Category Archives: fMRI

What a dead salmon reminds us about fMRI analysis

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This has been making the rounds in the neuroscience world, but deserves attention in cross-disciplinary fields.  A group of top-notch fMRI researchers presented an unusual paper at June’s Human Brain Mapping conference.

Paper titleNeural correlates of interspecies perspective taking in the post-mortem Atlantic Salmon: An argument for multiple comparisons correction

Blog headline: fMRI Gets Slap in the Face with a Dead Fish

Salmons have very small brains.

Salmons have very small brains.

In short, researchers scanned a dead fish while it was “shown a series of photographs depicting human individuals in social situations. The salmon was asked to determine what emotion the individual in the photo must have been experiencing.”

Clearly, the fish did not perform well at the task, and thus we have not learned much about interspecies perspective taking.  The work is, however, a compelling and humorous demonstration of the problem of multiple comparisons.  This is a principle in statistics that basically says when you’re looking at enough bits of information (i.e. doing lots of statistical tests), some will seem to be what you’re looking for – purely by chance.  In fMRI experiments, there are a LOT of pieces of data to compare, and without statistical correction for this phenomenon (which is not always done), some will indeed be significant, just by chance.

Lead author Craig Bennett explains further on his blog:

In early 2008 I was working with my co-adviser George Wolford on a presentation he was giving regarding the multiple comparisons problem in fMRI. We were discussing false positives in MRI phantom data and I brought up the idea of processing the salmon fMRI data to look for some ‘active’ voxels. I ran the fish data through my SPM processing pipelines and couldn’t believe what I saw. Sure, there were some false positives. Just about any volume with 65,000 voxels is going to have some false positives with uncorrected statistics. Rather, it was where the false positives occurred that really floored me. A cluster of three significant voxels were arranged together right along the midline of the salmon’s brain.

Remember that the fish was dead.  There was surely no BOLD signal changes going on in a dead fish’s brain.  This is likely not a physiological artifact; it is a statistical one.  Furthermore, the voxels were clustered together – something that may be expected to happen in an “actual” activation and thus used as a threshold for analysis.  Also, it was just one fish!  (No apparent speculation in the paper about what may have happened if this were a school of fish compared to appropriate control school of fish.)

Bennett et al are apparently having a hard time getting the paper published.  The use of multiple comparisons corrections in fMRI studies is a contentious one, as some researchers think it may be overly conservative and thus miss true positives.  As a solution, Bennett suggests reporting both sets of data, corrected and uncorrected.

The moral of the story for interdisciplinary folks: note whether multiple comparisons correction data have been reported (or not).  And always bear in mind that there are a lot of assumptions and decisions being made behind the ultimately reported data in any neuroimaging study.

– Emily Murphy (h/t Alexis Madrigal @ Wired)


No Lie MRI being offered as evidence in court

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It has come to our attention that No Lie MRI has produced a report that is presently being offered as evidence in a court in Southern California.  A hearing about the admissibility of this evidence is imminent.

The case is a child protection hearing being conducted in the juvenile court.  In brief, and because the details of the case are sealed and of a sensitive nature, the issue is whether a minor has suffered sexual abuse at the hands of a custodial parent and should remain removed from the home.  The parent has contracted No Lie MRI and apparently undergone a brain scan.  The No Lie MRI-produced report reads in part as follows:


The defense plans to claim the fMRI-based lie detection (or “truth verification”) technology is accurate and generally accepted within the relevant scientific community in part by narrowly defining the relevant community as only those who research and develop fMRI-based lie detection.  [Note: California follows its own version of the Frye test of admissibility, not the current federal test under Daubert.]

Limiting the “relevant community” to only those who research and develop fMRI based lie detection is without merit, if only because such a definition precludes effective or sufficient peer-review.  Indeed, it is arguable such a narrowly-defined community has a strong incentive to exaggerate its claims of accuracy and overlook unanswered questions for financial gain if such techniques are “legally admissible.”

The few practitioners who research and develop fMRI-based deception detection are not the only qualified people to comment on the accuracy and validity of the technique.  Statisticians familiar with Bayesian analysis, cognitive neuroscientists familiar with technical and analytical constraints, and researchers working to elucidate the neural basis of memory, decision-making, and social behavior should all make up the “relevant scientific community” for such a complex and as-yet poorly characterized technology.   Further, I suspect the community of peer-reviewers that have reviewed the articles being proffered in support of the evidence of fMRI testing on deception is probably a useful proxy for the legally relevant scientific community, and extends well beyond the handful of researchers working directly on fMRI-based deception detection.

