The brains of birds


ScienceDaily reports on work by Y. Wang and others (here) which compares the mammalian neo-cortex with structures in the brains of birds.

For more than a century, neuroscientists believed that the brains of humans and other mammals differed from the brains of other animals, such as birds (and so were presumably better). This belief was based, in part, upon the readily evident physical structure of the neocortex, the region of the brain responsible for complex cognitive behaviors.

Specifically, the mammalian neocortex features layers of cells (lamination) connected by radially arrayed columns of other cells, forming functional modules characterized by neuronal types and specific connections. Early studies of homologous regions in nonmammalian brains had found no similar arrangement, leading to the presumption that neocortical cells and circuits in mammals were singular in nature.

For 40 years, Karten and colleagues have worked to upend this thinking. In the latest research, they used modern, sophisticated imaging technologies, including a highly sensitive tracer, to map a region of the chicken brain (part of the telencephalon) that is similar to the mammalian auditory cortex. Both regions handle listening duties. They discovered that the avian cortical region was also composed of laminated layers of cells linked by narrow, radial columns of different types of cells with extensive interconnections that form microcircuits that are virtually identical to those found in the mammalian cortex.

The findings indicate that laminar and columnar properties of the neocortex are not unique to mammals, and may in fact have evolved from cells and circuits in much more ancient vertebrates.

This has several ramifications. In vertebrates, different species have brains that differ more in degree and less in kind and therefore simpler brains may be very useful experimental subjects. They may be easier to work with by still give valuable insights. It also weakens the taboo on anthropomorphism. If it acts like cognition – it may be cognition. And finally there is nothing like two different examples of the same principle to find the important aspects of the principle. In trying to understand how the neo-cortex module functions it is useful to have the mammal and bird versions to compare. And consciousness need not be thought of as strictly a mammal thing just because in mammals it involves the neo-cortex.

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