When I was a boy, music was like a friend to me. I would make up sounds on the piano by pushing down several notes at a time, over and over again, listening to the different shades of colour as I shifted notes, learning to hear how they blended together or clashed. The sounds helped me work through my feelings, whether joyful, curious, anxious or complicated. As my interest in music finally evolved into a research career, I’ve come to understand that the ideas and sensations contained within music are densely packed, capturing complex feelings that we acquire from whole life periods, acting like a magic coin with all of our memories emanating from one side and our future possibilities emerging from the other.

For the past 30 years I have been trying to understand the mysteries hidden within music and the great power it can have, not only for hearing-abled listeners, but also hearing-impaired people who experience music in their own way. When I began this journey, I never imagined the range of benefits music can have. It can help people with dementia rediscover lost memories and a sense of identity. It can help others with damage to language areas of the brain following a stroke to speak again. It can lead people with Parkinson’s disease and severe movement impairment to move freely, even to dance. It can help people with autism spectrum disorder to express their feelings, nurture relationships and improve social skills. And all around the world, music brings us together, shapes our beliefs and desires, and gives us hope and a sense of purpose.

How is this possible? If music is “medicine for the soul”, what are the active ingredients that make it so special? Which areas of the brain are activated by music, and why is this neural activity beneficial for us? Is music restricted to sound, or do we engage with music using all our senses?

The simple answer is that music concentrates a number of psychological functions into a convenient and highly efficient package, like the concentrated orange juice my mother used to buy from the local grocery store. But instead of juice, music concentrates psychological functions such as emotion, attention, timing, a sense of self and feelings of social connection. By engaging with music, the outcomes of processes that would normally take considerable time and effort can be achieved with remarkable efficiency. In other contexts of life, those same functions are present, but they are diluted by irrelevant circumstantial detail and long stretches of time. Music concentrates functions into small, densely-packaged moments.

One of the most powerful capacities of music is its connection to our sense of self and the personal experiences that make us who we are. Like Proust’s petites madeleines, music condenses feelings and memories that arise from whole periods of life. Such feelings go beyond simple dichotomies like joy and sadness, which are so often measured and analysed in psychological studies of music. Instead, music can bring to mind and coalesce an understanding of one’s emotional life in general. At first, memories evoked by music may seem nebulous and transient. But it is possible to explore them.

My own parents enjoyed playing Chopin Waltzes on the piano after dinner when I was boy. This has since prompted me to learn some of those same pieces myself. Not only are they beautiful and emotional; they also are steeped with personal significance. Sometimes while playing them, almost forgotten childhood images flash before me: a bedroom, the street where we lived, the backseat of a car, a friend. Deep inside the music, whole periods of my life are enshrined: growing up in Connecticut, and the momentous journey to our new home in Ontario, Canada. Such music-evoked autobiographical memories, or MEAMs, have been the topic of considerable research. Seminal work by Petr Janata shows that when familiar songs from our past trigger personal memories, brain activation is found in dorsal regions of the medial prefrontal cortex (MPFC) – an area of the brain that supports a sense of self. In some cases, MEAMs are richly detailed.

When I engage with music, the feelings and memories evoked are sometimes as vivid as lived experience, miraculously compressed into thin slices of meaning. Music evokes not only the narrative aspects of experience, but bodily sensations too, affecting physiological functions such as breathing, heart rate and skin conductance, and widespread neural activity in brain regions such as the amygdala, hypothalamus, hippocampal formation, right ventral striatum, insula, pre-supplementary motor area and orbitofrontal cortex. The result is that we feel memories and emotions in our minds and bodies, and these embodied sensations transport us back in time. This capacity of music – to condense complex emotions and memories into embodied thoughts and feelings – is one of the most powerful ingredients of music, and is often employed for both pleasure and for therapeutic ends.