I will post again soon with more details and criticisms about the claims in the statement produced by No Lie MRI – mainly, that their external validation task was inconclusive in the individual, yet the testing proceeded with the case-related probe questions and found to be determinative that the parent was not lying about denying sexual abuse of the child.  Further, that the repetition of three critical questions (as above) four times each seems incredibly unlikely to produce sufficient power to detect a robust neural response that could be accurately classified as deceptive/non-deceptive.

Please add your own views and suggestions, and check back for updates.

Emily Murphy

PETA calls for Brain Scan of Michael Vick: how neuroscience is once again being called upon to solve what are fundamentally normative problems

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Michael Vick used to be the NFL’s highest-paid player.  That was before he was caught bankrolling a gambling ring that killed dogs by shot-gun, electrocution, drowning, and heinous beating  (hard words even to write).  He was charged with conspiracy and is currently serving his 23 month sentence.  Despite this incredibly public, negative exposure, there are still some NFL teams who are interested in Vick after his sentence is complete in July.  Will it be the Dallas Cowboys?  Will he be able to regain his instincts as a passer, given how the NFL has become so much of a passing league?   I can’t pretend to understand how commentators could focus on these mundane questions, given what we know about Vick’s life off of the field. But before I wax too moralistic…I don’t think you have to be a dog-lover like me to see the shame and atrocity in the way the pit-bulls were treated in Vick’s “Bad Newz Kennels.”  It’s hard to imagine a human being capable of that kind of violence toward something so innocent and defenseless.  But Vick wasn’t charged with being a bad person, he was charged with conspiracy.  And that sentence is almost up.

The Commissioner of the NFL, Roger Goodell, stated that he owed it to the public to make sure Vick was capable of remorse before he ever wore an NFL jersey again.  Oh, that’s helpful.   I can’t imagine that a statement of remorse will go far enough to restore his public image, but perhaps it would allow the bottom-line-blinded teams to take him back into the fold.

While I don’t think that a public statement of remorse should morally cut it, I also do not support the inquisition by People for the Ethical Treatment of Animals (PETA).  Officials from PETA sent a letter to the NFL commissioner today saying that Vick should be checked to see if he is a psychopath or sociopath before he can return to the NFL.  And the method that they specifically suggested?  Brain scans.  PETA wants Vick to undergo a full psychiatric evaluation and a brain scan to determine whether he has anti-social personality disorder or psychopathy.  Excuse me, what?

Functional brain imaging cannot be used to diagnose psychiatric illnesses.  Full stop.  Not yet.  Researchers such as Kent Kiehl are currently making strides in locating neurological  markers of psychopathy, but they are not yet able to reliably use brain scans to diagnose someone with ASPD or psychopathy.  (Kiehl posits that psychopathy or APSD may be caused by a defect in the “paralimbic system,” but he acknowledges this is still a theory).   Because of the methodological limitations of fMRI, even if there were a deficit, the scanner might not pick it up.  Further, there could be reduced metabolism in the brain regions of interest, and yet this may not have any connection to psychopathy or ASPD.  So at this point, the scans would add nothing to explain Vick’s behavior.

Assuming for a second that brain scans could actually diagnose these disorders, why would this information be relevant at all in determining whether or not Vick should return to the NFL?  Would such diagnoses exculpate him from his bad acts, or make it impossible for him to return to the NFL, as he might strike again and sully the brand?  According to the letter from PETA to Goodell, PETA wants to use the brain scans to answer the question, “whether Michael can change.”  While parole boards and sentencing judges may ask whether someone “can change” (i.e., will they offend again)  PETA is not a legal entity and it cannot impose that sort of process on the NFL.  As the law has nothing to say in this case (where the sentence will have run and the NFL teams can hire or fire whomever they want) it seems to me that this is really a normative question for society to decide.  And one way we make social decisions is to trade signals back and forth —  in petitions, outrage, public apologies, and appeals for psychiatric tests.

But what is the relevance of this finding if it were somehow possible to show he would re-offend?  That it’s ok to brutally kill animals once, but not twice?  I guess it is hard for me to understand how PETA’s argument works; asking whether or not Vick can change seems to me to be the wrong question.  If Vick truly has no volitional control (as evidenced by the dazzling, commissioned brain scan…?) and he could not change his behavior, then might that make us a bit more sympathetic to his predetermined actions? The sword can cut either way.

Vick did what he did.  A signal of apology may or may not move anyone to think he should be restored to his previous NFL glory.  But the question that actually lies underneath all of this is to what degree society ought to punish someone who did what Vick did.  The law has not answered that.  Neuroscience cannot answer that.  Only we can answer that, by using a low-tech device of consumer activism: the boycott.

— Teneille Brown