What does the broken brain say to the neuroscientist? Oscillations and connectivity in schizophrenia, Alzheimer's disease, and bipolar disorder

Abstract

The application of the concept and methods of brain oscillations has been an important research area in neurosciences. In the last decades, besides the application in cognitive processes, the study of changes in brain oscillations in diseases has also become an important focal point of research. In the present paper, some remarkable examples in three different diseases are taken into consideration: 1) schizophrenia (SZ), 2) Alzheimer's disease (AD), 3) bipolar disorders (BD). In the current literature, decreased oscillations in cortical recordings are observed in most of the pathologies. For example, decrease of gamma activity in SZ, decrease of delta activity in almost all diseases, as well as frequency shifts in alpha and the lower frequencies were recorded. However, there are also paradoxical cases in which an increase of oscillatory activities is observed. In BD, whereas alpha activity is greatly decreased, a huge increase of beta activity is observed. Or, in SZ, a paradoxical increase of gamma activity can be observed during cognitive loading. We also observed paradoxical changes in the analysis of connectivity. In AD, we find that alpha, delta, and theta coherences between distant parts of the cortex are greatly decreased, whereas in the gamma band, event-related coherences attain very high values. The comparison of the results and paradoxical changes in diseases may lead to important conclusions related to the web of oscillations and neurotransmitters. In turn, we could gain new insights to approach "brain function", in general.

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

“…Both treated and untreated AD patients had higher coherence values than healthy controls in all three gamma frequency sub-bands (25–30 Hz, 30–35 Hz, 40–48 Hz). In our previous study, we presented our preliminary findings on event-related gamma coherences in twelve untreated AD patients and twelve healthy controls (Başar et al, 2016b). An increase of gamma coherence values in three different frequency ranges was reported during a visual oddball paradigm.…”

“…These include, (1) the different dynamics of resting state EEG and evoked and/or event-related oscillations upon application of a sensory or cognitive task (i.e., oddball paradigm) (Başar, 1980, Başar et al, 2016b); (2) inhibitory interneuron impairment in AD; (3) disrupted Ca 2 + signaling; (4) drug effects (i.e., cholinergic and glutamatergic modulation).…”

Staging model in psychiatry: Review of the evolution of electroencephalography abnormalities in major psychiatric disorders

“…Studies have reported large decrease in alpha activity in drug‐free BD euthymic patients (Basar et al, ; Kano, Nakamura, Matsuoka, Iida, & Nakajima, ; Ozerdem, Guntekin, Tunca, & Basar, ) compared to healthy controls, whereas in schizophrenia, spontaneous alpha activity is only slightly reduced (Basar et al, ). In BP patients with acute hypomania or depression, alpha activity was rather increased (Moeini, Khaleghi, & Mohammadi, ) and the authors concluded that the increased alpha power, which corresponds to a decrease in the thalamic metabolism leading to diminished attention, is consistent with BD presentation.…”

Whole genome sequence association and ancestry‐informed polygenic profile of EEG alpha in a Native American population

“…Alpha enhancement has also been frequently observed during mental imagery, internal attention, and various creativity-related demands such as imagination and ideation [Cooper et al, 2003; Fink and Benedek, 2014]. Changes in alpha activity have also been associated with select mental and behavioral disorders [Başar, 2013; Başar and Güntekin, 2013; Başar et al, 2016; Ducci et al, 2009; Enoch et al, 1999; Herning et al, 1994; Loo and Makeig, 2012; Mazaheri et al, 2014]. …”