Music on the brain

Musical hallucinations may help us understand how the brain interprets music and other complex sounds.

We all know what it is like to have a tune 'on the brain' – be it 'Raindrops Keep Falling on my Head' or 'It's Raining Men'. Sharing one's life occasionally with Sacha Distel or Geri Halliwell may be mildly irksome, but some people, usually with acquired deafness, have to endure a constant musical accompaniment to their lives. Patients suffering musical hallucinations hear music or other sounds all day long, day after day – a distressing and debilitating condition.

"One of our patients hears 'Songs of Praise' all day," says Tim Griffiths, a Wellcome Trust Senior Research Fellow in Clinical Science investigating musical hallucinations at the University of Newcastle upon Tyne. "Others hear songs by Shirley Bassey or nursery rhymes – tunes they heard before they became deaf." Unfortunately, there is no treatment for such patients. But by studying musical hallucinations and other central hearing disorders, Dr Griffiths hopes to discover more about how the brain processes musical and other auditory stimuli.

When we hear music, speech or environmental noises, the brain has to decode the patterns in the sound before it can decide what the sound is. Complex sounds contain a number of elements that vary in frequency, time, loudness and position. In music, for example, melody reflects patterns of sound pitches, while rhythm involves variation in the onset times and duration of sounds. These patterns are processed in a series of brain regions between the cochlea and the high-level areas where the brain assigns a meaning to the sound or remembers where it was heard before. "If I say the word 'cat', it's a pattern of sound but at another level it triggers a picture of a cat in your mind," says Dr Griffiths. "Music and environmental sounds also have meanings associated with them, so we are working on the acoustic features of complex sounds that are important for us to process particular types of information."

Problems with sound processing can provide insights into the brain's normal mechanisms. "We're looking at people who have had strokes and other brain lesions, and testing their ability to detect sound patterns," says Dr Griffiths. "You can use that as a way of inferring what are necessary parts of the brain for those kinds of mechanisms." Patients come to the newly opened Clinical Laboratory for Complex Sound Perception at the University of Newcastle from the Newcastle Cognitive Neurology Clinic, run by Dr Griffiths, and from other clinics in Newcastle. At the laboratory, psychoacoustic tests (where subjects make responses to sound patterns) and EEG (brainwave) recordings in response to patterned sound are carried out.

Systematic batteries of hearing tests, developed by Dr Griffiths, look at patients' ability to process patterns of sounds. These sounds are more complex than the simple tones or clicks used to see if someone is deaf, in which the function of the cochlea in the ear is being assessed. "In one type of test you get people to listen to two sounds, one of which wobbles and one of which doesn't, and ask them whether they can detect change or not," he says. "We can change the level that the wobble goes up and down to find the threshold for detecting that sort of pattern."

In parallel with these studies, Dr Griffiths uses the same kinds of sounds in positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) experiments at the Wellcome Department for Cognitive Neurology in London. "We play the sounds to people and look at what parts of the brain are normally activated, in terms of bloodflow, when you process patterns in such sounds. These experiments are quite difficult to do – especially with functional MRI where the machines themselves are very noisy."

Using functional imaging, Dr Griffiths has found that patients with musical hallucinations have spontaneous activity in the parts of the brain that process patterns of sound. "This activity appears to spark memories of music," he says, "and a kind of positive feedback keeps the music playing over and over."

Both the sound-processing tests and the imaging studies can help us understand how the brain works, but Dr Griffiths is also interested in using disruptions in sound processing as a window into a range of neurodegenerative disorders. "As we examine more complex types of sound, we're looking at increasingly more distributed areas of the brain that are involved," says Dr Griffiths. "A number of neurodegenerative disorders, such as Alzheimer's disease and frontotemporal dementia, involve distributed wear of the brain, including those that we have identified for complex-sound processing. This might be a way of picking up deficits such as Alzheimer's disease at an early stage, and would be a clinical application that goes beyond the basic-science questions that we've addressed to date."

Music on the brain

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