The aim of the study was to determine if cats were able to process auditory stimuli even though they were anesthetized. They evaluated two parameters, respiratory rate and pupil diameter. These parameters are affected by the depth of anesthesia; as you come out of anesthesia, your respiratory rate increases and your pupils get larger. Deeply anesthetized animals have a slower respiratory rate and smaller, constricted pupils.
Twelve cats that were scheduled to be spayed were fitted with little kitty cat headphones that completely covered their ears, and were exposed to 2 minute excerpts of music representing three different genres - classical, pop, and heavy metal at three different times during their surgery. A medical monitor measured the heart rate. and digital calipers measured the pupil diameter.
The results weren't surprising, really. Cats showed nice low respiratory rates and small pupils when played classical music. The values were intermediate for pop music. Heavy metal caused a faster respiratory rate and larger pupils.
The conclusion: cats under general anesthesia do indeed process auditory stimuli. So, depending on the type of music being played in the surgery room, the anesthesiologist may be able to administer a reduced anesthesia dose, minimizing undesirable side effects.
I checked the "materials and methods" section to see exactly what the researchers used as representative of the genres. Their classical choice was Samuel Barber's Adagio for Strings (Opus 11). The pop sample was "Torn" by Natalie Imbruglia. For heavy metal, they used "Thunderstruck" by AC/DC.
I'm trying to envision a cat, under anesthesia, with over-the-ear headphones, being forced to listen to Natalie Imbruglia. Doesn't this violate animal cruelty laws?