Gerbils count the beat, unconsciously
Beat perception may not be just a high-level brain function as thought.
Anaesthetised gerbils can still dig a blockrocking beat, but would be left cold by Bob Marley’s reggae. That is the broad finding of research that suggests while conscious beat perception is extremely rare in the animal kingdom, it may exist at an unconscious level in mammals.
Only a few species apart from humans have shown the ability to keep a beat – the select list includes cockatoos, bonobos and sea lions.
In humans the ability to respond to beats has long been attributed to a complex process involving the human brain’s sophisticated outer layer, the cortex, coordinating with sensory and motor input. However, in findings published in the Proceedings of the Royal Society B, Vani Rajendran and colleagues, at the University of Oxford, show that before these systems engage, the more primitive midbrain – which relays sensory input to the cortex – may already be shaping the response.
To make their finding, the team anaesthetised several gerbils and recorded 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 exposed to seven rhythmic patterns. As a control, the same patterns were played to human subjects who remained conscious and were asked to tap along.
The scientists report 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 on the off beat – the kind of second or fourth beat emphasis that defines reggae. The team suggests the results indicate the way humans perceive music may not be wholly a cultural matter, and is constrained by more primitive brain processes.