How animals, Shrek, and Yoda stimulate your neurons.

Is CellularDog thinking 'yum'? or 'aww'? (I took this picture)
(and, yes, sometimes I wear ugly Christmas pants)

Recent studies have found that specific cells in the human brain respond to specific things.  And I don't just mean those vision neurons that respond to lines or circles that you learned about in psychology 101.  There are neurons in your brain that selectively respond to concepts (like celebrities, faces, and animals).  Let's talk about animal cells...(that is human cells that respond to pictures of animals.)

Studies recording from cells in the human brain can be conducted on patients who need electrodes implanted for other reasons (such as epilepsy monitoring). Testing neuronal responses in 41 such patients, Mormann et al., (2011) found that certain cells in the right amygdala responded to pictures of animals (They also showed pictures of people and places, but these neurons only responded to the animal pictures). 

Mormann et al., 2011 Supplemental Figure 2a

Here are some of the pictures that they showed the patients.  The blue dashes below each picture represents each time a particular neuron fired.  As you can see this particular neuron fires a lot when a picture of an animal is shown, but is not so excited by buildings or Brad Pitt. 

While there were cells that responded to all animals presented, some cells only responded to certain animals, like this one, which prefers mice and rabbits, and doesn't respond to rhino, tiger or eagle. 

Mormann et al., (2011) supplemental figure 2b

They also tested pictures of two 'ambiguously animalistic' characters: Shrek and Yoda. Many cells in the right amygdala that responded to animals also responded to pictures of Shrek and Yoda, so they classified them as animals...

animal, mineral, or vegetable?

A side note on scientific practice:

Is this correct scientific practice to classify something because it fits in with the rest of your data?

No way, Jose.
They should have done all their statistics without those two 'ambiguous' pictures because their classification was based on the very result they were investigating.
(To be fair, they apparently did test everything whithout shrek and yoda and it "did not alter any of the reported findings")

but, here's another way to look at it:



some pseudo-data

I want to do a study to test whether people like red or blue objects.  So I line up a bunch of red and blue objects on a table and have people come pick out five of their favorite.  I record what fraction of the favorite items is red and what fraction is blue.  But just for fun I throw in some purple objects.  Then I look at all my data and see that there were more favorite objects that were blue than red, and I see that the people who picked a lot of blue objects also picked a lot of purple objects. So I decide to classify the purple objects as 'blue' because the same people who picked blue picked purple.
The finding that blue is preferred over red is not altered, because people preferred blue already (see pseudo-data), but it's better to report the findings without the a posteriori classification of purple as blue. 

So yeah, no. Don't do that.

Ok back to the study, which despite this 'Yoda and Shrek are animals a posteriori' thing, is still pretty awesome. 

The Big Question: What does it mean that these cells respond only to pictures of animals?

In the supplementary discussion, the authors point out that the amygdala neurons fire 300-400 ms after the picture is presented.  They say that this timing is almost certainly after the identification of the picture would have taken place.  That mean that these neurons are probably not the ones telling you 'this is a tiger', or 'this is a spider', but instead might encode a response to knowing that it is a tiger or a spider. 

Are these neurons coding for that "awww" feeling that you get when you look at cute things? The authors say 'probably not' because the spider is not really an 'awww' inducing image. (Though given that yoda and shrek stimulate these neurons, would pictures of babies, stuffed animals, or other abstractions stimulate them as well?)

Are these neurons coding for a fear response? This is the amygdala after all. But again the authors say 'probably not'. 

"Previous studies have implicated the human amygdala in fear- and threat-related processing. The animal images that elicited neuronal responses in the amygdala contained both aversive and cute animals, and we found no relationship between amygdala responses and either the valence or arousal of the animal stimuli."

In the end, they really don't have a satisfying explanation for what the amygdala, and even more interestingly only the right hemisphere's amygdala responds selectively to animals. 

"A plausible evolutionary explanation is that the phylogenetic importance of animals, which could represent either predators or prey, has resulted in neural adaptations for the dedicated processing of these biologically salient stimuli."

So basically they say, maybe neurons in the amygdala tell you 'this is animal-like, so pay attention' because of 'the evolutionary salience of animals'.  This might be true, but it's a pretty thin and un-meaningful explanation. 

It will be difficult to conduct more detailed experiments because these are human subjects with electrodes implanted in specific places for epilepsy monitoring.  That means, you are not going to be able to test what cells are synapsing onto these animal cells or where these cells send their signals.  But even with these limitations, interesting advances can be made by testing a wider variety of pictures to the subjects, to see how specific these cells can actually be.  (What if the animal is small and in the corner of a picture, where do babies or children fit in,  etc) 


© TheCellularScale

Mormann F, Dubois J, Kornblith S, Milosavljevic M, Cerf M, Ison M, Tsuchiya N, Kraskov A, Quiroga RQ, Adolphs R, Fried I, & Koch C (2011). A category-specific response to animals in the right human amygdala. Nature neuroscience, 14 (10), 1247-9 PMID: 21874014