Karl Deisseroth’s book comes so richly garlanded with endorsements that I wanted to dislike it. A world-renowned psychiatrist and neuroscientist, Deisseroth is also a talented writer who, when the technology comes up short or the science is found wanting, always seems to have the perfect metaphor or line of poetry to hand. There are times when literature provides “a window on to the brain more informative than any microscope objective”, he writes, peppering each chapter with epigrams from Joyce, Milton and Millay.
Using optogenetics, a technology that renders individual, highly specific brain cells photosensitive and then activates those cells using flashes of light delivered through a fibreoptic wire, Deisseroth’s research focuses on the brain circuits behind everything from our sudden mood swings to behaviour, such as crying, which are unique to humans. Likening these complex axonal connections to “warp threads”, Deisseroth hopes that by using optogenetics to turn these circuits on and off, he can better understand the physiochemical basis of human behaviour and with it the “tapestry of the human story”, by which he means the evolutionary roots of mental illness and emotions such as joy, hope and anxiety.
But Deisseroth is first and foremost an emergency psychiatrist and it is in his encounters with distressed patients that his talent for marrying science and the imagination becomes most apparent and that his writing comes truly alive. In this respect, Connections warrants comparison with books such as Do No Harm by Henry Marsh and Brainstorm by Suzanne Sullivan, physicians for whom, like Deisseroth, medicine is as much an art as a science.
What unites many of the stories in Connections are the eyes. Thus, in the first chapter, Deisseroth introduces us to Andi, a four-year-old girl with a listing left eye and Mateo, a newlywed inexplicably unable to shed tears for his recently deceased bride. In Andi’s case, her crossed eye is a sure sign of a glioma on the pons, the region of the brainstem responsible for a range of functions including respiration, eye movements and the production of tears. Using optogenetics to plumb the mysteries of Mateo’s arid lachrymal glands, Deisseroth is also led to the pons and a region of the amygdala called the BNST involved in the regulation of emotions such as hope and anxiety.
Mateo’s tearless gaze seems to signal the absence of hope. In an ideal word, Deisseroth would continue to question Mateo in order to make sense of the “intertwined thread of the biological, social and psychological” that has brought him to the emergency room. Instead, he has no choice but to move to the next patient. Shedding a tear for himself, as much as for Mateo, Deisseroth speculates that crying might be a recent evolutionary innovation, a way of finding strength and purpose in adversity, hence why we cry alone and in the presence of predators, even though to do so is to signal our vulnerability.
At various points, Deisseroth hints that this is as much a journey into his psyche as those of his patients
Deisseroth offers similarly enriching and tentative insights into the pathways involved in depression and disorders such as mania and bulimia. In juxtaposing the case of a lonely Uyghur woman with a deep need to tell stories about her distant homeland and an autistic man uneasy making eye contact, Deisseroth also illuminates the way that the brain has developed a suite of behaviours and emotional prompts to regulate social interactions and the pain that often accompanies their absence.
Connections is subtitled “a story of human feeling” and by combining his case notes with insights from optogenetics and philosophical disquisitions, Deisseroth achieves the difficult feat of moving and enlightening the reader at the same time. In the process, he succeeds in telling a larger story about the origins of human emotions while illuminating the roots of disorders such as schizophrenia and dementia. However, after a while, his method becomes a little formulaic; each chapter opens with a troubled patient and a revealing anecdote followed by insights from the latest scientific research leavened with personal apercus.
At various points, Deisseroth hints that this is as much a journey into his psyche as those of his patients. “At the heart of every story here, there is a lost child,” he writes towards the end. But, frustratingly, these and other cryptic comments are left hanging (perhaps Deisseroth plans to reveal more in the inevitable sequel).
The end result is a book that is both beautiful to read and packed with cutting-edge science but which, in places, feels a little bit too artful. As with optogenetics itself, the more that Deisseroth strips away the warp threads to reveal the underlying structures governing our emotions, the more we lose sight of the rich tapestry that makes us human and, it would seem, of Deisseroth himself.
• Connections by Karl Deisseroth is published by Viking (£20). To support the Guardian order your copy at guardianbookshop.com. Delivery charges may apply