July 22, 2025, 11:21 am | Read time: 4 minutes
Among the most frequently mentioned long-term effects of a COVID-19 infection are persistent fatigue and exhaustion. Additionally, recovered patients report memory problems. A new study suggests that the ability to distinguish between similar memories is particularly affected. Researchers have examined this potential long-term COVID effect and the underlying neurocognitive mechanisms in more detail.
Study Examines Specific Long-Term Cognitive Deficits After COVID
Even though not as many people are contracting the coronavirus as during the pandemic, the risk remains. And infections long overcome can still affect individuals permanently, in the form of long-term effects. These longer-term health effects, commonly referred to as Long COVID, are often associated with changes in the brain and specifically the nervous system, as FITBOOK explains in more detail here.1 However, the exact mechanisms behind the observed cognitive and affective changes have not yet been thoroughly researched—a gap the new study aimed to address.2
Details of the Study
For an online screening survey, researchers initially collected data from over 1,400 individuals. Among the participants were both people with and without previous COVID-19 infections, and among them, those with and without persistent symptoms. From this large group, a smaller sample was later selected for in-depth laboratory analyses: a group of COVID-19 survivors with long-term symptoms and a healthy control group. Participants ranged in age from 18 to 90 years.
The study participants underwent digital neuropsychological tests specifically designed to examine memory functions. One of the central tests involved remembering previously heard word pairs and later recalling them correctly. This is a classic test for what is known as episodic memory. Another test assessed how well participants could resist distracting stimuli while learning. Additional control tasks were used, focusing on maintaining attention over extended periods and filtering out distractions.
Difficulty Distinguishing Memories as a Long-Term COVID Effect
The analysis revealed that memory problems were particularly evident when participants were distracted while learning—a problem significantly more pronounced in the Long COVID group. Participants with Long COVID performed significantly worse on the word pair task under distraction than the control group. This suggests that the difficulties cannot be solely explained by disruptions in the hippocampus—the brain area responsible for storing information. Rather, the ability for cognitive control, or the targeted management of attention, also seems to be impaired. Researchers suspect a disrupted interaction between the prefrontal cortex (attention) and the hippocampus (memory formation).
Furthermore, it was found that many former patients had trouble distinguishing between similar memories. This was evident in tests where participants had to report on previously seen visual stimuli, such as slightly different objects or scenes, which they were later asked to identify as exactly the same, only similar, or new. This phenomenon is known as mnemonic discrimination ability. Notably, this potential long-term COVID effect occurred independently of age, education, or psychological factors like stress or depression. Other cognitive functions, such as flexible thinking or general memory, remained largely intact.
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Significance of the Study
“Our results clearly demonstrate for the first time in a large sample a specific memory disorder following a COVID-19 infection that cannot be explained solely by psychological stress or general physical exhaustion,” explains study leader Prof. Dr. Patric Meyer, professor at Heidelberg SRH University, in a university statement.3 Many of the observed memory problems are therefore not due to mere forgetfulness but to a disruption in the interaction between attention and memory formation. Affected individuals may have difficulty filtering out irrelevant stimuli while learning, resulting in similar memories becoming blurred and harder to distinguish.
The study results thus provide important clues for developing targeted rehabilitation strategies. Possible approaches could include training programs that specifically strengthen the ability to control attention. At the same time, some questions remain unanswered.
Limitations
For example, it is not clear how long ago the participants’ COVID-19 infections occurred. This aspect could be relevant for assessing this potential long-term COVID effect of being unable to distinguish memories. Additionally, only individuals with mild to moderate illness courses were included in the laboratory analysis. Whether the results can be applied to severe cases remains uncertain. Moreover, imaging techniques such as MRI were not used. Instead of specific neural changes, only behavioral data were evaluated. Since there was no preliminary survey, it cannot be said with certainty whether the observed deficits are indeed a consequence of the infection or existed beforehand. Finally, the in-depth analysis is based on a relatively small sample, which further limits its significance.