Delay of cognitive gamma responses in Alzheimer's disease

Abstract

Event-related oscillations (EROs) reflect cognitive brain dynamics, while sensory-evoked oscillations (SEOs) reflect sensory activities. Previous reports from our lab have shown that those with Alzheimer's disease (AD) or mild cognitive impairment (MCI) have decreased activity and/or coherence in delta, theta, alpha and beta cognitive responses. In the current study, we investigated gamma responses in visual SEO and ERO in 15 patients with AD and in 15 age-, gender- and education-matched healthy controls. The following parameters were analyzed over the parietal-occipital regions in both groups: (i) latency of the maximum gamma response over a 0–800 ms time window; (ii) the maximum peak-to-peak amplitudes for each participant's averaged SEO and ERO gamma responses in 3 frequency ranges (25–30, 30–35, 40–48 Hz); and (iii) the maximum peak-to-peak amplitudes for each participant's averaged SEO and ERO gamma responses over a 0–800 ms time block containing four divided time windows (0–200, 200–400, 400–600, and 600–800 ms). There were main group effects in terms of both latency and peak-to-peak amplitudes of gamma ERO. However, peak-to-peak gamma ERO amplitude differences became noticeable only when the time block was divided into four time windows. SEO amplitudes in the 25–30 Hz frequency range of the 0–200 ms time window over the left hemisphere were greater in the healthy controls than in those with AD. Gamma target ERO latency was delayed up to 138 ms in AD patients when compared to healthy controls. This finding may be an effect of lagged neural signaling in cognitive circuits, which is reflected by the delayed gamma responses in those with AD. Based on the results of this study, we propose that gamma responses should be examined in a more detailed fashion using multiple frequency and time windows.

Impact of Altered Cholinergic Tones on the Neurovascular Coupling Response to Whisker Stimulation

“…Previous studies on the loss of ACh input on cortical CBF are sparse and reported hypoperfusion after long-term ACh denervation (Waite et al, 1999). Our data further suggest that ACh denervation or loss of integrity of the ACh system, as seen in AD patients (Tong and Hamel, 1999;Mesulam, 2013) and AD mouse models (Aucoin et al, 2005), may contribute to the impaired sensory-evoked oscillations (Başar et al, 2016) and whiskerevoked CBF responses (Niwa et al, 2002; Nicolakakis et al, Figure 5. Correlations between electrophysiological (LFP) and hemodynamic (CBF) signals as a function of frequency band and ACh tone.…”

Emergence of early alterations in network oscillations and functional connectivity in a tau seeding mouse model of Alzheimer’s disease pathology

“…AD-related changes of oscillations may have some similarity to EEG changes during normal aging, as the amplitude of evoked gamma activity is decreased in aged healthy individuals 66 , and were correlated with lower clinical memory measures and behavioral performance in cognitive tasks 67 . A significant reduction or loss of 40 Hz gamma band synchronization in the thalamocortical areas has been described in AD patients 16 , 68 , in aging mice 69 as well as in Aβ mouse model of AD 70 . In the present study, K18-P301L seed mice had consistent reduction in the gamma oscillations 40–80 Hz in response to both standard and deviant stimuli, whereas stronger oscillations coordinate successfully encoded working memory information on standard and deviant trials in buffer treated mice.…”

Increased long distance event-related gamma band connectivity in Alzheimer's disease

“…However, these results mostly come from spontaneous EEG studies as reviewed by Herrmann and Demiralp (2005). More recent studies presented increased gamma responses in AD patients (Stam et al, 2006, Osipova et al, 2006, van Deursen et al, 2008, van Deursen et al, 2011, Başar et al, 2016a). In the present study, we report increased gamma coherence in AD after both sensory and cognitive stimulation.…”