Stimulus-induced Robust Narrow-band Gamma Oscillations in Human EEG Using Cartesian Gratings

2023

Eur J of Neuroscience

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Functional connectivity (FC) indicates the interdependencies between brain signals recorded from spatially distinct locations in different frequency bands, which is modulated by cognitive tasks and is known to change with ageing and cognitive disorders. Recently, the power of narrow‐band gamma oscillations induced by visual gratings have been shown to reduce with both healthy ageing and in subjects with mild cognitive impairment (MCI). However, the impact of ageing/MCI on stimulus‐induced gamma FC has not been well studied. We recorded electroencephalogram (EEG) from a large cohort (N = 229) of elderly subjects (>49 years) while they viewed large cartesian gratings to induce gamma oscillations and studied changes in alpha and gamma FC with healthy ageing (N = 218) and MCI (N = 11). Surprisingly, we found distinct differences across age and MCI groups in power and FC. With healthy ageing, alpha power did not change but FC decreased significantly. MCI reduced gamma but not alpha FC significantly compared with age and gender matched controls, even when power was matched between the two groups. Overall, our results suggest distinct effects of ageing and disease on EEG power and FC, suggesting different mechanisms underlying ageing and cognitive disorders.

Section: Methodsmentioning

confidence: 99%

Healthy ageing and cognitive impairment alter EEG functional connectivity in distinct frequency bands

Kumar

2023

Eur J of Neuroscience

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“…We implemented a fully automated artifact rejection framework (for details, see (Murty et al, 2020(Murty et al, , 2021Murty and Ray, 2022), in which outliers were detected as repeats with deviation from the mean signal in either time or frequency domains by more than 6 standard deviations, and subsequently electrodes with too many (30%) outliers were discarded. Subsequently, stimulus repeats that were deemed bad in more than 10% of the other electrodes (see below) or in the visual electrodes were discarded.…”

Section: Artifact Rejectionmentioning

confidence: 99%

Healthy aging and cognitive impairment alter EEG functional connectivity in distinct frequency bands

Kumar

2023

Preprint

Self Cite

Functional connectivity (FC) indicates the interdependencies between brain signals recorded from spatially distinct locations in different frequency bands, which is modulated by cognitive tasks and is known to change with aging and cognitive disorders. Recently, the power of narrow-band gamma oscillations induced by visual gratings has been shown to reduce with both healthy aging and in subjects with mild cognitive impairment (MCI). However, the impact of aging/MCI on stimulus-induced gamma FC has not been well studied. We recorded electroencephalogram (EEG) from a large cohort (N=229) of elderly subjects (>49 years) while they viewed large cartesian gratings to induce gamma oscillations and studied changes in alpha and gamma FC with healthy aging (N=218) and MCI (N=11). Surprisingly, we found that aging and disease changed power and FC in different ways. With healthy aging, alpha power did not change but FC decreased significantly. MCI reduced gamma but not alpha FC significantly compared with age and gender matched controls, even when power was matched between the two groups. Overall, our results show distinct effects of aging and disease on EEG power and FC, suggesting different mechanisms and the potential to use EEG stimulus-induced FC along with power for early diagnosis of Alzheimer's Disease.

“…For eyes open data, we used the artifact rejection framework as described in (Murty et al, 2020, 2021; Murty and Ray, 2022) and the steps are summarised here. Eye-blinks or change in eye position outside a 5° fixation window during −0.5 s to 0.75 s from stimulus onset were noted as fixation breaks and removed offline.…”

Section: Methodsmentioning

confidence: 99%

Slope of the power spectral density flattens at low frequencies (<150 Hz) with healthy aging but also steepens at higher frequency (>200 Hz) in human electroencephalogram

Aggarwal

2023

Preprint

Brain signals such as electroencephalogram (EEG) often show oscillations at various frequencies, which are represented as distinct ″bumps″ in the power spectral density (PSD) of these signals. In addition, the PSD also shows a distinct reduction in power with increasing frequency, which pertains to aperiodic activity and is often termed as the ″1/f″ component. While a change in periodic activity in brain signals with healthy aging and mental disorders has been reported, recent studies have shown a reduction in the slope of the aperiodic activity with these factors as well. However, these studies only analysed PSD slopes over a limited frequency range (<100 Hz). To test whether the PSD slope is affected over a wider frequency range with aging and mental disorder, we collected EEG data with high sampling rate (2500 Hz) from a large population of elderly subjects (>49 years) who were healthy (N=217) or had mild cognitive impairment (MCI; N=11) or Alzheimer′s Disease (AD; N=5), and analysed the PSD slope till 800 Hz. Consistent with previous studies, the 1/f slope up to ~150 Hz reduced with healthy aging. Surprisingly, we found the opposite at higher frequencies (>200 Hz): the slope increased with age. This result was observed in all electrodes, for both eyes open and eyes closed conditions, and for different reference schemes. Slopes were not significantly different in MCI/AD subjects compared to age and gender matched healthy controls. Overall, our results constrain the biophysical mechanisms that are reflected in the PSD slopes in healthy and pathological aging.