Synesthesia

Death Is a Synesthete (In The Book Thief by Mark Zusak)

Studying synesthesia could lead to therapies for brain diseases

Posted Dec 03, 2013

On Black Friday, instead of shopping, I finished reading Mark Zusak’s The Book Thief.  It was an excellent book, just the kind of mental vacation I wanted to take over the Thanksgiving holiday.  I am not going to review the book here, obviously. This blog is about science.

What made The Book Thief merit the adjective “excellent” from me was not the gripping story.  Instead, it was the narrator, Death. Zusak personifies Death and also makes him/her a synesthete. 

Synesthetes experience the world differently. A sound is not just heard; it might be seen as a color. 

From the prologue of The Book Thief:

The question is, what color will everything be at that moment when I come for you?  What will the sky be saying? 

Personally, I like a chocolate-colored sky. Dark, dark chocolate. People say it suits me. I do, however, try to enjoy every color I see—the whole spectrum. A billion or so flavors, none of them quite the same, and a sky to slowly suck on. 

Death notices the color of the sky when people die but does not see it as a color.  Color is tasted.

Synesthesia is a brain condition where the physical senses overlap. There are around 80 billion neurons in the brain, and each has on average 10 thousand synapses, or connections to other neurons.  As the brain develops, there are bound to be random “wiring errors,” such as faulty, non-existent, or atypical connections between brain areas.

One such wiring error is synesthesia, a benign neurological condition. In the synesthetic brain, there is atypical communication between sensory areas. These atypical connections either do not exist in non-synesthetes, or are present to a much lesser extent.

Atypical connectivity patterns among sensory systems translates into synesthetes tasting sounds or feeling tactile sensations when viewing colors.  For example, while I might just hear (really good) music when I listen to Stevie Nicks singing “Rhiannon,” a synesthete might taste raspberries or consistently see green corresponding to different musical notes.

Since Oliver Sachs wrote about synesthesia in The Man Who Mistook His Wife for a Hat, scientists have carefully studied this condition. 

Neuroscientist David Eagleman at Baylor College of Medicine and his lab created an online questionnaire to identify synesthetes.  Work from his lab identified different kinds of synesthetes and also suggested the existence of corresponding genetic signatures. 

Eagleman’s group is working on high-throughput neuroimaging studies of synesthetes, and hopefully the Human Connectome Project will include synesthetes at some point as well.

Because synesthesia involves the sensory systems, studying it could provide a unique opportunity to map out how, and maybe when, connections go awry in the brain. Neuroscience knows a lot about the sensory systems.  It could be argued that neuroscience knows the most about the sensory systems.  Starting in the 1960s, the somatosensory and visual systems were meticulously mapped out by neuroscience greats like Vernon Mountcastle and David Van Essen.

Map of the visual system, from Felleman, D.J. and Van Essen, D.C. (1991) Cerebral Cortex, 1: 1-47.

There are numerous parallels between the sensory systems of humans and other animals, and there are detailed connectivity maps of sensory systems.  A map of the visual system is shown.  

A similar wealth of knowledge has not yet been attained for social cognition, which is where the human brain allocates the vast majority of its resources.  Understanding wiring patterns in synesthetic brains could lead to a model that is applicable to other brain connectivity conditions, such as social cognition disorders like the autism spectrum or mental health diseases like schizophrenia.

I have not yet seen the film adaptation of The Book Thief that came out in early November, but so far the movie reviews I have read are not flattering like I expected.

One review I read used the word “smarmy” to describe the narrator. I found the novel text convincing—like I said, reading the book was a vacation—so I wonder if the movie does not do synesthesia justice?  That would be disappointing since synesthesia is a harmless and fascinating neurological condition, and one that, when science figures out how it arises in the brain, could lead to therapies for brain diseases.