Behavioral and electrophysiological evidence of residual cognitive impairment in post-covid brain fog: a visual P300 study.

While known primarily for respiratory symptoms, COVID-19 has also been linked to cognitive impairments, or "brain fog", which affects attention, memory, and processing speed. Brain-fog related cognitive deficits are well-documented in hospitalized patients but less understood in non-hospitalized individuals. Brain fog may reflect dysfunction in cortical structures supporting higher-level cognition, including hippocampal, frontotemporal, and cingulate areas. These regions contribute to the P3b response, an electrophysiological measure of attention and memory used to assess cognitive deficits across neurological conditions, though sparingly in COVID-19. This study examined P3b mean amplitudes in individuals with and without COVID-19-related brain fog and pre-pandemic controls using a visual n-back paradigm. It was hypothesized that the brain fog group would show reduced amplitudes under higher cognitive loads. Results revealed reduced target-related P3b mean amplitudes in the brain fog group relative to both comparison groups, with no group differences for non-targets. This reduction was most apparent over parietal recording sites but did not significantly vary by scalp region. The brain fog group demonstrated lower accuracy and slower reaction times relative to controls. These differences persisted an average of 22.58 months following symptom resolution, suggesting brain fog may be associated with attentional resource deficits that extend beyond subjective recovery.