Washington, Oct 4 : Singing for female birds triggers 'happy' feelings in males' brain - an effect which is quite similar to the euphoric state that a person experiences under the influence of addictive drugs - says a new study.
Researchers at the RIKEN Brain Science Institute in Japan have demonstrated that when male birds sang to attract females, specific "reward" areas of their brain were strongly activated, and addictive drugs also found to cause similar strong brain activation.
Human and animal brains are programmed to have a positive emotional response to rewarding stimuli, such as food or sex. A critical part of this reward signal is apparently provided by increased activity of neurons containing dopamine in the brain ventral tegmental area, VTA.
Along with natural rewards, the same brain circuits can also be strongly activated by artificial rewards such as addictive drugs.
In earlier studies in mammals, it was found that after animals are given drugs such as cocaine or amphetamine, the strength of synaptic connections onto dopamine neurons in VTA is strongly increased, or potentiated. Such potentiation has been suggested to be an important long-lasting adaptation of brain function caused by drug use, and involved in maintenance of addictive behaviour.
In the study, Ya-Chun Huang and Neal Hessler of the Vocal Behaviour Mechanisms Lab examined a specific social behaviour- courtship singing of songbirds.
They analysed the zebra finch, an Australian songbird, where males sing in two different situations. Most importantly, males sing "directed song" during courtship of females. When males are alone, they produce "undirected song", possibly for practice or to communicate with birds they can't see.
In an earlier study, it was seen that only when males sang to attract a female, and not when they sang while alone, many unidentified neurons in the VTA were strongly activated.
In the new study, researchers have shown that such a natural social interaction, singing to a female, can cause the same kind of synaptic potentiation of VTA dopamine neurons as use of addictive drugs, while singing solo did not affect these neurons.
A closer look into the system may give insight into how both natural and artificial rewards interact with each other, and specifically how damage to brain reward systems during addiction can disrupt processing of natural rewards such as social interaction.
This study also provides the clearest evidence so far that singing to a female is rewarding for male birds. This may not be surprising, as such courtship is a necessary step in producing offspring, and so should be a positive experience.
Other studies have provided some evidence that in mammals, including humans, sexual behavior and attachment (as well as rewarding aspects of video games and chocolate) also depend on the same brain reward areas and dopamine.
Thus, despite the distant evolutionary relationship between birds and humans, it may be that during such intense social interactions as courtship, both share some similar emotional state.
The study is published in the online, open-access journal PLoS ONE.