Among the inhabitants of my household is a five-year-old pug, Alfred. After a somewhat rocky start, my relationship with Alfred has blossomed: When I return home—much less feed him or take him for a walk—he scampers around appreciatively, snarling and grunting in the manner I’ve come to associate with the expression of canine excitement. But any fondness that Alfred holds for me is far eclipsed by his relationship with my wife, with whom he has lived his entire life. When she leaves home, Alfred wanders the apartment listlessly before finally taking up a spot that affords him an unobstructed view of the front door. And there he sits, staring intently, alert to the faintest hint of his rightful owner’s return. Reflecting on his behavior, my wife and I often find ourselves speaking of how worried poor Alfie seems in her absence; occasionally, in a fit of diagnostic excess, we declare that he is suffering from separation anxiety.
As a historian of philosophy and mental health, such talk leaves me uneasy. What does it mean to say that an animal, even one as keenly attuned to its surroundings as Alfred, is apprehensive or concerned? Surely the experience of such states requires a capacity for self-reflection lacking in animals. Isn’t my speculation about Alfred’s psychological states just the crudest anthropomorphic sentimentality? My wife has no such qualms. Alfred is anxious; what more is there to say?
Quite a lot, it would seem, at least according to Joseph LeDoux’s Anxious. Currently the Henry and Lucy Moses Professor of Science at New York University, LeDoux has been grappling for the better part of the last four decades with questions of how emotions are processed by human and animal brains. As a graduate student at the State University of New York at Stony Brook in the mid-1970s, LeDoux and his supervisor, Michael Gazzaniga, conducted pioneering research on patients with split-brain syndrome, a condition in which the flow of information between the two hemispheres of the brain is disrupted, resulting in profound shifts in behavior. Based on their experiments, LeDoux and Gazzaniga concluded that much of the emotional processing that takes place within the brain occurs nonconsciously—that is to say, prior to the organism becoming actively aware of the stimuli producing the response.
LeDoux’s work on nonconscious emotions led him to take up the question of how the brain processes fear. After carrying out a series of experiments on the brains of rats, his attention was drawn to the amygdalae, two clusters of neurons located deep inside the medial temporal lobe of complex vertebrates such as rodents and humans. LeDoux has been researching and writing about the amygdala ever since; indeed, such is his dedication to all things amygdalar that he even named his rock band, in which he plays guitar and sings, the Amygdaloids (the band is a recurring feature of Anxious).
Though discovered in the early 19th century, the amygdala wasn’t first associated with fear (and, even more, aggression) until the late 1930s, when the neuroscientists Heinrich Klüver and Paul Bucy began experimenting on rhesus monkeys whose temporal lobes—and hence amygdalae—had been removed. Following their lobectomies, the monkeys exhibited less aggression and fear; where before they’d been afraid of humans, now the monkeys approached the doctors without hesitation, even allowing themselves to be touched. Other changes in behavior also followed, including the development of an oral fixation and a marked increase in sexual activity (at times these traits overlapped, with Klüver and Bucy noting that the monkeys would occasionally fall asleep with their erect penises in their mouths). More studies related to the amygdala appeared in the 1950s, but for several decades it remained obscure even to scientists.