AUTUMN 2008/VOLUME 22, NUMBER 4
Birds Change Their Minds—Literally
Our changing understanding of bird brains
Imagine replacing obsolete memories with new information—erasing old song lyrics, outdated phone numbers, and useless facts, to make room for what you need to remember now. Through a process known as neuronal replacement, chickadees and some other birds do just about exactly this.
Once a neuron contains a long-term memory, it is permanently altered, no longer able to be used in circuits involved in new memory formation. Long-lived, small birds apparently allow neurons containing old information to die, replacing them with new neurons so they can adapt to changes in their social flocks and environment even with their tiny brains.
In a landmark study published in 1996, researchers at the Rockefeller University found new neurons in the chickadee hippocampal complex throughout the year, peaking in October.
During late summer and early fall, chickadee diets switch from mostly insects to mostly seeds, and birds start storing seeds. New spatial memories formed in the hippocampus are crucial. Tests conducted on both wild and captive chickadees showed that wild birds, with a greater need to remember new food caches, replaced many more neurons.
In a 2002 study, researchers from the University of California at Davis and the University of Cambridge found that chickadees from Alaska have a larger hippocampus than those from less harsh environments in Colorado. Alaskan chickadees store more food and remember hiding places more easily.
Another species, the domesticated canary, replaces neurons in a region of the brain called the high vocal center, where songs are developed, according to a study by researchers from Wesleyan University. Every fall, male canaries alter their songs, and alter them again at the start of a new breeding season. Peaks in neuronal replacement correlate with times of song modification.
When canaries breed, males sing stereotyped songs, repeating notes and phrases. As the breeding season closes, adult males sing unstable songs similar to those of young males just learning to sing. This period of instability coincides with marked neuron death in the high vocal center. When new neurons replace older ones, the canaries once again sing stable songs, but the song patterns are now different. Thanks to neuron replacement, they sing a unique song each breeding season.
Scientists continue to study captive and wild birds to further their understanding of neuronal replacement, its influences on avian behavior, and implications for human medicine.
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