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\title{Concomitant physiologic changes as potential confounds for BOLD-based
fMRI: a checklist}



\author[1]{practiCal fMRI}%
\affil[1]{Twitter: @practicalfmri}%


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  \date{May 08, 2026}


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\begin{abstract}
A recent conversation on Twitter led to the suggestion that someone
compile a list of physiological effects of concern for BOLD. That is, a
list of potentially confounding physiological changes that could arise
sympathetically in an fMRI experiment, such as altered heart rate due to
the stress of a task, or that could exist as a systematic difference
between groups. What follows is the result of a PubMed literature search
(mostly just the abstracts) where I have tried to identify either recent
review articles or original research that can be used as starting points
for learning more about candidate effects. Hopefully you can then
determine whether a particular factor might be of concern for your
experiment. ~ This is definitely not a comprehensive list of all
literature pertaining to all potential physiological confounds in fMRI,
and I apologize if your very important contribution didn't make it into
the post. Also, please note that I am not a physiologist so if I go
seriously off piste in interpreting the literature, please forgive me
and then correct my course. I would like to hear from you (comments
below, or via Twitter) if I have omitted critical references or effects
from the list, or if I have misinterpreted something. As far as possible
I've tried to restrict the review to work in humans unless there was
nothing appropriate, in which case I've included some animal studies if
I think they are directly relevant. ~ A final caution before we begin.
It occurs to me that some people will take this list as (further) proof
that all fMRI experiments are hopelessly flawed and will use it as
ammunition. At the other extreme there will be people who see this list
as baseless scare mongering. How you use the list is entirely up to you,
but my intent is to provide cautious fMRI scientists with a mechanism to
(re)consider potential physiologic confounds in their experiments, and
perhaps stimulate the collection of parallel data that might add power
to those experiments. ~ (This article first appeared as a blog post on
practicalfmri.blogspot.com.)%
\end{abstract}%



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