Thread by @ZdenekVrozina

Does the brain always return to baseline after COVID?
A new multimodal MRI study suggests the answer may be - not always.
After infection, some brains may remain in a different network state - and we still do not know if that state is temporary, compensatory, or maladaptive🧵

The important part is not one single MRI finding.
The strength of this study is that it combines three MRI layers
structural MRI - grey matter volume,
diffusion MRI - white-matter microstructure,
resting-state fMRI - functional connectivity.

The study included 76 people recovered from COVID-19 and 51 healthy controls.
The authors looked at the whole recovered group, and then stratified COVID participants by severity
non-hospitalized vs hospitalized.
That matters, because some effects only became visible when severity was taken into account.

On structural MRI, there was no major grey-matter difference when all recovered COVID participants were compared with controls.
But in the hospitalized group, the authors found localized grey-matter volume loss in the orbitofrontal cortex and frontal pole.

That location matters.
The orbitofrontal cortex is involved in emotion, motivation, decision-making, reward processing and integration of body signals.

It sits in a circuit that makes biological sense for post-COVID symptoms such as fatigue, mood changes, altered motivation, cognitive slowing and attention problems.

The second layer was diffusion MRI.
Here the signal was broader.
The authors found widespread white-matter microstructural abnormalities across association and commissural tracts - including changes in fractional anisotropy, mean diffusivity and mode of anisotropy.

This is where the story becomes more interesting.
White matter is the wiring.
If grey matter is where much of the processing happens, white matter is how distant regions talk to each other.
So even if there is no obvious lesion, altered white-matter microstructure can still mean altered network communication.

Third layer was resting-state fMRI.
This looks at how brain regions communicate when the person is not performing a task.
The key finding was altered thalamocortical connectivity, especially involving the mediodorsal thalamic nucleus and cortical regions including anterior cingulate, parietal and occipital areas.

The thalamus is not just a sensory relay station.
It helps regulate attention, perception, cognition and the integration of internal and external signals.
So when thalamocortical connectivity changes after COVID, it raises a serious question-
is the brain compensating - or has the system settled into a new, less efficient state?

This is the central point.
These MRI findings do not prove irreversible damage.
But they suggest that after COVID, some people may not simply return to baseline.
Their brain may reorganize.
And we do not yet know whether that reorganization is temporary, protective, incomplete, or maladaptive.

This is why brain fog is such a weak term.
Fog sounds vague.
What similar studies are pointing to is much more concrete.
Fronto-limbic circuits,
white-matter pathways,
thalamocortical connectivity,
network-level reorganization.

That is not fog.
That is altered brain network biology.

The authors themselves frame the study as an attempt to integrate structural, microstructural and functional architecture after COVID - because previous findings were often heterogeneous and limited to one imaging modality.

That is why multimodal MRI matters here.
One layer may look subtle.
Three layers together can show a pattern.

And the pattern is not random.
The affected systems - orbitofrontal cortex, limbic-related pathways, thalamocortical networks - are exactly the systems you would suspect in a condition involving fatigue, attention deficits, sleep disturbance, sensory dysregulation, anxiety or altered motivation.

This is a preprint, not peer reviewed.
It is cross sectional.
The viral variant is not reported.
The exact average time from infection to MRI is not clearly stated.

But it supports a more uncomfortable idea
after COVID, some people may carry measurable changes in the architecture and communication of brain networks.
Not just symptoms.
A different network state.

Maybe some of this is compensation.
Maybe some of it resolves.
Maybe some of it becomes chronic.
That is exactly the problem. We do not yet know.

So the real question is still not simply
Did the person recover?
The better question may be
Recovered to what baseline?
Because after COVID, the body may clear the acute infection - while the nervous system is still negotiating the cost.

Mishra at al., Fronto-limbic and Thalamocortical Network Alterations after COVID-19 Recovery: a Multimodal MRI Study. medrxiv.org/content/10.648…