Anaesthetised gerbils can still get down to a block-rocking beat, but would be left cold by Bob Marley’s reggae.
That’s the broad conclusion reached by a team of researchers that confirmed that beat perception, far from being a unique human trait, is likely strongly conserved in mammals.
Scientists led by Vani Rajendran of the Auditory Neuroscience Group at the University of Oxford in the UK set out to test whether low-level auditory processing contributed to beat perception.
In humans, the ability to respond rhythmically to beats has been long attributed to a complex process involving the coordination of sensory, motor and cognitive processes. Rajendran and colleagues, however, show that before these systems engage, midbrain processing may already be shaping how the brain responds.
To make their finding, the team anesthetised several gerbils and set them up to record the activity of their inferior colliculus, a major midbrain relay route that funnels information from the auditory nerve to the cerebral cortex.
The unconscious rodents were then exposed to seven rhythmic patterns constructed from pink noise. As a control, humans were also exposed to the rhythmic bursts and asked to tap along to them. (The humans were required to remain conscious, which is perhaps why the researchers used pink noise instead of, say, the music of Andre Rieu.)
In compiling the data gathered, the scientists discovered that the gerbils reacted most strongly to rhythms that were on-beat – that is, in a 4/4 system, where the emphasis is on the first or third beat of the bar, typical of much rock music. They reacted less strongly to rhythms with emphasis on the off-beat – the kind of second or fourth beat emphasis that defines reggae and ska music.
The team suggests the results indicate that the way humans perceive music may not be wholly a cultural matter, but may be constrained by simple brainstem processes.
“This observation is a demonstration of how the nature of high-level brain processes is often biased in its characteristics by ‘primitive,’ low-level features of the nervous system,” they write.