A brain basis for musical hallucinations 7


 

lucerne

Hello Dear Reader,

I hope your January is going well. We are experiencing an unusually mild winter here in Switzerland so far. Very little snow has reached Luzern, which stands 400m above sea level. But at least I can now see snow on the mountains (including the stunning Mount Pilatus) from my office window, and very lovely it looks too.

Today I have been reading a new article (in press) in Cortex which claims to have identified a brain basis or at least a brain based explanation for musical hallucinations (MH). My interest was peaked – perhaps this might give a first clue about a brain basis for earworms?

Earworms (tunes that get stuck in your head) and MHs (complex musical perceptions with no external source) are not the same thing though they have a number of common features, both being musical and related to mental imagery.

The main difference as far as I am aware is one of conscious inference regarding the likely source of the sound: One is clearly recognizable as a memory (earworm) whereas one could easily be mistaken for the experience of real music listening (an hallucination).

A few weeks ago I write a blog about the difference between MHs and tinnitus. This blog was based on a new paper (Vanneste et al., 2013) that compared the resting brain state activity (using EEG) of people who experienced regular tinnitus (a sensation of ringing in the ears) or MH to that of spontaneous activity.

Neuron_in_tissue_cultureThe result of this paper was a theory that abnormal firing of neurons in some bandwidths (alpha, gamma-theta) in the lower centres of the brain was associated with tinnitus.

By contrast, MHs were associated with abnormal neuronal firings in the higher centres of the brain, those associated with memory and language processing.

 

This idea of ‘hierarchical levels’ of abnormal neuronal patterns in the musical brain pathway was a nice intuitively sensible conclusion. It was also interesting to see some brain basis for these conditions as opposed to the more common idea of blaming everything on the inner ear.

The new paper by Sukhbinder Kumar and colleagues takes a case study approach instead. The team looked at the experiences and brain activity of one 62 year old keen amateur musician who had absolute pitch. This lady had experienced MH 15 months after the onset of acute hearing loss, approximately a year and a half before she took part in the study.

When she first started experiencing MH the lady assumed that the sounds came from an external source – by my definition that qualifies them as an hallucination rather than earworms, even though she now knows that these musical sounds are not real (they appear to always be the same few bars of recognizable melodies).

NIMH_MEGThe authors used a clever technique to assess her MHs as they happened in an MEG scanner.

Her MHs could be suppressed by playing short excerpts of music by Bach (like a mask) so the authors compared her brain activity across time in a single scanning session as she moved in and out of a state where she experienced MHs.

 

A beamforming analysis was then performed on the brain data to isolate patterns in oscillatory activity during MH across five frequency bands: 1-4Hz (delta), 5-14Hz (theta/alpha), 14-30Hz (beta), 30-60Hz (gamma) and 70-140Hz (high gamma)

Results: Significant power changes during high periods of MH were observed in the theta/alpha, beta and gamma bands but not in delta or high gamma.

None of these changes were localised to the right hemisphere and all changes referred to increases (rather than decreases) in oscillatory power.

Area 1 of activity was the orbitofrontal cortex (theta/alpha activity). This area has been associated with responses to unpleasant music and imagery. It is perhaps not surprising to see this activity therefore, since the lady was often bothered by her MH. 

Area 2 of activity was the motor cortex (beta activity) which the authors link to the well established activation of motor areas in response to musical imagery, particularly in musicians.

Area 1 of activity was the secondary auditory cortex (aSTG – gamma activity). This area is involved in melody perception.

Traffic_light_greenHow do these results compare to the previous paper? This paper and that of Vanneste et al. (2013) show an increase in gamma in relatively ‘lower’ brain areas (secondary sensory cortices – green) and an increase in alpha and beta power in ‘higher’ brain centres during MH (motor cortex – orange ), which fits with a hierarchical theory of MH.  The present paper takes this hierarchy idea to propose a new model for the brain basis of MH. Their theory presupposes only the presence of hearing loss.

Crucial to this model is the existence of a top down predictor system that we build through a lifetime of musical listening. This system of ‘priors’ sends predictions back through the musical perception pathway in response to sensory stimulation in the level below. Ascending (upward going) information about the music being heard then consists only of any information on prediction error so that higher level expectations can be modified.

It is a Bayesian optimised prediction system for music.

Top down musical prediction from priors – bottom up prediction errors

When someone loses their hearing the brain responds by lowering the sensory precision of the lower sensory centres of the brain (in this case the auditory cortex). That leaves the next level of the hierarchy increasingly sending through prediction error messages to the higher systems, unchecked. And the higher centres reciprocate with backward prediction messages, creating a loop that leaves out the lower level.

In theory this leaves a cycle of communication between the brain areas that drive basic melody perception and imagery (and memory) without the strong input of the lower sensory systems to feedback a prediction error based on what is actually being heard. This leads to a MH.

musicWhy music? As compared to speech or images, music is more predictable and repetitive. It is also rapid and temporal meaning there is more pressure to alleviate strain on the sensory systems, to support them with predictions from higher centres. These combined characteristics mean music is more subject to the activity of priors; music’s own recursive cyclic characteristic is what lends it to be the basis for hallucinations

…and perhaps is why earworms tend to be musical too.

