Mindscapes is our new column on brain science with a difference: we meet people who live with the world’s most mysterious neurological conditions
Condition: Musical hallucination
“It’s like having my own internal iPod,” says Sylvia. While she goes about her daily life she hears music. It may sound to her as if a radio is playing, but it is entirely in her own head.
Sylvia calls the hallucinations a nuisance, but they can be turned off, which has allowed researchers to work out what might cause them. The discovery paves the way for new treatments and hints at the cause of more common hallucinations, such as those associated with schizophrenia.
Eleven years ago, Sylvia experienced sudden, acute hearing loss. About a year later, she began to hear the constant repetition of two notes. Gradually these built into musical phrases and, over time, into full melodies. “They sound like a cross between a wind instrument and a bell,” she says.
Sylvia is a musician with perfect pitch so she was able to write down these tunes and record their development. Sometimes they sound like familiar songs. Others resemble passages from classical tunes and some are novel, short melodies.
She discovered that playing real music suppressed her musical hallucinations. This enabled Timothy Griffiths at Newcastle University, UK, and his colleagues to study what was going on in her brain while switching her hallucinations on and off.
Passages from J. S. Bach worked as the “masker” to switch the hallucinations off. Sylvia rated the intensity of her hallucinations every 15 seconds throughout the study, which lasted about 45 minutes. At the time of the experiment, her musical hallucinations happened to consist of sequences from Gilbert and Sullivan’s musical HMS Pinafore. Immediately following the masker, her hallucinations were at their lowest, gradually increasing until the start of the next excerpt.
Meanwhile, the team used magnetoencephalography to scan Sylvia’s brainwaves. The technique records magnetic fields produced by electrical currents that oscillate throughout the brain.
Picking up patterns
At any one time, brainwaves oscillating at different frequencies and associated with different tasks sweep through the brain. Fast gamma oscillations are thought to be involved in consciousness. Beta oscillations are involved in active thinking.
Sylvia’s scans showed that her musical hallucinations seemed to be generated by a network of higher brain regions, including those that process melodies and sequences of tones, and areas involved in imagery and memory. Fast gamma oscillations and slower beta oscillations in these areas increased when the hallucinations were present compared with when they disappeared.
So what was going on? In most people, sound waves enter the ear and are transmitted to the brain’s primary auditory cortex. This processes sounds at their most basic level – picking out patterns and pitch, for example. From here, signals that represent this basic information about the sound get passed on to several higher brain regions that process more complex features, such as melody and rhythm.
The brain’s shortcut
But rather than pass every detail about every aspect of sound up through each region, the brain takes a shortcut. Higher centres predict what sound might come next and pass that guess back to lower regions, where it is compared to the actual input. Only if that prediction is wrong does a signal get passed to higher areas, which adjust subsequent predictions. Several successive loops get passed higher and higher until all aspects of sound are fully processed and we become aware of it as music, say, or speech.
“If you were to pass messages about every aspect of every sound up through each level it would be a very inefficient way to run a brain,” says Griffiths.
With Sylvia, incorrect predictions are not corrected and this leads to hallucination.
But not all people who have hearing problems get musical hallucinations. In Sylvia, there is probably some malfunctioning connectivity in the two higher regions that make them start talking to one another, says Sukhbinder Kumar, also at Newcastle. “If this happened in a healthy person they would be constrained by the information coming up, but in Sylvia this information isn’t reliable and they keep on talking to each other.”
This also explains why listening to music can stop her hallucinations. “When Sylvia is concentrating on Bach, something she is familiar with, the signal entering her brain is much more reliable and that constrains the aberrant conversation going on in the two higher areas – and they reconcile themselves to what is actually happening,” says Kumar.
“In this situation, music may be more likely to be hallucinated than other kinds of sounds, such as speech, due to the intrinsic regularity of music and its repetitive, relatively predictable structure,” says Jason Warren, a neurologist at University College London. “This study illustrates how carefully designed experiments can, with the appropriate tools, capture even such apparently intangible and private experiences as hallucinations.”
“They might not arise from the same brain areas, but these observations are of importance in efforts to understand hallucinations that commonly occur in psychiatric disorders such as schizophrenia,” says Matcheri Keshavan, a psychiatrist at Harvard Medical School.
“It might be possible to disrupt the abnormal loops with brain stimulation,” says Griffiths. Or use pharmacological treatments to disrupt chemical transmitters that drive relevant oscillations. “Better hearing aids also appear to have an effect, which supports our model,” he says.
Sylvia looks forward to new treatments, and is pleased that her “nuisance” might help others. “I never experience quiet,” she says. “Sometimes a tune will play itself 1000 times in my head and become really annoying. I have learned to live with it but I can see how one could be driven mad.”
Journal reference: Cortex, DOI: 10.1016/j.cortex.2013.12.002
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