Are you smarter than a rabbit?
You probably feel that you are. But in what way, exactly? Neuroscientists Laurel Carney and colleagues report that the rabbit brain is curiously inefficient – and hypothesize that the human brain is better: Suboptimal Use of Neural Information in a Mammalian Auditory System
Carney et al found that rabbits are not very good at hearing a certain feature of sounds, called amplitude modulation. Rabbits trained to tell the difference between modulated and unmodulated sounds (earning a tasty food pellet for correct answers) could only succeed when the degree of modulation is quite high. Humans can detect much weaker modulation.
By itself, this might just mean that rabbits’ ears aren’t as good at picking up these stimuli than ours. But Carney et al crucially found that the rabbits’ brain does in fact encode the information needed to perform as well as humans.
Using recording electrodes, they found that the rabbit’s inferior colliculus IC does respond to amplitude modulation at the low level that humans can perceive. The IC does so in a rather subtle way, however, the presence of modulation causing differences in the timing (synchrony) of cell firing.
Only at higher levels of modulation do cells in the IC start to respond to modulation in terms of the overall rate of firing. Rabbits seem to be able to hear this. These graphs show the result: the top of the graph shows less modulation, i.e. a more difficult task.
The black line shows human behavioral performance while the lower, i.e. worse, grey line is rabbit. The blue dots show the firing rate response of individual rabbit IC cells to modulation; you can see that the most sensitive cells correspond pretty well to rabbit behavioral performance.
But the red dots show that many rabbit cells were much more sensitive to modulation than this – if you consider the synchrony of their firing. The best rabbit cells were, paradoxically, better at the task than the rabbits themselves, and approached human performance.
This raises the fascinating idea that the reason we’re better than rabbits at hearing amplitude modulation is that our brains can make better use the same neural information – that somehow, we can translate neural synchrony into behavior while rabbits can’t (in this instance.)
However, this is all hypothetical, because Carney et al didn’t record from the human inferior colliculus. It might be that we rely on firing rate, not synchrony, just the same as rabbits, with our IC just responding with altered firing rates more readily. Carney et al write that this is unlikely, but they can’t rule it out.
Still, assuming that we are better at making efficient use of neural information, could this be a general explanation for why humans seem to be smarter than rabbits – or, indeed, other animals? Could this underpin ‘Human Uniqueness’? Probably not (and the authors are certainly not saying that.) But it’s certainly a thought-provoking paper.
Laurel H. Carney, & et al (2014). Suboptimal Use of Neural Information in a Mammalian Auditory System Journal of Neuroscience DOI: 10.1523/JNEUROSCI.3031-13.2014