What does this tell us about earworms, and what is missing? If we accept the hierarchical prediction model of the musical pathway then we might presume that any spontaneous activation of the system (for example, in memory) might trigger reciprocal communication within part of this loop. A tune therefore might get stuck in our mind when we have an earworm in the same manner as a MH.

What we don’t know is: a) how this activity is triggered in the first place in either MH or earworms; b) why the loop goes on and on; and c) what part of the model makes the difference between a MH and an earworm

It might explain however, why listening to music often helps people deal with earworms (as you can read about in my upcoming PLOS ONE paper on earworm cures!), as the ascending musical input of prediction errors in this case would break the cycle of internal musical imagery.  

What does it NOT tell us about MH? This paper provides an explanation for MH as a result of hearing loss – it does not provide an explanation for MH that are experienced by people with a psychosis or as a result of a focal brain lesion. Why do people experience MH when there is, on the face of it, nothing wrong with the lower hierarchy (the sensory systems)?

Conclusions

This is a really nice paper that stimulated great conversation in my office about the nature of perception and mental imagery, both in the musical world and beyond!

I think these Bayesian network ideas are here to stay so I advise you to have a go at reading this paper and to think about how the brain’s way of dealing with rapid, temporal sensory input (i.e. relying on top-down predictions) might influence what we experience as part of consciousness.

Article: Kumar, S., et al., A brain basis for musical hallucinations, Cortex (2014)


7 thoughts on “A brain basis for musical hallucinations

  • Renan Carloto

    Hello Vicky, congratulations for the work, I’m from Brazil, I’m 25 years old, student of Design, and I have followed your blog.
    I’ve been having anxiety attacks since July, due to the earworm started to bother me dpois a mild trauma because I think having OCD moments before sleep, wondering not get away from thinking about a nickname I do not like being called thus using the musical thought to flee, days after realizing that the songs not stopped over in my head.
    In these six months, I’ve been trying to find ways to avoid anxiety, and cut a little musical thought, I wonder if you could recommend something, so that I can better accept this. I think I have feedback that could help in their research. Would you like to help and be helped as well.
    If you know some more Brazilian with the same symptoms, let me know. it is strange to be the one.
    Thank you.
    up soon.

  • vicky Post author

    Dear Renan. Thank you for your message and for following my blog. As in all cases of errant musical experiences, if you are experiencing anxiety or stress then my recommendation is to seek medical advice. I am not a medical doctor so I can’t ethically advise you on matters of your health. It sounds like your experiences, musical and otherwise, would benefit from tackling the root cause of your anxiety – my research has shown that earworms can occur for some people in heightened moments of stress and those same people report that when they manage to relax the music does not bother them as much. My hope would be that tackling issues of general anxiety will have benefits for you in many ways. I wish you all the best, Vicky

  • Renan Carloto

    thanks for the tips, Vicky.
    I will seek a specialist, had already realized that I dealt better being more relaxed. Another thing that helps a lot in the disappearance of earworm in my experiences, is be drawing.
    Well, continue reading, and enjoying watching your progress.

    Again, congratulations for the work

  • Dorothy Easterly

    I am struggling with musical hallucinations. My problem began during early December, 2014. Since they began I have had non-stop music in my ears. I have found that I can sometimes consciously change the tune, but it will change on its own. The music is there 24/7. I am a 72-year-old woman with profound hearing loss in both ears, and I have worn hearing aids for approximately 15 years. The hallucinations occurred around the time that I had a vertigo attack that left me with additional hearing loss. Sometimes I think I will surely lose my mind!

  • vicky Post author

    Hello Dorothy. Thank you for contributing your experience to the blog. I know it is not a big comfort but I can assure you that you are not alone and that there are other people out there, especially women who are experiencing hearing loss, who have to cope with musical hallucinations every day. Hearing their stories makes me wish there was more recognition of the conditions and more support available. IN fact, I am thinking of setting up an online community – I wonder if that would be useful? Anyway in the meantime Action for Hearing Loss have produced a nice fact sheet which contains some useful information. If you have not already found it then you can access it here: file:///C:/Users/Vicky%20Williamson/Downloads/Musical%20Hallucinations_Pulsatile_tinnitus.pdf I wish you all the best, Vicky

  • Deborah

    Has any one had a break down or committed suicide due to this ? I am not sure how much longer I can avoid either.

  • vicky Post author

    Dear Deborah. I am very sorry to hear that this condition is making your life so difficult. I implore you to seek professional medical help as soon as possible. Musical hallucinations can often play a part in triggering depression or anxiety, and in that case an individual needs to seek treatment for the symptoms that are upsetting their life. Please do not suffer alone. Mental pressures are not a weakness or your fault, and help is out there. If you do not like or trust doctors then I suggest you contact a counselling service directly. The NHS or Samaritans or organisations like ‘Action on Hearing Loss’ (who have some good factsheets on tinnitus and hallucinations) can offer options in your area. You have my deepest sympathies. I sincerely hope you find a way to improve how you live with this condition.

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