This is actually an old article, published in Music Perception's Winter 2003 issue. But the title is great, and it's on my mind because I had my seminar students read the article and prepare a group presentation on it. (Their last writing assignment is to prepare a script for a 10-minute presentation on a research article about music and science.) The title of the article is "Do Rats Show a Mozart Effect?" by Kenneth M. Steele. The article examines the results of another article, "Improved maze learning through early music exposure in rats," in Neurological Research, 20 (1998). This earlier article is by the grandmother of the Mozart Effect, Frances Rauscher (with co-authors). She first claimed that listening to Mozart's Sonata for Two Pianos in D major, K 448 increased spatial reasoning in 1993. This claim sparked all sorts of Mozart for Baby products as parents hoped to make their wee ones geniuses merely by playing some classical music to them. Music educators also hopped on the bandwagon, using the results to justify more support for music programs in schools. Recent studies by one of Rauscher's associates have attempted to generalize the Mozart effect to Alzheimer patients and epileptic patients. Alzheimer patients listening to Mozart did better on a visual-spatial task; epileptic patients had fewer seizures, even if in a coma!
The problem is, laboratories that attempt to replicate the Mozart Effect are more likely to fail than succeed. Steele cites twelve studies that failed to produce the result, and two that did produce the effect. The two positive results have been explained by arousal or preference differences, not priming of the spatial reasoning parts of the brain. In efforts to counter the claim that any Mozart effect is caused by arousal (liking the music), Rauscher and some colleagues showed the Mozart effect in rats. As rats do not share our cultural preferences, any effect must be neurophysiological.
Rats were bred in the presence of a repeating loop of the Mozart sonata, Philip Glass's Music With Changing Parts, or white noise. Pregnant rats were exposed to one of these conditions for 12 hours each day through gestation. The birthed rats were exposed to the sound for another 60 days. Then the rat pups were run through a maze. Groups were trained on the maze with one of the sounds present, so some were exposed to the same sound but other groups were exposed to a different stimulus. The Mozart-reared group did best in learning the maze, regardless of what music was played. Sounds good, right?
The problem is, rats are born deaf. They cannot perceive any air-borne sounds until 11 days after birth, and no skull-conducted sounds until 7 days after birth. So no sound signals were reaching the rat fetuses, and no sounds for the first week of the 5 week testing. But the rats do get 4 weeks of sound, and the mothers could be affected, right? Well, rats hear frequencies effectively between 8,000 Hz and 32,000 Hz. The entire piano keyboard ranges from 27.5 Hz to 4186 Hz, so even the highest piano note is below the rat's threshold of perception. Even at the loud levels of the study (65-70 dB) the rat could perhaps hear some notes within the piano range, but only about 1/3 of the notes of the Mozart sonata assuming no masking effects of noise from ventilation fans and computers.
Steele claims that the "effect" on the rats was a litter effect, genetic disposition of the rats, as all the Mozart-reared rats came from the same mothers. He also points out other questionable procedural methods of Rauscher's group, choosing groups with no blinding procedures to keep scientist bias out. So the answer is, rats do not show the Mozart effect. Thus, any observed Mozart effect in humans (which is still controversial at best) is still best explained by arousal rather than brain re-wiring.
Update: Rereading this, I decided to point out that Rauscher has responded well to her critics. She emphasizes active music making over passive listening for any cognitive improvements. And Rauscher did not make outlandish claims of boosts to IQ in her reports. Newspapers misused her research (no surprise there), as did music educators and various companies. Rauscher only claimed an effect on the cognition of spatial relations. I also found out after writing this post that Frances Rauscher is an accomplished cellist as well as psychologist. She has a bachelor's degree in performance from Julliard, and even soloed with the National Symphony Orchestra. (bio here) And finally, while I think Steele has pointed out some serious flaws to Rauscher's research methods, I don't think he has completely disproven the legitimacy of the Mozart effect either.