I’ve just removed this from my new book because it didn’t fit. Seems a shame not to use it somewhere, hence the post.

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Musical hallucinations are a case in point. These are auditory hallucinations in which a piece of music is heard over and over again in someone’s head. The music is usually familiar, although the condition generally affects older people and the music can date from many years ago. Most interesting to me though is the fact that these hallucinations can occur if the physical senses – or sensory inputs to the brain – have too little external stimulation. So whilst going to a thinking cabin in the woods for a week might be a very good thing, indulging in deep silence or stillness for too long may eventually result in you hearing things. Why does this happen?

According to experts such as Jerzy Konorski, a neurobiologist writing in the late 1960s, it is because sensory connections are a two way street. We have pathways between our eyes, ears, nose, skin and so on to our brain but these pathways also work in reverse, so that the brain can pick a memory of an event (the hearing of a piece of music, the smell of a freshly baked cake or the feeling of a leg long since lost) and ‘play’ these experiences back to our physical sense receptors. These nostalgic connections are not as strong as the ones going the other way but they do exist and they can come to the fore, especially when sensory input from the eyes, ears and so on coming the other way is weak or non-existent. In other words, a strong flow of sensory inputs to the cortex prevents this backwash from occurring.

As you’d expect the science has moved on somewhat from the late 1960s and in 2000 Timothy Griffiths produced a paper that showed the effect is indeed real. Using PET scans Griffiths showed conclusively that musical hallucinations were real and also that the neural networks that are activated when a patient has a musical hallucination are virtually identical to those that ‘lit up’ whilst listening to ‘real’ music. As far as the brain is concerned there is almost no difference between the two.