The field of music therapy was developed in the 1950s and has expanded as researchers uncover the enormous potential of music to address psychological challenges. The broad goal of music therapy is to optimise quality of life and improve physical, social, communicative, emotional, intellectual and spiritual health and well-being. But research suggests that music can also be used to treat serious neurological conditions such as Parkinson’s disease and dementia.

Parkinson’s disease is a movement disorder, and its symptoms include tremor, rigidity and bradykinesia (slow movement). Neurologically, it is characterised by the presence of Lewy bodies (abnormal deposits of protein within nerve cells) and a reduction of dopamine, a neurotransmitter important for motor and other functions. However, some of the symptoms of Parkinson’s disease can be alleviated using a therapy called rhythmic auditory stimulation, or RIT. Severe problems of mobility are common in Parkinson’s disease, but people with such movement disorders often walk freely while they listen to music, especially if that music is strongly rhythmic and familiar. Rhythm promotes fluid movement because muscle contractions and extensions can be coordinated in time with other muscles, helping to organise a person’s movement like a dance.

In the case of dementia, people often struggle to maintain their sense of identity. Dementia is an umbrella term for a group of neurological conditions that result in the death of brain cells and cognitive decline, with Alzheimer’s dementia a common and well known form. As memories of past experiences and family members start to fade, so too does their sense of self or identity. Yet music can bring them back to themselves, triggering personal memories and enhancing social connections, in some cases beyond the listening experience.

Several years ago, my colleague Amee Baird and I were contacted by a senior who was caring for his spouse of 57 years. At the time David got in touch with us, Barbara was 77 and had been living with Alzheimer’s dementia for five years. As her condition worsened, she would get lost, misplace objects and repeat herself. She was also becoming increasingly agitated and confused, and sometimes did not even recognise David. Eventually, she began to accuse David of being an intruder, and chased him out of their family home. Barbara was suffering from a condition known as Capgras delusion: the belief that your partner is an imposter.

Misidentification delusions are rare, but can sometimes occur as a comorbid symptom in dementia. In Barbara’s case, the episodes occurred intermittently and from out of the blue. One minute, she would seem to recognise David, but if she went out of the room for a moment, upon her return she might look at him with surprise and demand: “Who are you?” Such episodes usually lasted one to three hours, so David would often sit in his car and wait it out, not wanting to frighten Barbara by remaining in the house. But Barbara noticed his tactic, and when chasing him out of the house would shout: “And don’t sit in the car! that’s David’s car”.

David was devastated: he didn’t know how he could make Barbara understand that he was her partner of nearly 60 years. He worried she would forget all of their shared experiences, including how much they had loved dancing with one another over the years. On the night they first met, they had danced to the last song of the evening, Unchained Melody. Since that night, the song had become a theme song for them as a couple, with all the rich memories of a shared life together embedded in this music.

On the recommendation of his family doctor, David began singing this song to her every day, lingering on the lyrics, “I’ll be coming home, wait for me.” And it worked. In his words, “She came back”, and the alienating episodes of her failing to recognise him stopped. The music had evoked memories of their full and rich life together, and the embodied feelings of that first night when they danced together. So now, almost 60 years later, they danced together again as he sang, despite the severity and steady progression of her dementia. As her verbal capacity had deteriorated, few words were spoken, but when they danced he felt connected to her all over again, remembering the moments of the life that they shared.

Music is powerful because it compresses several psychological functions and autobiographical memories into a package that is highly enjoyable and universally accessible to all. It is simultaneously physical, emotional, engaging, social and deeply personal. And so, combining these psychological functions makes it highly effective as a non-pharmaceutical intervention. For the most part, music-based treatments have few negative side effects, especially when used by a qualified music therapist. As evidence accumulates about the unexpected benefits of music, new treatments are being refined in order to emphasise the active ingredients that best match the needs of patients, whether they concern mobility, emotional connection, cognitive function, social engagement or a sense of self. Musical moments can be momentous, and I hope never to lose my own special moments of listening to music or playing the piano, and the memories that they can evoke.