Saturday July 03, 2010
Birdbrained:
Humans & Chickens Share Brain Structure
by Simon Magus
Neuroscientists have traditionally believed that the brains of humans and other mammals differ from the brains of other animals, such as birds.
This so-called received wisdom has prevailed for over a century -- but a new study conducted at the University of California in San Diego (UCSD) shows that a region in the brain of a chicken concerned with analysing auditory input is similar to that of a comparable region in mammals.
"And so ends, perhaps, this claim of mammalian uniqueness," said Professor Dr Harvey J. Karten of UCSD's School of Medicine, lead author of the study.
Mammalian brains were presumed to be more highly evolved and developed than the brains of other animals, in part based upon the distinctive structure of the forebrain and neocortex.
The mammalian neocortex features layers of cells (lamination) connected by radially arrayed columns of other cells.
Early studies of nonmammalian brains had found no similar arrangement, leading to the assumption that neocortical cells and circuits in mammals were unique.
"The belief that cortical micro-circuitry was a unique property of mammalian brains was largely based on the lack of apparent lamination in other species, and the widespread notion that non-mammalian vertebrates were not capable of performing complex cognitive and analytic processing of sensory information like that associated with the neocortex of mammals," Professor Karten said.
"Animals like birds were viewed as lovely automata capable only of stereotyped activity."
But this view created a serious problem for neurobiologists trying to figure out the evolutionary origins of the mammalian cortex -- where did all of that complex circuitry come from and when did it first evolve?
Professor Karten now believes that the answer lies with a common ancestor to both mammals and birds dating back at least 300 million years.
The similarity between mammalian and avian cortices points towards birds as suitable animal models in diverse brain studies.
"Studies indicate that the computational microcircuits underlying complex behaviours are common to many vertebrates," said Professor Karten.
"This work supports the growing recognition of the stability of circuits during evolution and the role of the genome in producing stable patterns."
"The question may now shift from the origins of the mammalian cortex to asking about the changes that occur in the final patterning of the cortex during development."
Image credit: John Went / CC BY-SA 2.0
Posted in: Science by bubblejam at 05:49 PM | Comments (0) | Email This Entry