Human brain has dedicated set of nerve cells that respond only to sound of music, study finds

If music be the food of love then it is a pretty universal diet appreciated by all cultures and societies throughout history – and now scientists are beginning to understand why.

A pioneering study has found that the human brain has a dedicated set of nerve cells that respond only to the sound of music, which contradicts the widely accepted view that musical appreciation is merely “piggybacking” on the ability to hear other everyday sounds such as speech.

The researchers used a sophisticated way of analysing the data gathered by medical brain scanners while a group of people listened to different kinds of sounds.

Scientists found that one particular set of neurons in the auditory cortex of the brain fired their electrical impulses only when the participants in the experiment were listening to music.

Although the findings will need further investigation, the results could support the idea that there is a dedicated centre or “music box” in the brain which has evolved to appreciate a melodious tune or vibrant rhythm.

Previously, researchers had thought that appreciating music was a side-effect of being able to detect and decipher other complex sounds, such as speech. However, the new study suggests music may even have played a role in the evolution of the human brain.

Josh McDermott, an assistant professor of neuroscience at the Massachusetts Institute of Technology said: “We found evidence for a population of neurons in the adult human brain that responds selectively to music. The experiments also revealed a separate population that responds selectively to speech.

“In both cases the responses were strikingly selective – the neural response is strong when people listen to music, in one case, or speech, in another, and much less strong to every other type of sound that we tested.”

He said the two groups of neurons were in different parts of the auditory cortex – the part of the brain that processes sound, “suggesting the existence of separate pathways in the brain for the analysis of music and speech”.

The study, published last week in the on-line journal Neuron, involved exposing 10 volunteers to 165 different sounds, including segments of speech and fragments of music, as well as everyday sounds such as footsteps, a car ignition or a ringing telephone.

Their brain activity was simultaneously monitored by a functional magnetic resonance imagining (fMRI) machine, which measures blood flow as a marker of neural activity. Using a sophisticated method of analysing the fMRI data, the scientists were able to identify six different populations of nerve cells in the auditory cortex that each responded in a unique way to different sounds, including music.

What is still not clear, however, is whether people are born with “musical neurons” or whether nerve cells develop a “taste” for music during childhood development.

“Our results suggest the presence of a set of neurons in the adult human brain that respond selectively to music. It remains to be seen whether these neurons are present from birth,” Professor McDermott said. “It is possible that they emerge over development in response to the massive exposure most of us have to music throughout our lives.

“One way to address this would be to test whether comparable responses are present in the brains of young children, but we have not done this yet.”

It is also not yet clear whether these music-specific brain cells can explain differences in musical ability, which appears to involve both genes and upbringing.

“None of the participants in our experiment were trained musicians, and we didn’t evaluate their musical ability,” Professor McDermott explained. “One obvious next step is to repeat the experiment on musicians to see if their neuronal music selectivity differs in any way from that in non-musicians.”

Until now, many neuroscientists believed musical appreciation was simply a spin-off from the auditory mechanism in the brain that has evolved to understand speech or other complex sounds.

“One of the core debates surrounding music is to what extent it has dedicated mechanisms in the brain and to what extent it piggybacks off mechanisms that primarily serve other functions,” Professor McDermott said. “The fact that there appears to be a neural population that responds highly selectively to music is probably some indication of the importance of music to humans, but it doesn’t speak to music’s evolutionary origins – we don’t yet know whether the neuronal tuning is to any degree innate, and thus whether there is an evolutionary trajectory to investigate.

“That said, the existence of this neural response, and the method we developed to measure it, provides a tool that could in principle yield insights into the evolution of music. We can now probe for the existence of comparable responses in infants, to test whether music-selective responses are present from birth [and] in cultures that have widely divergent musical traditions – to test whether the brain’s analysis of music is strongly dependent on culture.”