Dopamine Signaling'S Role In Music Therapy'S Neuroplasticity

Theoretical Summary

Music, evidently roots back to approximately 42.000 years ago. (Barras, 2014) Some suggest even earlier dates, where it was most likely used as a survival mechanism for further emotional engagement between infants and caregivers. Although, as the child gains capability throughout their upbringing, a higher-level communication -such as language- is preferred as a more effective and precise way of conveying emotions. It seems plausible that music could stay limited to that function, but it maintains its value as it also poses a way to release emotions, without the need of acting on them. (Schmidt & Trainor, 2003) Ancient Greeks viewed music as either a purification of the internal soul (catharsis) or a representation of the external world (mimesis). (Juslin, 2005)

Currently, it is known that music provokes emotions in us both by learned contextual associations, and by musical expectations acquired from statistical properties of musical structures. (Egermann, Emotional responses to music) The integration of both ancient and modern views of music shaped the present level and manner of usage of it in our daily lives, often surpassing the scope of our awareness. Music changes how we perceive reality, (Murphy, 2012) an essential ability to match our surroundings. Correspondingly, music has shown to affect processing of visual emotions, e.g. a neutral face appears happy to individuals listening to music inducing positive emotions, and the same goes for negative emotions as well. (Tiziana Quarto, Giuseppe Blasi, Karen Johanne Pallesen, Alessandro Bertolino, & Elvira Brattico, 2014) Perception is the subjective interpretation of objective reality that requires neuropsychological processes to encode, break down and then reintegrate incoming information. (Vervaeke, 2018) Accordingly, music interacts with diverse regions of the brain, including non-musical areas, rather than being limited to an area. (Marie Forgeard, Ellen Winner, Andrea Norton, & Gottfried Schlaug, 2008)

The scope of music’s effect has been salient, since the emergence of beliefs suggesting that diseases could be healed by harmony and balance. (Gryglewski, 2015)

This concept emerged again from a clinical sense for calming veterans of World War I & II, suffering from PTSD. (Bronson, Vaudreuil, & Bradt, 2018)

The positive effects were observed directly from the physiological responses e.g. heart and respiration rate, skin conductance, etc. Also, repeated demonstrations following music therapy detected (Richards, Johnson, Sparks, & Emerson, 2007) reductions in perceived pain and anxiety in patients, suffering both from psychological and physical disorders, through a cascade of subconscious activity; which resulted in increased usage of music for therapeutic purposes. Music cognition studies provide some insight regarding the processing of musical stimuli in the brain, where the prominent contributing mechanisms are the dopaminergic pathway and neuroplasticity. However, the exact processes are still at issue. This essay explores the extent of dopaminergic system’s role in the machinery to benefits of music therapy.

Evidence Integration

Even though the experience music prompts us with differs by the myriad of individual and musical variables, fMRI studies (Chen, Penhune, & Zatorre, 2008) have shown that all individuals share the main regions of brain when processing music: areas targeting movement, motor planning, attention, and auditory cortex. The neural circuit loop formed between auditory and motor system allows sound perception and production (Zatorre, 2015). In addition, a key concept in music cognition is that brain finds emotional meaning in music and causes the release of dopamine in several regions of brain, at both the peak emotional level and at the anticipation of the moment. (Zatorre, 2015) This neurotransmitter simply operates for reward and motivation, essentials for healthy functioning of an individual as it poses a survival value. (Klein et al., 2019) Both animal and human studies have revealed that increase in dopamine generated species-specific seeking and approach-related behavior for rewarding stimulus including food, copulation and aggression. (Chan, 2019) Meanwhile, lesions to dopaminergic regions of monkey brains, specifically Nucleus Accumbens, have demonstrated a marked decrease in motivation. (Chan, 2019)

Dopamine pathways are structured deep inside the brain; supportive of the evidence from phylogenetic studies suggesting it is ancient machinery. This also gives an account as to why we can feel such powerful emotions with music. Music has a uniform rhythmic nature, which makes the ability to perceive temporal regularity an essential, in coordinating movements cued by it. Neurological studies, examining correlates of beat perception have shown that listening to isochronous rhythmic sequence induces activation in regions aiding the creation of anticipation of the next sound. Besides the dopamine release in the case of a rewarding event, this also suggests that perceptual regions for planning, i.e prefrontal cortex (PFC), are involved in music processing. Neurologic research from patients with disorders of consciousness has proved that even when the patients are unconscious, the anticipatory effect still stimulates the dopamine system. The essential verdict is that neither awareness nor attention is required to get the benefits of music. (The effect of anticipation will be further explained later on.)

