Mental and behavioural attributes are notoriously difficult to quantify, whether one is speaking of an individual or population. While there are specific well qualified claims that can be made about intellectual abilities or behavioural adaptability, any sort of general sweeping statement about the ‘uniquely human trait of…’, though rife within popular and scientific literature from psychology or neuroscience, tend to crumble under close scrutiny. Making such an unqualified statement irks me, as I believe it fosters an undue reverence for the human brain (despite our heavy reliance on model organisms for neuroscience research), and is reminiscent of Descartes’ baseless theological labeling of all non-humans as mindless automatons. Of course, I am not suggesting that there are not unique or laudable aspects of our species’ cognitive abilities (for example, our penchant for complex linguistic communication is quite impressive, but in no way is communication or even language a uniquely human endeavour. Human language is a unique and impressive cognitive trait that has helped enable our species to accomplish some truly impressive feats, but nailing down just what exactly makes our language quintessentially human (other than being used by humans) is astonishingly difficult). The difficulty of making cross-species generalizations is further compounded by our inability to break away from our own human perspective. In the same way that we must be careful not to incorrectly attribute cognitive abilities and methods to non-humans through overly zealous anthropomorphism, we must be wary of missing the abilities of other animals through the sheer alien nature of the abilities (for example, while we are now quite comfortable with the idea of bats utilizing echo-location to navigate and hunt, when sonar was a top-secret military technology it was a startling and preposterous revelation).
Given the sloppiness of such ‘uniquely human’ generalizations, therefore, I was quite astonished to see a ScienceNOW article not only referencing Descartes in the first sentence but following it with the question, “What imbues us with this uniquely human sense of self-awareness?” The news brief, written by Greg Miller, is apparently based on a paper in Nature Neuroscience1 (I say apparently because I was unable to find an explicit reference). Reading through the paper itself, I noticed no such sentiments. Rather, the paper served as a brief and informative summary of a study on interoceptive awareness using a comparison test of heartbeat sensation in a brain lesion patient and uninjured control subjects. Greg Miller does a perfectly fine job of summarizing the actual methods and results of the paper in the rest of his news brief, so I will not dwell on those here. I simply take issue with his opening lines.
The definition of self-awareness is itself a matter of some contention, but in the sense that this study comments upon (awareness of changes in visceral function) I find it bizarre that anyone would even contend such a sense was uniquely human. After all, rat behaviour will markedly change following an injection of cortisol2 despite cortisol’s extremely low penetration of the blood-brain barrier3. Interestingly, in Vinogradova and Zhukov’s paper2 the behavioural response to cortisol injections was often of an opposite nature in two different breeding strains that were selected for high or low rates of acquiring active avoidance behaviour. Such differences are at least plausibly suggestive of an ambiguity in the interpretation of visceral changes brought on by the cortisol injection, similar to the famous ambiguity between fearful and lustful physiological arousal demonstrated by Dutton and Aron4. With two populations bred for opposite learning tactics from fearful stimuli, it is reasonable they would also exhibit a change in their likelihood of interpreting a shift in physiological state as anxiety (which is to a large extent the expectation of fear and horror in the near future).
Moving beyond the self awareness of what is going on within one’s own body to more abstract notions of the self, the mirror test is a classic tool for exploring the subject (although I have my own reservations on the efficacy of the mirror test, those can be saved for another time). Just four short days after Greg Miller claimed that only humans were self-aware, another ScienceNOW news brief came out describing the success of pigs at learning to use a mirror to find food, a measure which, in the words of the lead author Donald Broom, gives pigs at least “some degree of self-awareness”. The article also conveniently provides a list of other animals who have passed the mirror test: elephants, dolphins, magpies, gray parrots, and some primates (including humans, which the article for some reason listed separately).
While sweeping statements on human uniqueness are appealing to both our species’ vanity and as a nice opening line to elevate the profundity of the topic at hand, they are misleading and not backed up by evidence. Such language does a disservice to the field of neuroscience and discounts the contribution of model neurological organisms and comparative neuroanatomy to our understanding of the brain and its function.
1 Khalsa, Sahib S., David Rudrauf, Justin S. Feinstein, and Daniel Tranel. 2009. The pathways of interoceptive awareness. Nature Neuroscience, Advanced online publication.
2 Vinogradova, E. P. and D. A. Zhukov. 2008. Changes in anxiety after administration of cortisol to rats selected for the ability to acquire active avoidance. Neuroscience and Behavioral Physiology, 38:781-783.
3 Pardridge, William M. and Lawrence J. Mietus. 1979. Transport of steroid hormones through the rat blood-brain barrier. The Journal of Clinical Investigation, 64:145-154.
4 Dutton, D. G. and Aron, A. P. 1974. Some evidence for heightened sexual attraction under conditions of high anxiety. Journal of Personality and Social Psychology, 30:510-517.