The neocortex is argued to be the seat of cognition, but crows don’t have one.
The animals of neuroscience research are an eclectic bunch, and for good reason. Different model organisms—like zebra fish larvae, C. elegans worms, fruit flies, and mice—give researchers the opportunity to answer specific questions. The first two, for example, have transparent bodies, which let scientists easily peer into their brains; the last two have eminently tweakable genomes, which allow scientists to isolate the effects of specific genes. For cognition studies, researchers have relied largely on primates and, more recently, rats, which I use in my own work. But the time is ripe for this exclusive club of research animals to accept a new, avian member: the corvid family.
Corvids, such as crows, ravens, and magpies, are among the most intelligent birds on the planet—thelist of their cognitive achievements goes on and on—yet neuroscientists have not scrutinized their brains for one simple reason: They don’t have a neocortex. The obsession with the neocortex in neuroscience research is not unwarranted; what’s unwarranted is the notion that the neocortex alone is responsible for sophisticated cognition. Because birds lack this structure—the most recently evolved portion of the mammalian brain, crucial to human intelligence—neuroscientists have largely and unfortunately neglected the neural basis of corvid intelligence.
This makes them miss an opportunity for an important insight. Having diverged from mammals more than 300 million years ago, avian brains have had plenty of time to develop along remarkably different lines (instead of a cortex with its six layers of neatly arranged neurons, birds evolved groups of neurons densely packed into clusters called nuclei). So, any computational similarities between corvid and primate brains—which are so different neurally—would indicate the development of common solutions to shared evolutionary problems, like creating and storing memories, or learning from experience. If neuroscientists want to know how brains produce intelligence, looking solely at the neocortex won’t cut it; they must study how corvid brains achieve the same clever behaviors that we see in ourselves and other mammals.
While there have been a number of fascinating behavioral studies in corvids (especially from the lab of Nicola Clayton at the University of Cambridge) so far only Andreas Nieder, a neuroscientist at the University of Tübingen, has examined the neuronal activity of crows during sophisticated behavior. In Nieder’s first of such studies, published in 2013 inNature Communications, he and graduate student Lena Veit wanted to see what crows’ brains did when following an abstract rule.
In their experiment, Nieder’s team had the crows play an image matching game. The crows first had to briefly look at a sample image on a computer screen. Then, a cue indicated whether they should subsequently select the same (matching) image, or a different one, once the computer screen lit up again. Importantly, the cues for which image to select could be either visual (in this case, red or blue circles) or auditory (noise or glissando sound). The blue circle or glissando sound cued the crow to select the same image as appeared initially; the red circle or noise sound cued the different one. This required the crows to interpret the cue flexibly, since a sound or a visual could cue the same action.
Both crows and primates evolved to use the same computation, albeit through radically different machinery.
Once the birds learned the rule (they were rewarded with treats when behaving correctly), Nieder’s team began recording neuronal activity in the birds’ nucleus NCL (nidopallium caudolaterale), an area of the avian brain thought to be most like the mammalian prefrontal cortex (PFC), which enables decision-making, short-term memory, and planning for the future. (Eight microelectrodes were implanted in the birds’ brains during surgery.)
Examining the activity of over 300 neurons in two birds, Nieder’s team found that the crow’s NCL activity matched that of a primate’s prefrontal cortex: Both of the species’ neurons activated the most during the presentation of the rule cue, while activating much less in response to the images themselves. Some neurons responded specifically to the match cue (blue circle or glissando) and others to the non-match (red circle or noise); importantly, the neurons from each species activated in the same fashion regardless of the cue’s sensory modality (auditory or visual). Nieder’s results imply that both crows and primates evolved to use the same computation, albeit through radically different machinery, to solve the problem of representing abstract information—in this case, auditory or visual rules to a game…