Mouse songs

Gourbal et al (2004) discovered that mice "sing", or produce ultrasonic vocalizations (USV), that are not audible to humans. Specifically, male mice sing during mating, and female mice sing during same-sex social interaction. Holy and Guo (2005) demonstrated that the presence of female pheromones alone was enough to induce singing in males. Further investigations (e.g. Wang et al, 2008) demonstrated that female mice did not respond similarly to the presence of males or their pheromones.

Panksepp et al (2007) tied differences in USV to both genetic and behavioral differences: juvenile mice who sang more were likely to engage in more "social investigation" with cage-mates. Panksepp's experimental mice (which sang less) were bred missing a gene that forms part of the dopamine circuit, and so it is believed that mice produce USVs when they are happy or experiencing pleasure. The sounds produced by females during mating are human-audible squeaks with a very different profile than USVs.

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The general idea of these studies is that social pleasure - such as greeting friends - uses the same neural reward system as sex or drugs. Male and female mice seem to get these rewards from different circumstances. I find myself thinking about the rhetoric of the so-called "War on Drugs". In junior high, we were told that drugs replace everything else that makes you happy. Spending time with your friends, playing sports, etc, wouldn't make you happy anymore if you were an addict, because only the drug would make you happy. Now, I don't know about that for drugs, but I wonder if something like that applies for sex where males are concerned. It looks, from these studies, as if juvenile male mice sing when playing with other mice, but adult male mice don't. It's tempting to make similar generalizations about humans.