Tuesday, February 1, 2022

You Don't Know What You're Missing

Attention and memory deficits persist for months after recovery from mild Covid
University of Oxford News, Jan 2022

"Although our Covid-19 survivors did not feel any more symptomatic at the time of testing, they showed degraded attention and memory."
-Dr Sijia Zhao of the Department of Experimental Psychology, University of Oxford
Repasted from above article:
All the participants had previously suffered from Covid-19 but were not significantly different from a control group at the time of testing on factors such as fatigue, forgetfulness, sleep patterns or anxiety.

But, they displayed significantly worse episodic memory and a greater decline in the ability to sustain attention over time than uninfected individuals for 6-9 months.

Note, the COVID-19 survivors in this study were young, mean age around 28, n=136.

How bad was it? Here is a measurements for context: Over the course of the 9-minute experiment, control participants’ accuracy dropped from 78.5% to 75.4%, whilst COVID survivors started with a similar baseline at 75.5%, reducing to 67.8% ... For a 30-minute memory test, COVID-19 survivors showed a significant memory decrement which was larger than in controls by 9.2%.

And to be specific: The larger episodic memory decrement amongst COVID-19 survivors was driven by errors in which the wrong orientation was chosen for a correct item. This difference suggests that the deficit in episodic memory in the COVID group might be associated with a deficit in binding information in memory. 

Interesting: word-memory tasks showed no change. 

How it might happen, if you're interested: One investigation of COVID-19 survivors demonstrated that the most severely cognitively affected patients demonstrated a degree of cognitive impairment accompanied by hypometabolism in the frontoparietal regions. These brain regions are implicated in sustained attention as well as in episodic memory. Reassuringly, the follow-up study of Hosp et al. showed slow but evident improvement after 6 months.

Last thing: The good news is that COVID-19 survivors performed well in most cognitive abilities tested, including working memory, executive function, planning and mental rotation. 

via University of Oxford: Rapid vigilance and episodic memory decrements in COVID-19 survivors. Zhao et al. Brain Communications. Jan 2022. https://academic.oup.com/braincomms/article/4/1/fcab295/6511053

How Is This Related to Smell?
We already know that changes in our ability to smell were the primary symptom of the initial varieties of covid. Some of us still deal with these changes. But something we also know, regardless of any pandemic, is that smell is tightly linked to episodic memory -- "grandma's attic" or "first boyfriend's cologne" -- and a subset called autobiographical memory. These type of memories tie together people, places, feelings and smells into the olfactory cluster. Chemosensation enabled the first navigation, as primordial protists sniffed their way through the soup of early Earth. Chemosensation enabled the first social experience, when you detected your mother's immunity profile via her amniotic fluid. And chemosensation enabled your primate ancestors to remember where that really ripe fruit tree was. 

So it does seem appropriate that a virus attacking your olfactory neurons would also affect your episodic memory.

Image credit: Just astrocytes, upsplash

Post Script:
For those who haven't heard about this enough already, here's a good reminder of what Long Covid is: People who survive COVID-19 infection present a significantly higher risk of major neurological and psychiatric conditions, particularly if they were hospitalized. These include acute cerebrovascular events such as ischaemic stroke and intracerebral haemorrhage. In addition to severe neurological conditions, there can also be more chronic, longer-term consequences such as fatigue, low motivation, disturbed mood and poor sleep—all commonly reported symptoms amongst survivors, the so-called long-COVID (see recent review). -source

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