Dynamics of brain rhythmic and evoked potentials

Başar, Erol; Gönder, A.; Özesmi, Çiğdem; Ungan, Pekcan

doi:10.1007/bf00342635

Cited by 70 publications

(6 citation statements)

References 18 publications

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“…Although the history of gamma activity began in the 1940s (Adrian, 1942), it was discovered in later years by Freeman (1975) and Başar et al, 1975a, Başar et al, 1975b, Başar et al, 1975c that gamma oscillatory activity reflects a wide variety of cognitive functions. In 1973, the terminology “gamma response” was introduced by Başar and Ungan (1973) to describe hippocampal gamma band activity elicited by stimuli in cats.…”

Section: Introductionmentioning

confidence: 99%

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

Başar

Femir

Emek‐Savaş

et al. 2017

NeuroImage: Clinical

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BackgroundBrain oscillatory responses can be used for non-invasive analyses of cortico-cortical connectivity, local neuronal synchronization, and coherence of oscillations in many neuropsychiatric conditions including Alzheimer's disease (AD). In the present paper, we examine sensory-evoked and event-related gamma coherences elicited by visual stimuli in three sub-gamma bands in two sub-groups of patients with AD (i.e., acetylcholinesterase-inhibitor treated and untreated) and healthy controls.MethodsWe studied a total of 39 patients with probable mild AD (according to NINCDS-ADRDA criteria) who had been sub-divided into untreated (n = 21) and treated (n = 18) (patients either on cholinergic monotherapy or combined therapy with memantine) AD groups, and 21 age-, gender-, and education-matched healthy elderly controls. A simple flash visual paradigm was applied for the acquisition of sensory-evoked coherences. Event-related coherences were elicited using a classical visual oddball paradigm. Both sensory-evoked and event-related gamma coherences were calculated for long-distance intrahemispheric pairs for three frequency ranges: 25–30 Hz, 30–35 Hz, and 40–48 Hz in post-stimulus 0–800 ms duration. The long-distance intrahemispheric pairs from both sides were fronto-parietal, fronto-temporal, fronto-temporoparietal, fronto-occipital, centro-occipital and parieto-occipital.ResultsThe sensory-evoked or event-related gamma coherences revealed that both treated and untreated AD patients had significantly increased values compared to healthy controls in all three sub-gamma bands. Moreover, the treated AD patients demonstrated significantly higher fronto-parietal gamma coherences during both sensory stimulation and oddball paradigm and lower occipito-parietal coherences during oddball paradigm in comparison to untreated AD patients.ConclusionThe present study demonstrated that an increase of gamma coherences was present in response to both visual sensory and cognitive stimulation in AD patients in all gamma sub-bands. Therefore, gamma oscillatory activity seems to be fundamental in brain functions at both the sensory and cognitive levels. The increase of gamma coherence values was not due to cholinergic treatment to any significant extent, as both treated and untreated AD patients had increased gamma coherence values compared to healthy controls. The use of coherence values reflecting brain connectivity holds potential for neuroimaging of AD and understanding brain dynamics related to the effects of medication.

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Section: Introductionmentioning

confidence: 99%

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

Başar

Femir

Emek‐Savaş

et al. 2017

NeuroImage: Clinical

View full text Add to dashboard Cite

show abstract

“…The history of gamma activity began in the 1940s ( Adrian, 1942 ). In subsequent years, Freeman (1975) and Başar et al, 1975a , Başar et al, 1975b , Başar et al, 1975c indicated that gamma oscillatory responses reflect a wide variety of functions. In 1972, Başar and Özesmi introduced the terminology “gamma response” to describe hippocampal gamma band activity elicited by external stimuli in cats.…”

Section: Introductionmentioning

confidence: 99%

Delay of cognitive gamma responses in Alzheimer's disease

Başar

Emek‐Savaş

Güntekin

et al. 2016

NeuroImage: Clinical

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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.

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“…For example, early studies have reported an influence of alpha power and/or phase on the perception, evoked response and reaction times (e.g. [10–14] ). Only in recent years, neuroscientific research has re-gained increasing awareness that alpha oscillations substantially influence perception, behavior and neuronal processing.…”

Section: Introductionmentioning

confidence: 99%