Before I left for Switzerland at the start of this month I printed off a few articles that I had hoped to read for background research, and also to provide you, dear reader, with some of the latest findings in music psychology.
Well, this hope has been slightly delayed. It has been a long few weeks here in Luzern as I have been balancing immigration admin, with the freedom that comes with being able to write up articles that have been sitting on my desk for months. I love being able to finally sit down to write up these interesting research projects. I have also been enjoying the planning and teaching of my new Music Psychology course, here at the Hochschule Luzern – Musik.
All this is why it has taken me a little while to get to my exciting pile of new papers. Here I am finally though, reading the first one.
This new paper tackles the question of whether musical hallucinations and tinnitus are similar phenomena. This is of interest to me as these two kinds of ‘auditory phantom’ may also be on a continuum with earworms, tunes that get stuck in our head (a keen research interest for me).
What is tinnitus? Tinnitus is when a person hears a simple tone or buzzing noise that is not coming from the environment. The term comes from the Latin word tinnire meaning “to ring”. Many of us will have experienced temporary tinnitus, perhaps after visiting a concert or nightclub, or exposure to other loud and prolonged sounds.
What are musical hallucinations (MH)? MH are complex false sound perceptions meaning that a fully conscious person might report hearing whole songs or other musical arrangements, all of which have no external source. Musical hallucinations are more common in older adults, especially those who are suffering from a degree of hearing loss. MH can also arise from brain lesions at any point in the auditory pathway, from the lower centres (e.g. brainstem) right through to the auditory cortices.
What do these two things have in common? Both MH and tinnitus represent the perception of a sound stimulus in the absence of any physical stimulation from the environment – people are hearing things that are not ‘there’.
In both cases people can often not realize at first that these sounds are not ‘real’ – they may go searching for the source of the sound (a hidden radio or a buzzing piece of electrical hardware) eventually to realize that the sound is being generated internally rather than externally. Because people can eventually recognize the internal source of the sound MH and tinnitus are not, by themselves, a form of “psychosis”, which is defined as a loss of contact with reality.
The new paper I am reading hypothesised that MH and tinnitus might share a common source in the brain that differs only in its complexity, with tinnitus producing simple sound and MH producing complex music.
The model: The model the authors chose was ‘Thalamocortical dysrhythmia’ (TCD), a suitably complex term (go on, say it three times fast, I dare you!). TCD is a theory that suggests the neurons in the thalamus can start to behave in an odd way, either diminishing their excitation or increasing their inhibition. This haywire activity at the neural level, known as ‘deafferentation’, can trigger both positive and negative symptoms in neurological conditions.
How might TCD cause tinnitus and MH? According to the new paper, tinnitus may be caused by abnormal, spontaneous and constant gamma band activity as a consequence of a particular pattern of deafferentation in the thalamic nuclei. This can be combined with an increase in theta activity, and perhaps also a decrease in alpha activity. This combination of abnormal firing patterns is known as the “edge effect”
The difference that turns tinnitus into MH might be found in brain areas like Broca’s , regions of the brain that handles both language and music stimuli. Perhaps a low level “edge effect” combined with higher brain centre abnormal activity turn simple tinnitus into MH?
The test: The new study used EEG to compare resting state brain activity between healthy controls, and people with either tinnitus or MH. The hypothesis was that both simple (tinnitus) and complex (MH) auditory phantoms will share a common neural signature of increased gamma-theta activity in combination with decreased alpha activity, as in TCD. Furthermore, only MH should involve traces of abnormal activity in higher music and language areas
The authors compared 10 people in each group (control, tinnitus and MH). The two clinical groups had both had their symptoms for at least a year and had comparable hearing loss (not severe).
The results: People with MH or tinnitus both showed increased gamma-theta activity within their auditory cortex. This finding alone suggests that TCD might underlie both simple (tinnitus) and complex (MH) auditory phantoms.
Interestingly both groups also showed suppressed beta band activity in their visual cortices. The reason for this is not yet known, but it has been reported in previous studies.
There was also increased beta activity in areas such as the dorsal anterior cingulate cortex and anterior insula during both tinnitus and MH. This activity might be related to the brain ‘filling in’ missing auditory information and brining the phantom auditory percepts to awareness.
What is unique in MH? People with MH showed more alpha activity, which we can explain as the increased memory load of dealing with complex percept as opposed to a simple buzz or ring of tinnitus. People with MH also showed increased resting state activity in right inferior frontal regions, areas associated with retrieval of familiar musical imagery from memory, and areas associated with language and music processing.
Conclusions: The TCD model may prove to be a suitable explanation for both musical hallucinations and tinnitus, since both were seen in the new study to feature the relevant abnormal patterns of neural activity. The future will tell us if similar patterns are seen in prolific earworm sufferers.
Complex phantoms (MH) in addition are associated with additional patterns of abnormal neural activity in various bands across areas of the brain that are associated with memory and musical imagery, but also language processing.
Sven Vanneste, Jae-Jin Song, Dirk De Ridder (2013) Tinnitus and musical hallucinosis: The same but more. NeuroImage 05/2013; DOI:10.1016/j.neuroimage.2013.05.107. Find and request a copy of the paper here.