How Do Event‐Related Gamma Oscillations Differ in Alzheimer’s Disease From Other Types of Dementia ?

AbstractBackgroundAlthough recent studies showed that gamma frequency entrainment might have therapeutic effects on Alzheimer’s Disease (AD) (Iaccarino et al. 2016), the gamma band abnormalities in AD patients are still poorly understood, while some studies presented increased gamma responses in AD, others showed reduced gamma responses (Güntekin et al., 2022). The differentiation of gamma responses between different dementia types is also not known. The present study aims to analyze the event‐related gamma responses in AD patients and to find out how the event‐related gamma responses differentiate between AD, Parkinson’s disease dementia (PDD), and Lewy Body dementia (DLB).MethodEEG of 17 DLB, 19 PDD, 20 AD patients, and 20 healthy controls was recorded with a 32‐channel EEG device. Subjects had performed visual oddball paradigm during EEG recordings. Event‐related phase locking and Event‐related power were analyzed in three gamma frequency bands (25‐30 Hz, 30‐35 Hz, 35‐48 Hz) in three different time windows (0 200 ms, 200 400 ms, 400‐600 ms) for target and non‐target stimuli. Repeated measures of ANOVA were used with the between‐subjects and within‐subjects factors.ResultTarget responses elicited higher gamma phase locking than the non‐target responses (p<0.05). Healthy subjects had higher gamma phase locking than AD, PDD, and DLB patients (p<0.05). The healthy control group had increased gamma power in the 0‐200 ms time window at frontal and central locations (p<0.05); however, patient groups did not have this early time window increase of gamma responses. Furthermore, although it was non‐significant, gamma phase locking values of PDD and DLB patients were worse than AD.ConclusionThe present study showed that AD, PDD, and DLB patients had reduced event‐related gamma phase locking and power in the early time window compared to healthy elderly controls. The gamma phase locking values of PDD and DLB patients were worse than those of AD patients. The present study showed that similar to AD patients and other dementia types could also have deficits in the gamma frequency band. Since the PDD and DLB patients had even more abnormal gamma band activities, the gamma entrainment could also have positive effects in these groups of patients.