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.
A new study, however, by researchers at the University of California, San Diego School of Medicine finds that a comparable region in the brains of chickens concerned with analyzing auditory inputs is constructed similarly to that of mammals.
"And so ends, perhaps, this claim of mammalian uniqueness," said Harvey J. Karten, MD, professor in the Department of Neurosciences at UCSD's School of Medicine, and lead author of the study, published this week in the Proceedings of the National Academy of Sciences Online Early Edition.
Generally speaking, the brains of mammals have long been presumed to be more highly evolved and developed than the brains of other animals, in part based upon the distinctive structure of the mammalian forebrain and neocortex – a part of the brain's outer layer where complex cognitive functions are centered.
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.
"The belief that cortical microcircuitry 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," said Karten.
"Animals like birds were viewed as lovely automata capable only of stereotyped activity."
But this kind of thinking presented a serious problem for neurobiologists trying to figure out the evolutionary origins of the mammalian cortex, he said. Namely, where did all of that complex circuitry come from and when did it first evolve?
Karten's research supplies the beginnings of an answer: From an ancestor common to both mammals and birds that dates back at least 300 million years.
The new research has contemporary, practical import as well, said Karten. The similarity between mammalian and avian cortices adds support to the utility of birds as suitable animal models in diverse brain studies.
"Studies indicate that the computational microcircuits underlying complex behaviors are common to many vertebrates," Karten said. "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."
The research was supported by grants from the National Institute of Neurological Disorders and Stroke, the National Institute of Mental Health and the National Institute on Deafness and Other Communications Disorders.
Additional contributors include Yuan Wang of UCSD Department of Neurosciences, the Virginia Merrill Bloedel Hearing Research Center, University of Washington, Seattle and Agnieszka Brzozowska-Prechtl of the UCSD Department of Neurosciences.
Scott LaFee | EurekAlert!
Smart Data Transformation – Surfing the Big Wave
02.12.2016 | Fraunhofer-Institut für Angewandte Informationstechnik FIT
Climate change could outpace EPA Lake Champlain protections
18.11.2016 | University of Vermont
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water
In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...
The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.
Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
02.12.2016 | Medical Engineering
02.12.2016 | Agricultural and Forestry Science
02.12.2016 | Physics and Astronomy