EEG power bifurcation in the transition zone beta to gamma — from motor function to cognition — in Alzheimer and long COVID patients versus healthy controls revealed by quantitative EEG time series analysis of lateral EEG data

Background Similar EEG abnormalities suggest a nexus from Long COVID (LC) to Alzheimer‘s (AD) and probably to Parkinson‘s disease (PD). Symptoms like memory loss hint to a common cause. Ranasinghe (2020) showed EEG alpha slowing and hyper‐ and hyposynchrony for AD. In LC generalized EEG slowing (Antony, 2020) was reported. There is evidence that switching between brain hemispheres is necessary for scenery and object processing (Brincat, 2021), being disturbed in AD (Maass, 2020). However, explicitly lateral EEG for AD is rarely investigated. We calculate frontal asymmetry index (FAI) for F4/F3 EEG electrodes, which is normally used at alpha frequency for assessing emotional states in major depression (Davidson, 1998), not only for alpha but for further frequencies of AD patients. This possibly yields new biomarkers for AD and LC. Method FAI := logarithm of quotient between F4/F3 power, calculated for frequencies up to 120Hz of AD data taken from (Valladolid, Abasolo, 2017) and (Naples, Babiloni, 2018). AD and healthy control (HC) resting state EEG data from Valladolid were semi‐automatically artifact‐corrected and subdivided into 5s‐epochs. For AD patients and HCs the average of all 5s‐epochs was used for FAI. We recently determined power spectra and FAI from full‐length 10min resting‐state EEG for an LC patient, suffering from tremor. EEG power was calculated by averaged 5s‐epochs of raw‐data for F4/F3 for frequencies up to 100Hz. Result In Fig. 1 (Valladolid) FAI for F4/F3 is shown. A definite bifurcation occurs at 30Hz distinguishing AD group from HC. The power spectrum of an LC patient shows also at 30Hz frequency (Fig. 2) a significant increase, revealing high Beta EEG power conforming with severity of PD‐symptoms (O’Keeffe, 2020). Changing sign of asymmetry (i.e. FAI ∼ 0.3) can be observed at 30Hz (Fig. 3). Conclusion The application of FAI in the full frequency range shall further be investigated as a new biomarker for AD and LC. The EEG frequency range from 25Hz to 35Hz appears to be an important transition zone from motor function to cognition. Abnormalities in this frequency range might be linked to AD, PD and LC and could open a new diagnostic window.