Increased frontal phase-locking of event-related theta oscillations in Alzheimer patients treated with cholinesterase inhibitors

Abstract

This is a pilot study describing event-related oscillations in patients with Alzheimer-type dementia (AD). Theta responses of 22 mild probable AD subjects according to NINCDS-ADRDA criteria (11 non-treated, 11 treated by cholinesterase inhibitors), and 20 healthy elderly controls were analyzed by using the conventional visual oddball paradigm. We aimed to compare theta responses of the three groups in a range between 4–7 Hz at the frontal electrodes. At F 3 location, theta responses of healthy subjects were phase locked to stimulation and theta oscillatory responses of non-treated Alzheimer patients showed weaker phase-locking, i.e. average of Z-transformed means of correlation coefficients between single trials was closer to zero. In treated AD patients, phase-locking following target stimulation was two times higher in comparison to the responses of non-treated patients. The results indicate that the phase-locking of theta oscillations at F 3 in the treated patients is as strong as the control subjects. The F 4 theta responses were not statistically significant between the groups. Our findings imply that the theta responses at F 3 location are highly unstable in comparison to F 4 in non-treated mild AD patients and cholinergic agents may modulate event-related theta oscillatory activities in the frontal regions.