Longitudinal Exploration of Cortical Brain Activity in Cognitive Fog: An EEG Study in Patients with and without Anosmia, 2024, Gangemi et al.

[SNT Gatchaman]

Longitudinal Exploration of Cortical Brain Activity in Cognitive Fog: An EEG Study in Patients with and without Anosmia
Antonio Gangemi; Rossella Suriano; Rosa Angela Fabio

BACKGROUND
Long-Covid, characterized by persistent symptoms following acute Covid-19 infection, represents a complex challenge for the scientific community. Among the most common and debilitating manifestations, cognitive fog is a neurological disorder characterized by mental confusion and cognitive difficulties. In this study, we investigated the long-term effects of previous Covid-19 infection on cortical brain activity in patients experiencing cognitive fog symptoms in the medium and long term.

METHODS
A total of 40 subjects (20 females and 20 males) aged between 45 and 70 years (mean age (M) = 59.78, standard deviation (SD) = 12.93) participated in this study. This sample included individuals with symptoms of cognitive fog, both with and without anosmia, and a control group comprised of healthy subjects. All electroencephalography (EEG) data were collected in two sessions, 1 month and 8 months after recovery from Covid-19, to measure the neurophysiological parameters of P300 and beta band rhythms.

RESULTS
The results revealed significant differences in the neurophysiological parameters of P300 and beta band rhythms in subjects affected by cognitive fog, and these alterations persist even 8 months after recovery from Covid-19. Interestingly, no significant differences were observed between the participants with anosmia and without anosmia associated with cognitive fog.

CONCLUSIONS
These findings provide a significant contribution to understanding the long-term effects of Covid-19 on the brain and have important implications for future interventions aimed at managing and treating brain fog symptoms. The longitudinal assessment of cortical brain activity helps highlight the persistent impact of the virus on the neurological health of Long-Covid patients.

Link | PDF (Journal of Integrative Neuroscience) [Open Access]

 

[SNT Gatchaman]

Further changes were observed in the rhythms of alpha, beta, and theta brain waves in the cognitive fog group compared to the control group, suggesting an association with cognitive symptoms. Alpha waves are generally associated with a state of relaxation and a decrease in brain activity in the absence of external stimuli. Variations in alpha waves could indicate impairment in the ability to relax or concentrate, both of which are fundamental for cognitive functions. In our results, we observed a significant decrease in alpha waves in some patients with cognitive fog. This could suggest difficulty in achieving a relaxed mental state or a decrease in attention, both of which influence cognitive performance.

Moreover, beta rhythms, known for their association with sensory information integration and motor activity execution, were reduced in the cognitive fog group compared to the control group. This reduction could indicate impairment in the brain’s ability to effectively integrate environmental information and translate it into appropriate motor actions. This result suggests that individuals with cognitive fog may have difficulty processing sensory information and coordinating motor activities efficiently, with possible impacts on various cognitive domains such as attention, memory, concentration, and decision-making skills.

The key findings of this research have revealed three important discoveries regarding cognitive fog symptoms due to Long-Covid: (a) a significant connection has been found between cognitive fog symptoms occurring after Long-Covid and neurophysiological alterations, particularly in the brain waves of P300 and beta frequency bands; (b) the identified neurophysiological alterations appear to persist in the long term, suggesting that the effects of Long-Covid on brain function may endure over time; (c) the presence or absence of anosmia does not seem to be significantly correlated with the observed neurophysiological alterations. This suggests that anosmia may not be a determining factor in the neurophysiological consequences of Long-Covid.

 

[SNT Gatchaman]

It is important to acknowledge that the manifestation of cognitive fog may vary depending on different conditions and variables involved, which could influence its relationship with neurophysiological parameters depending on the underlying cause. Furthermore, confounding factors such as depression and chronic fatigue syndrome could independently influence brain function, emphasizing the need for more in-depth investigations into the complex interaction among these variables.

Not sure it's confounding factors when it's probably the same thing (eg decreased beta waves).

Cortical hypoactivation during resting EEG suggests central nervous system pathology in patients with chronic fatigue syndrome (2018, Biological Psychology)

A systematic review of quantitative EEG findings in Fibromyalgia, Chronic Fatigue Syndrome and Long COVID (2024, Clinical Neurophysiology)

 

[Hutan]

For beta rhythms:

It is hard to understand exactly what they are measuring:

Moreover, beta rhythms, known for their association with sensory information integration and motor activity execution, were reduced in the cognitive fog group compared to the control group.

As shown in Fig. 5, the group with cognitive fog had significantly lower levels of beta band rhythms than healthy controls

Moreover, beta rhythms, known for their association with sensory information integration and motor activity execution [55], were reduced in the cognitive fog group compared to the control group. This reduction could indicate impairment in the brain’s ability to effectively integrate environmental information and translate it into appropriate motor actions. This result suggests that individuals with cognitive fog may have difficulty processing sensory information and coordinating motor activities efficiently, with possible impacts on various cognitive domains such as attention, memory, concentration, and decision-making

They seem to be talking about the power of the signal

the total absolute power of the signal and the absolute power within each frequency band were calculated for each electrode. In this study, the beta band (14–29 Hz) was considered.

I'm not at all sure that a low powered beta rhythm is a bad thing.


See for example this study on beta rhythms in language:
“Too Many betas do not Spoil the Broth”: The Role of Beta Brain Oscillations in Language Processing
(I found it a good paper to get some understanding of what is being talked about in the Gangemi paper.)

The majority of studies on the relation between beta power and language processing report decrease of power; and only few report increases of power with respect to task manipulation.

For example, during a letter fluency task, where participants read a letter and had to generate as many words as possible, strong left hemispheric decrease of overall MEG (magnetoencephalography) power specifically for the 5- to 15- and 15- to 25-Hz range was shown (Singh et al., 2002). This decrease significantly correlated with the location of BOLD increases in an fMRI-experiment, which was interpreted in terms of increased neuronal activation during this task. Fisher et al. (2008) reported that beta activity in the MEG was a very robust marker for assessing language lateralization in healthy controls and a clinical patient during a verb generation task. The generation of verbs elicited decreases in beta power (15–25 Hz) in the left inferior frontal lobe. The beta decrease typically started at 250–500 ms after auditory noun presentation and sustained throughout the active phase of the task. However, the authors also reported on beta band increases (12–20 Hz) in the right frontal and superior-parietal lobes. Since this task relies on motor activation the beta decrease could be correlated with the typical motor-related beta desynchronization, whereas the beta increase could be related to neuronal synchronization over non-activated motor regions (Pfurtscheller and Lopes da Silva, 2011).

van Elk et al. (2010) have also found a beta (20–30 Hz) decrease in the premotor cortex whilst participants processed action verbs without having an explicit motor task.

While it is possible that the people with cognitive dysfunction were having to work harder than the controls to process stimuli, I think it's also possible that the people with cognitive dysfunction were trying harder than the controls because they cared about the outcome. As far as I can tell (which is not very far), a decrease in the power of beta rhythms during a demanding task is what would be expected.

 

[Hutan]

for P300 latency and amplitude:

As shown in Fig. 1, the group with cognitive fog had significantly higher P300 latencies than healthy controls (main effect of groups. ...These data indicate that both groups are stable in the 8-month assessment compared to the 1-month assessment, meaning that clinical group maintains slowness and control group maintains normal P300 latency.

That's interesting.