Male Songbirds Are High on Love
for National Geographic News
|October 3, 2008|
Male zebra finches could be addicted to love.
When wooing females, the Australian songbirds feel pleasure akin to that of a drug-induced high, a new study says.
In many animals, natural stimuli such as food and sex activate the brain's reward systems. In humans, drugs such as cocaine and amphetamines can produce the same effect.
When such strong signals are sent to the brain, neurons—or brain cells—can change in ways that cause addictive behavior.
When a human or animal is "rewarded," neurons in a part of the brain called the ventral tegmental area, or VTA, cause a flood of dopamine into other areas of the brain.
Dopamine is a powerful chemical messenger associated with feelings of desire, satisfaction, and happiness.
Increased activity in the VTA is a hallmark of addiction.
In the new study, Neal Hessler and Ya-Chun Huang of the RIKEN Brain Science Institute in Japan tried to determine whether natural rewards—such as birdsong—could also increase VTA activity.
Hessler and Huang found that the male birds' brains became flooded with dopamine when they sang to females, but not when they sang for themselves.
The research is detailed online in the journal PLoS One.
(Related: "Smell May Play Role in Bird Courtship, Study Finds" [May 27, 2003].)
The finding "is the most direct evidence so far that the same brain circuits that are related to reward in mammals are activated while males serenade female birds," Hessler said.
Birds and mammals have not shared a common ancestor for tens of millions of years, so the notion that the reward systems in both groups function similarly suggests the mechanism is a very ancient one.
"I expect these areas should have been present in dinosaurs, too," Hessler said.
Hessler also suspects that female birds may be experiencing a kind of parallel reward effect in their own brains when they're being courted.
"Females are the ones who make the important decision after hearing a male sing," Hessler said. "I expect that they should have increases of VTA activity and dopamine when they like a male's song."
Implications For Humans
The new findings suggest addiction in humans is more complicated than previously thought.
The conventional view has been that human addiction was partly due to a disruption in the brain's VTA system.
"Here we showed that even natural rewards can cause similar changes in reward system function, at least temporarily," Hessler said.
It's possible that addiction involves a kind of reward imbalance, whereby naturally rewarding stimuli become less potent compared to an addictive drug, he added.
Kent Berridge is a neuroscientist at the University of Michigan-Ann Arbor who was not involved in the study.
Berridge said the finding helps shed light "on the natural origins of the dopamine system, and reveals what dopamine originally evolved to do.
"It helps put what is known about brain mechanisms of addiction into a larger neuropsychological and evolutionary context," he added.
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