Bird brains shown more advanced than name implies
Feb. 8, 2006Contact Information:
Dr. Wayne Kuenzel, Department of Poultry Science
479-575-6112 / wkuenzel@uark.edu
By Fred Miller, University of Arkansas Division of Agriculture
479-575-5647 / fmiller@uark.edu
Dr. Wayne Kuenzel with digitized images mapping structures of the chicken brain.
Dr. Alexander Jurkevic of Viulnius, Lithuania, visiting professor of poultry science, and Ph.D. student Hongyan Li of Beijing, China, use a cryostat to slice frozen chicken brains into thin slices for research.
FAYETTEVILLE, Ark. — The term “bird brain” doesn’t mean what it used to.
The avian brain is more advanced than was once thought, said Dr. Wayne Kuenzel, poultry neurobiologist for the University of Arkansas Division of Agriculture. The traditional nomenclature for many of the brain structures, developed nearly a century ago and based on early misconceptions, no longer makes sense, he said.
Kuenzel was part of an international consortium of neuroscientists who have proposed renaming the structures of the avian forebrain, thereby correcting the scientific nomenclature and giving birds their due.
Appropriate naming is important to Kuenzel because he studies poultry brain structures to determine sites that are important for specific functions such as reproduction and courtship behavior. For example, he is locating nerve cells in chick brains that respond to light in terms of recognizing seasons.
“Many birds are photoperiodic,” Kuenzel said. “Their physiological systems respond to changes in the length of daylight.”
His research locates these cells in the brain and determines how they may work.
“These are the very first nerves in a cascade of neural pathways that activates the reproductive system,” Kuenzel said.
Down the road, such information could help determine which birds will have reproductive systems that are most responsive to changes in light. This would be a valued trait in commercial breeder flocks, he said.
His work in avian brain structures and functions led Kuenzel to participate in the Avian Brain Nomenclature Forum. The group began with a meeting in 2002 organized by Duke University neurobiologist Erich Jarvis and University of Tennessee Health Science Center neuroanatomist Tony Reiner. The National Science Foundation and the National Institutes of Health funded the forum’s efforts.
The group concluded, in a paper published in Nature Reviews Neuroscience in 2005, that birds are similar to mammals in cognitive ability. The new nomenclature was developed to provide consistency in language between mammalian and avian neuroscientists. Kuenzel, one of 29 co-authors of the paper, said the terminology is coming into use progressively as researchers adopt it.
Under the old model, the forebrain was believed to be mostly basal ganglia, a structure that controls motor function, Kuenzel said. Most structures within the forebrain were assigned names ending in the suffix “striatum” to signify the major tissue type found in the basal ganglia.
The old model suggests that birds never developed a cortex, that area of the brain in mammals in which thinking, learning and memory take place.
“This suggested that there was no cortical-like tissue, which would mean birds had no repertoire of behavior that could be learned,” Kuenzel said. “It suggested they have extraordinary motor function but that behavior is largely instinctive.”
Despite this, Kuenzel said, behaviorists have reported for many years that birds do learn, everything from the songs of songbirds to how to use tools. “And they have good memories,” he said. “They can find seed that they’ve hidden away, and some return to a nest site where they were born the previous year when they migrate north to breed.”
Kuenzel said birds do not have a cortex like humans and other mammals, but they do have cortical-like tissue. “It’s just organized differently,” he said.
By definition, a true cortex requires a structure of six layers of cells. But scientists learned that bird forebrains have considerable amounts of cortical-like clusters of cells covering over the basal ganglia, Kuenzel said.
This structure has been verified repeatedly by powerful chemical and molecular techniques that verify the type of cell and the organization of neural structures, and suggest how they work, Kuenzel said.
For example, he said, tract-tracing allows scientists to trace the pathways from sensory perception, such as light entering the eyes, to the processing centers of the brain where images are analyzed and action taken.
Since the avian forebrain does not contain a true cortex, the scientists settled on “pallium” as the proper term to denote this tissue, Kuenzel said. Pallium denotes a cortical-like brain region. In the new terminology, it replaces the former suffix “striatum” in many forebrain structures.
“Proper nomenclature clears up communication between avian scientists and those studying other vertebrate species,” Kuenzel said. “It also facilitates the use of birds in behavioral studies of learning and cognition.”