Sound Processing

This music perception differs from brain’s treatments to sounds that are not music and are unpredictable. When sound first enters the brain, cerebellum processes the incoming sound wave in a primitive low-level fashion by its simple physical attributes to relay it onto thalamus, the executive center of brain that makes sense of the processed information and decides as to what to do. Thalamus then communicates both with hippocampus, region responsible of memory storage, and amygdala, responsible for negative emotions, to decide the following reaction based on whether there’s any semantic associations. Brain categorizes sound into music by the interaction of low and high level processes.

Although, if the sound does not pose any semantic information by itself, this does not occur. If the sound is not uniform, it would not generate anticipation nor a dopamine response. Studies of stroke patients with unilateral neglect have shown that their visual attention improved best with classical music compared white noise, while both of the outcomes were superior to that of silence. Other findings have also demonstrated that just background noise can in fact, impair cognitive abilities. For instance, it appears that speech is more similar to random noise, regardless of the phonetics of language, and is harmonically more dissonant than songs. Further research states that cognitive dissonance, the mental discomfort emerging from conflicting cognitions, can be alleviated by consonant music, while facilitated by dissonant ones. This implies that consonant harmony has the tendency to trigger more dopamine response. Further meta-analysis of music used in successful therapies, and comparing dopamine levels with both, could clarify the importance of the neurotransmitter. Although, these findings imply the success of music therapy is not a result of hearing sound, but due to the induced dopaminergic pathways in brain upon differing qualities of music.

Musical Depth/Complexity

Music can also be categorized by depth, arousal and valence. While the definition of depth seems rather unclear, it is mostly correlated with intellect and sophistication of music that is complex, such as classical, avant-garde, world beat and jazz genres. A growing body of research found a positive correlation between intelligence and classical music. Intelligent people tend to choose to listen to complex music, while neurobiological evidence supports the opposite as well: (2004) Examining brain activity of rats after listening to Mozart, found an ‘increased gene expression of BDNF, a neural growth factor, CREB, a learning and memory compound, and synapsin I, a synaptic growth protein.” Many similar studies have revealed that classical music induces a great amount of neuroplasticity. This effect has drawn a significant amount of attention named as ‘the Mozart effect’, and is the rationale for the high recommendation among various contexts.

Evidently, the association between intelligence and musical depth is through working memory (WM). WM has a limited capacity*, which can be increased by chunking and reorganizing. Music is structured; hence, it allows efficient chunking. This displays as meaningful emotional engagement with music. Listening to complex music trains our ability to make sense of information that is harder to chunk and process, emerging as enhanced memory and attentional abilities that serves well to intelligent problem solving. Mammalian studies report complex information boost brain’s production and survival of neurons in hippocampus, which brings additional clarification to the Mozart effect as well.

There is no clear link between complexity and dopamine release, which suggest that he essence of music therapy may not lie in dopaminergic system, but in neuroplasticity instead. However, a 30-minute session of a standardized Neurologic Music Therapy (NMT), has displayed improvements in executive functioning tasks and mood, while not being able to replicate the past improvements in attention or memory. The key finding that memory enhancement consistently seems to follow mood results, still entails the significant role of dopamine signaling in the observed behavioral enhancements following music therapy.

Memory

Dorsolateral part of PFC (DLPFC), the distinguishing part of human brain from primates allowing high-level processing, plays an integral part in cognitive flexibility. This is an essential function of WM and to central executive in particular, which monitors and controls alternative courses of action to adapt changing goals. A study has investigated neural correlates of WM by a delayed match-to-sample task, where the subject was required to remember the presented sample to match the comparison stimuli during the delay. DLPFC was fired during the delay period, leading to the conclusion that the area is responsible for reactivating and reorganizing information to increase associative abilities. This is an important function, as we made the inference that dopamine release relies on the emotional semantic value an item holds. Salimpoor (2013) have demonstrated that as the assigned value to music increases, dopaminergic system correspondingly strengthens its communication with the auditory cortex, making the perceptual regions more strongly coupled with emotion and reward systems. Additionally, assigning value also depends on past experiences and hence memory mechanism. Concordantly, NMT and group psychotherapies have proved to manifest into increased cognitive flexibility, along with the enhancements in measures of visual attention, verbal learning, complex verbal memory, complex visual memory and planning – all of which supported by neural correlates. It seems that memory is the core function that aids in dopamine release that neuroplasticity depends on. As memory exhibits an integral role, it is worth mentioning its tremendous reciprocity with learning.

