Reading the thoughts of a dead salmon: a poignant tale

How do our brains translate sound waves into information about how far away the sound generator is from our ears?  The direction a sound is coming from is pretty easy to decipher because the sound hits our ears at different times; the difference is minute but enough for our brains to make sense of with respect to where the sound originates.  Distance is another question.  And what about soft-but-nearby vs loud-but-distant?  How does our brain distinguish between these two?

A Scientific American blog, The Scicurious Brain, posted on just this subject the other day, and we're happy it caught our eye.  Scicurious describes a new paper in PNAS by Kopco et al., "Neuronal representations of distance in human auditory cortex."  That is, it's basically an fMRI (functional magnetic resonance imaging) study of where activity happens in the brain when people hear sounds at different distances.

The researchers exposed 12 subjects to sounds of different intensities in a 'virtual reverberant environment', simulating sound coming from 15-100 cm away.  They conclude that neurons in a particular part of the brain (posterior nonprimary auditory cortices, that is a part of the brain already known to be involved in making sense of sound waves) are "sensitive to intensity-independent sound properties relevant for auditory distance perception".  I.e., this part of the brain determines the distance of a sound, at least within 100 centimeters.  How it does so is another question entirely.

fMRI results, Kopco et al.

So, this study doesn't really tell us a whole lot more than we knew before, and Scicurious points out that fMRI studies should be interpreted with caution.  Indeed, she says -- and this is why we love her post -- you can get fMRI signal from a dead fish.  Alas, that finding was reported in 2009 -- so sorry we didn't know about it until now!

Neuroscientist Craig Bennett purchased a whole Atlantic salmon, took it to a lab at Dartmouth, and put it into an fMRI machine used to study the brain. The beautiful fish was to be the lab’s test object as they worked out some new methods.

So, as the fish sat in the scanner, they showed it “a series of photographs depicting human individuals in social situations.” To maintain the rigor of the protocol (and perhaps because it was hilarious), the salmon, just like a human test subject, “was asked to determine what emotion the individual in the photo must have been experiencing."

If that were all that had occurred, the salmon scanning would simply live on in Dartmouth lore as a “crowning achievement in terms of ridiculous objects to scan.” But the fish had a surprise in store. When they got around to analyzing the voxel (think: 3-D or “volumetric” pixel) data, the voxels representing the area where the salmon’s tiny brain sat showed evidence of activity. In the fMRI scan, it looked like the dead salmon was actually thinking about the pictures it had been shown.

“By complete, random chance, we found some voxels that were significant that just happened to be in the fish’s brain,” Bennett said. “And if I were a ridiculous researcher, I’d say, ‘A dead salmon perceiving humans can tell their emotional state.’”

One readily criticizes seances and crystal balls, because we feel that conjuring is a scam rather than a science.  It is not possible to read someone else's thoughts, certainly not if they are among the dearly departed.  Or so we had thought.  Because if dead salmon can think, why not dead Aunt Mazie? 

We are not psychologists or neuroscientists, though we are scientists of a sort and we perhaps have a lot of nerve.  But we don't have enough nerve to challenge the usefulness of fMRI, not after universities have all bought their $1 Million instruments and boasted about how modern they now are.  We feel we should temper our tendency to think that salmon can't really have afterthoughts.  People have, we must admit, often reported 'near-death' experiences, but they weren't actually totally dead at the time!  But a salmon that was cold as a dead fish should not be sending out brain waves.  Of course we are assuming that there wasn't a short in the investigators' fMRI machine. An alternative of course is that there really is an afterlife, and its afterglow appears in the brain for a while--at least thinkers at seminaries should pay close attention to these startling findings.

We cannot personally attest to whether one can communicate with salmon by seance, because it has never crossed our minds to attempt it.  Nor have we any views on whether the cadavers of other fish (or amphibian) species might have similar postmortem brainwaves.  For the same reason, we must cease our glib assertions that "dead men tell no tales," and remain mute about your ability to get in touch with old Aunt Mazie.

Many many fMRI scans have been done since 2009 when the dead salmon results were publicized, so clearly dead fish thinking haven't dimmed researchers' enthusiasm for or faith in the method.  No test is perfect, and every test is at risk of yielding false positives or false negatives, and fMRIs are obviously no exception.   Nor are seances.  There are statistical corrections that can be made to fMRI results -- we don't know of any for seance results -- because fMRI readings have a lot of 'natural noise.'  But added to all the other caveats about fMRI's -- and the fact that whether or not we accept the fMRI findings about where in the brain we process information about how far away a sound is coming from, we still don't know how the brain does it -- we'll retain our skepticism about how much fMRI's can really tell us about ourselves.