sensory awareness is relatively maintained. Most conscious processes also become more impaired as AD progresses, including attention, working memory, episodic memory and executive function, while unconscious processes, such as procedural or muscle memory, operant conditioning (behavior controlled by consequences), and priming (where the experience of stimulus affects the processing of a similar stimulus) are relatively spared. However, as damage spreads across different cortical regions in dementias such as AD, corresponding aspects of conscious awareness becomes diminished and then lost.

One measure of brain complexity, the perturbation complexity index-state transitions (PCI-ST), can be calculated by recording EEG signals following a transcranial magnetic stimulation pulse. This measure has previously been used to determine when people are in coma versus in a minimally conscious state. A new study asks whether this same measure could be used to evaluate the integrity of conscious processing in people with AD. 

According to researchers from Boston University Chobanian & Avedisian School of Medicine, the answer is yes. They found that brain complexity in response to magnetic stimulation was reduced in people with AD compared with people aging normally.