Ever had a song stuck in your head for days? Now imagine not just thinking about it, but actually hearing it - clearly, on repeat, with no music playing around you. This is what people with musical hallucinations go through. The exact causes of musical hallucinations are still unclear, but there are plenty of theories about why our brains can suddenly decide to become a DJ.
Musical hallucinations (MHs) are a type of auditory hallucinations characterized by hearing melodies and tunes in the absence of an objective external stimulus. They usually involve songs that are personally significant to the person, such as favourite childhood songs, but can also be irrelevant or even disliked. Among other conditions, such as brain lesions or neurological disorders, MHs are most often associated with hearing loss.
The mental reconstruction hypothesis
The high prevalence of hearing loss in patients experiencing MHs has led to various hypotheses, of which the most common one argues that the lack of afferent stimuli to the auditory cortex feels unnatural to our brains. In response, they try to fill in this gap by internally generating sounds, such as jingles or tunes – just like you hum a song to feel better in an uncomfortable silence. This creation of music in the brain happens through uncontrolled spontaneous activity in the auditory network, modulated by various brain regions involved in emotional memory processing. This hypothesis is consistent with other cases of mental reconstruction, such as confabulations of missing memories, phantom limbs or Charles Bonnet Syndrome (visual hallucinations in visually impaired individuals, read more here).
Creation of sensory memories – simplified
To understand how a musical hallucination is formed, we need to start with how the brain encodes sensory experiences. When we experience a certain stimulus, such as a song, multiple brain networks are active at the same time. The auditory cortex processes the acoustic features, such as the melody and lyrics; the visual system might register the associated imagery, such as the environment in which the song was heard; the motor cortex might activate in response to rhythmic movements, such as you tapping your foot; and the limbic network evaluates how emotionally meaningful the moment is. Each of these networks gathers its piece of the experience and passes it along to the hippocampus, which forms it into a memory. The more frequently you hear the song and the more emotionally charged the experience is, the more likely it is that the memory will stick – ready to be recalled later.
How we spy on the brain
Our brains direct more energy (oxygen and glucose) into areas, structures and networks (groups of structures) that are actively engaged in the given moment. In neuroscience we can observe those areas using brain imaging techniques, such as magnetic resonance imaging (MRI) or positron emission tomography (PET), to observe which brain areas are given the most fuel during which cognitive processes. So, when we say that an area is ‘activated’ or has ‘increased metabolism’, it means that the levels of oxygen and glucose in those areas are significantly higher than in other places, because the brain is using them to perform a certain function.
Network imbalance in the silent brain
The neuroimaging studies of MHs have identified two competing networks that are involved in the generation of MHs: the extrinsic control network (ECN) and the default mode network (DMN). The ECN focuses on the external environment and controls which external stimuli reaching our brains come from the outside. The default mode network (DMN) is responsible for our internal perceptions, such as daydreaming and self-related thoughts. Interestingly, the DMN includes the cingulate cortex, which is involved in musical processing. In individuals with normal hearing, these two networks are usually in ‘competition’ and increased activation of one network leads to decreased activation in the other one. For instance, when we focus on an external stimulus, the ECN activation rises and DMN activation lowers. This inverse relationship between the networks allows to effectively distinguish between external and internal stimuli. However, in individuals with impaired hearing, the external auditory stimuli reaching the ECN are limited, significantly decreasing its activation. This lowered metabolism of the ECN leads to much less effective suppression of the DMN, which consequently leads to the inability to distinguish between outside and inside stimuli.
Your brain, the DJ
Our internal perceptions are usually guided by our memories, such as an emotionally significant song. As we mentioned before, those memories are stored in the hippocampus, which passes them on to the orbitofrontal cortex (OFC). The OFC evaluates the memory and assigns an emotional value to it, potentially leading to a vivid reconstruction of the memory. Given the imbalance between the ECN and the DMN, the internally reproduced musical memory can be mistakenly perceived as an outside stimulus, leading to the activation of the auditory cortex and a compelling experience of hearing a song that is not actually playing: a musical hallucination.
So what does it all mean?
Musical hallucinations are not just signs of a failing system – they are an example of how the brain tries to create a coherent experience, even when one of its vital modalities drops out and the world goes silent. When external sensory input fails, the brain does not shut down – it turns inwards, draws on memories and reconstructs reality the best it can. Understanding how MHs arise shows us something profound: perception does not only come from the outside world. It is a blend of signals, predictions, emotions, and memories – constantly shaped by what the brain expects and what it misses.
So next time a tune sneaks into your head uninvited, don’t be annoyed – your brain might just be trying to cheer you up, spinning tracks to keep you company when the world goes quiet.
Author: Zuzanna Kotwicka
References:
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