Bird Brains Aren’t That Simple!
We often taunt others about being a “bird brain” with the connotation that they are stupid or scatter brained! Why have we thought that, and why might science now suggest that … well, a bird brain just might be … “brainy!”
It all started when we humans compared the smooth-surfaced brain of birds to that of mammals. Reptiles and birds have a smooth-surfaced brain termed a lissencephalic brain. As we look at the surface of the brains of mammals, we see that those brains contain convolutions. These convolutions are called gyri (the rounded parts) and the sulci are the fissures between. And when we look at the numbers of convolutions we find that they increase significantly with primates and humans.
This finding led scientists to suggest that those animals that do not have convolutions (i.e., reptiles and birds), must have a simpler brain capacity, operating more at a reflex level without the capacity to think like those species with convolutions. And the corollary would be that as the numbers of gyri and sulci increase, the cognitive abilities of that species would also increase. The thinking was that there was an evolutionary development so that reptiles came first, then birds arrived with added parts to the nervous system, which laid the foundation for the more complex brain of mammals — leading to the ultimate brain with its significantly increased convolutions — humans!
But there are cracks in that theory of “brain power,” so to speak, and I previously reported on the theory of sociality and intelligence. The conundrum was created by a series of studies beginning in the previous decade that directly compared the cognitive abilities of parrots and crows with those of primates. The studies found that the birds could manufacture and use tools, use insight to solve problems, make inferences about cause-and-effect relationships, recognize themselves in a mirror and plan for future needs, among other cognitive skills previously considered the exclusive domain of primates.
It was recognized that those bird species that are highly social like parrots and those that live in large flocks need greater intelligence to maintain that social structure, intelligence that also helps them solve those puzzles that scientists created for them. This created quite a problem for scientists to explain — how could they do that without those darn convolutions?
When comparing areas of the forebrain of birds and mammals, birds did not have more space but less space. The forebrain is the area of the brain that can think into the future. The forebrain is also called the prosencephalon, the region of the developing vertebrate brain. This forebrain includes the telencephalon, which contains the cerebral hemispheres and those are the convolutions. Under these, are the other regions – the diencephalon, which contains the thalamus, hypothalamus, epithalamus, and subthalamus. The forebrain plays a central role in the processing of information related to complex cognitive activities, sensory and associative functions, and voluntary motor activities. It represents one of the three major developmental divisions of the brain; the other two are the midbrain and hindbrain.
Well this past month, scientists who have been working on this conundrum have advanced the reason that birds have solved the problem of complex intelligence without gyri and sulci. The study was published in the National Academy of Sciences and here is the reference if you would like to read it in detail:
Proc Natl Acad Sci U S A. 2016 Jun 28;113(26):7255-60. doi: 10.1073/pnas.1517131113. Epub 2016 Jun 13. Birds have primate-like numbers of neurons in the forebrain. Olkowicz S1, Kocourek M1, Lučan RK1, Porteš M1, Fitch WT2, Herculano-Houzel S3, Němec P4.
It appears that the part of the brain that corresponds to the forebrain, the pallium in birds, has a much higher concentration of neurons or the brain cells packed in the same amount of space than many primates. These scientific colleagues studied the brains of 28 species, including the blue-and-gold macaw, African grey parrot, Goffin’s cockatoo, cockatiel and budgerigars, and all of them had more cells in that forebrain area per mass than mammals, including some of the primates. For example, the blue-and-gold macaw had more neurons than the macaque even though the macaque brain is larger and has those convolutions.
“We found that birds, especially songbirds and parrots, have surprisingly large numbers of neurons in their pallium: the part of the brain that corresponds to the cerebral cortex, which supports higher cognition functions such as planning for the future or finding patterns. That explains why they exhibit levels of cognition at least as complex as primates,” said Herculano-Houzel, who recently joined the Psychology Department at Vanderbilt University in Nashville, Tennessee.
That is possible because the neurons in avian brains are much smaller and more densely packed than those in mammalian brains, the study found. Parrot and songbird brains, for example, contain about twice as many neurons as primate brains of the same mass and two to four times as many neurons as equivalent rodent brains. This could potentially provide the basis for their cognition that rivals primates.
One of the important implications of the study, the neuroscientist said, is that it demonstrates that there is more than one way to build larger brains. Previously, neuroanatomists thought that as brains grew larger neurons had to grow bigger as well because they had to connect over longer distances. “But bird brains show that there are other ways to add neurons: keep most neurons small and locally connected and only allow a small percentage to grow large enough to make the longer connections. This keeps the average size of the neurons down,” she explained.
This study opens up many questions regarding the brains of birds. One is that with all of those brain cells, does it require more energy to run the brain in birds compared with mammals? Why would this system of small cells be better for birds that fly? Even the emu had more cells in the pallium compared with mammals of similar brain size. Why did the mammal brain diverge using a different system? These and other questions are very exciting. But it just verifies to bird owners what we already knew in part — bird brains are not that simple and we know now that is because they have a large number of small neurons packed in their forebrains!