Comparison of auditory P300 responses in healthy elderly, people with mild cognitive impairment and people with Alzheimer's disease

Abstract

Background: The role of beta responses in cognitive load was least understood in comparison to other frequency bands. The aim of the present study is to investigate the role of beta response oscillations upon cognitive load in healthy subjects and in subjects with mild cognitive impairment (MCI). Methods: Seventeen consecutive patients with MCI (mean age 70,76 65,62years) according to Petersen’s criteria and Seventeen ageand education-matched normal elderly controls (mean age 68,49 65,48 years) were included in the study. Visual oddball paradigm was used in the experiments. Oscillatory responses were recorded from F 3, F z, F 4, C 3, C z, C 4, TP 7, TP 8, P 3, P z, P 4, O 1, O z and O 2 scalp electrodes. EEG-evoked power, inter-trial phase synchronization and event related beta responses filtered in 15-20 Hz were obtained in response to target and non-target stimuli for both groups of subjects. Results: EEG-evoked beta power, inter-trial phase synchronization of beta responses and event related filtered beta responses were significantly higher in response target stimulation in comparison to non-target stimulation in healthy subjects (p<0,05). On the other hand, there were no evoked beta power differences between target and non target stimuli in MCI patients. Furthermore, upon presentation of visual oddball paradigm occipital electrodes enhanced higher beta response in comparison to other electrode sites (p< 0,0001). Conclusions: The results of the present study clearly indicated that target stimulation elicited higher event related beta power, event related beta phase locking and event related filtered beta responses than non-target stimulation in all electrode sites in healthy subjects. Event related beta increase could be related to attention and cognitive activity. The increased beta response upon presentation of target stimuli in healthy subjects implies that beta oscillations could shift the system to an attention state and had important function in cognitive activity. This may, in future, open the way to consider the beta activity as universal operator in the brain in cognitive processes.