Learning

As mentioned above, temporal perception creates anticipation, and hence dopamine release. The forming of anticipation requires acquisition/encoding of patterns, which depends on memory. The firing pattern of dopaminergic neurons in VTA (mesolimbic subsystem of dopamine) exactly mirrors reward prediction errors (PE), the mismatch between prior expectations and reality. This is the same mechanism that also accounts for reinforcement learning in artificial intelligence, the ever-improving accumulation of algorithms for targeting an event by getting feedback from environment about how right/wrong the own predictions were. Minimizing the error between predicted and actual value of target items aid in learning surprisingly complicate sequences, which is analogous to humans.

This finding, once again, proposes that memory is, in fact, the essence of music therapy and not dopamine. Dopamine does not create, but acts on the PE from the acquired pattern and feedback, which makes it deeply coupled with learning, both anatomically and functionally. In this case, dopamine has the following essential role to act on PE from the acquired pattern, to signal for neuroplasticity from the emotional associations. Dopamine is anatomically and functionally profoundly coupled with learning, it makes sense of acquired pattern and the feedback and induces structural changes in brain.

Neuroplasticity

Dopaminergic system uses this information to modulate synapse-specific, excitability-enhancing neuroplasticity in several cortical networks including the sensory cortex (Bao et al., 2001; Hui et al., 2009 The changes correlate in structural connectivity and behavioural measures, leading to the distinguishable effects of music therapy on patients with psychological and physical disorders. Examples include thickening of auditory, motor and frontal cortices with music training; all of which are used for sound perception and production as well as planning. Another brain imaging study showed enhanced verbal material encoding with background music, compared to silence, suggesting music serves as contextual cue for item recognition. Additionally, the improvement reflected as reduced DLPFC activation in brain. As music improves semantic associations, the cognitive demand put on the frontal cortex has decreased with music training. The encoding ability became more automatized, reflecting a greater neuronal efficiency. Accordingly, similar findings manifested from dopamine stimulation studies, demonstrating an improved cortical signal-to-noise ratio (SNR), a measure of salience comparing levels of desired signal with that of background noise.

An enigma of neuroscience is how abstract concepts like perception and consciousness emerge from physical materials. For this case, Graph theory proposes that they do not arise from specific brain regions, but from connectivity instead. This fits well with the ideas of both changing neural connectivity and perception with music. Studies have shown that music rehabilitation lead to enhanced autobiographical memory. Analysis of the underlying mechanism has revealed that the key factor was the reduced perceived anxiety with music, serving as an example of perception change. Similarly, increased chronic stress produces imbalances between white and grey matter, making one more vulnerable to further mental illnesses. Once more, this puts forth the importance of emotions as the underlying mechanism of music therapy. The changes in functional connectivity require axonal pathway changes and progressive growth of nerve terminals, which is exactly how synaptic neuroplasticity occurs as both animal and human studies have presented. The changes seem to be much more effective with younger age, since the maturity of pathways are not as consolidated as adult brains, allowing room for bigger changes.

Conclusion

Music represents a mechanism by which humans have learned to enhance emotional arousal and regulation by interaction of ancient reward systems with more phylogenetically advanced perceptual mechanisms, the distinctive region of our brain from any other animal.

Music therapy has served a range of diseases, where the dopaminergic system responsible for reward and motivation plays a central role. A key factor stimulating its release is music’s characteristic of temporal regularity and a semantic value attached. The qualities of music also have an influence; consonant harmony and complex music are correlated with increased change in neuroplasticity, reflecting in behavioral measures. The association is deeply interconnected with WM processes, especially chunking and executive functioning as supported from structural changes in brain. WM seems to be the initial mechanism for attaching semantic value and creating anticipation using patterns from experience, which reflect to dopaminergic neurons firing by implicit prediction errors to cause neuroplasticity.

In this way, music proves to be an effective rehabilitation approach with the ancient and inherent mechanisms it holds, available at any time without side effects. Dopaminergic system seems to have an important value in account of the change and neuroplasticity. Although, memory processes are the opening gambit making such enhancements possible. The fact that there are many variants in the equation that could lead alterations in how much one benefits from music therapy.

Further research clarifying the connection could encourage emergence of more optimized NMTs, as well as aid in broadening our understanding of brain. Additional suggestions: Would the effects habituation following repeated music treatment?

Could critical period be mimicked to induce higher and faster changes in quality of life, following music treatment?

Could preceding memory training increase the extent of music therapy?

Bibliography

1. Vervaeke, J. (2018). Cognitive Psychology: WM & Theoretical Debate [Powerpoint slides].
2. Zatorre, Robert. (2018, April 12). How Music Changes the Brain [Video file]. Retrieved from https://www.youtube.com/watch?v=KVX8j5s53Os
3. Chan, V. (2019). Cognitive Neuroscience: Emotions [Powerpoint slides].