Category Archives: neuroimaging

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)

Update on Indian BEOS case: Accused released on bail

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We wrote in December about the murder trial in India that relied heavily on Brain Electrical Oscillations Signature (BEOS) test to prove that Aditi Sharma had “experiential knowledge” of the poisoning of her former fiance, Udit Bharati.  Aditi and her husband, Pravin Khandelwal, were sentenced to life in prison. The original opinion, which we believe contains many serious flaws, is available at the original post.

We recently learned, courtesy of some research by Rajat Rana (thanks to Vinita Kailasanath!), that Aditi and Pravin have been granted bail by the Bombay High Court (documents: Aditi’s bail order and Pravin’s bail order).  Pravin’s sentence was suspended on the grounds that there was no real evidence to tie him to the case as a conspirator. Aditi was released based on the fact that the evidence of her possessing the arsenic-laced prasad was not compelling, and indeed “the possibility of plantation cannot not be ruled out” (sic). The BEOS evidence is not mentioned in either brief.

Watch this space for further news and a complete analysis.

- 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