Normal Aging: Alterations in Scalp EEG Using Broadband and Band-Resolved Topographic Maps

Abstract

Given the majority of age-related diseases have been described as disconnection syndromes, understanding the functional connections of normal aging is of considerable importance. Here, an EEG-based scalp level analysis has been performed to identify the alterations in the synchronized brain regions in aged, compared to young persons. Two groups, aged and young subjects were studied, each consisting of 18 participants. First, conventionally extracted broadband topographic maps, also called microstate maps, were examined. The results showed an overall dominant alteration: a uniform decrease in synchronization of brain regions related to cognitive processing resources that was observed only when the maps C and D were characterized in temporal parameters. However, no remarkable change in the spatial distribution was found between the groups. This failure in identifying differences in the spatial distribution was hypothesized to be due to the presence of superimposed signals of several frequencies in the broadband signal that is used for the extraction of microstate maps. Second, spectrally resolved band-wise topographic maps, which we have shown, in a previous study, are able to detect spectral details associated with broadband microstates maps, were used to address this failure. The use of the instantaneous frequency concept is essential in the extraction of band-wise topographic maps, and represents a novelty compared to current studies. The method consists of three steps: (a) from EEG signal, the Empirical Mode Decomposition method is used to extract underlying oscillatory components; (b) these intrinsic oscillatory components are then amplitude demodulated and subjected to numerical equations for the calculation of instantaneous features, such as amplitude, and frequency; finally, (c) based on these instantaneous features, band-wise topographic maps are extracted. Here, as a first application to aging data, these band-wise topographic maps have shown the capability of capturing the age-related changes in both spatial distributions, and in temporal characterization. Spatially, the potential distribution in the aged and the young subject groups, respectively, showed differences, while, in temporal characterization, both increases and decreases were observed, suggesting the lengths of synchronized activities vary differentially, and in accordance with results from fMRI studies. These observed differences also support the dedifferentiation and compensation mechanisms.

Characterization of the Functional Dynamics in the Neonatal Brain during REM and NREM Sleep States by means of Microstate Analysis

“…Indeed, spatial fluctuations and temporal modulations of alpha power have been linked to the emergence and persistence of specific microstates (Milz et al 2017 ; Croce et al 2020 ). Nevertheless, recent studies raised the question about whether the broad-band activity should be spectrally differentiated in order to identify and describe spatio-temporally overlapping spectral patterns (Javed et al 2019 , 2020 ). A recent study in adults found that during NREM sleep low frequencies dominated in all microstates, whereas the EEG power for high frequencies was higher during wakefulness (Brechet et al 2020 ).…”

Age-related changes of whole-brain dynamics in spontaneous neuronal coactivations

“…An EEG study reported increased beta oscillations indicating greater GABAergic inhibitory activity within motor cortices of older than younger adults 19 . On the contrary, whole-brain age-related changes have mainly been reported in resting-state neuroimaging studies 8 , 13 , 17 , 18 , 20 – 22 . A resting-state fMRI study reported weakened within-network functional connectivity (FC), reduced system segregation, and lowered local efficiency in all primary sensory and cognitive networks 13 .…”

“…Resting-state MEG studies have shown age-related spectral power decreases in low frequencies (e.g., delta) over most sensors covering the whole head 8 , 23 . Spectrally-resolved resting-state EEG topographic maps have revealed microstates from the delta to gamma bands showing significant age-related global differences in their spatial maps 20 . In these investigations, band-specific EEG/MEG power data 8 , 17 and fMRI amplitude data 10 , 17 were commonly used to evaluate regional changes (i.e., intra-region measures), while FC measures computed from either neurophysiological 16 or hemodynamic signals 13 , 24 , 25 evaluating dependence, interaction, and integration between regions are mainly used for cross-region and whole-brain changes (i.e., inter-region measures).…”

“…Based on the measure of whole-brain phase synchronizations in BOLD signals 21 , the older adults exhibit reduced ability to access a so-called rich-club brain state (therefore lowered occurrence) 31 . In EEG, age-related changes have also been reported in the transient brain states known as microstates 20 , 32 , where a microstate related to cognitive processes is less visited and with reduced lifetimes. Initial evidence has further indicated that measures of brain dynamics have better sensitivity on age-related effects than measures of spatial patterns 20 , as well as in revealing disease-related changes 33 .…”

“…The present study examined age-related changes in whole-brain dynamics in healthy individuals between 6 to 65 years old by studying multiple cortical co-activation patterns (CAPs). The analysis of CAPs characterizes whole-brain dynamics with a set of transient brain states at the single-timeframe resolution 34 , 35 , which advances the definition of brain states from scalp-based field EEG measurements, e.g., microstates 20 , to electrical currents on anatomic structures of direct neuronal relevance. The high temporal resolution of EEG and the nature of framewise analysis in obtaining CAPs provided the capability to study much faster dynamics (i.e., up to 100 Hz) at the whole-brain scale than fMRI (< 0.1 Hz).…”