Revealing The Emotional Life of Bats
Only a scientist who realizes bats have an emotional life can see a link between these flying mammals and post-traumatic stress disorder (PTSD) in soldiers returning from Afghanistan and Iraq.
That researcher is Jagmeet Kanwal, PhD, who heads the Laboratory for Auditory Communication & Cognition in the Departments of Neurology and Neuroscience at GUMC. He says that sounds are processed in the brain’s emotional center, which filters out most of the noise that is not relevant for survival. So in the same way that a bat pays attention to cries of anger and warning from other bats, soldiers listen for sounds that signify danger. A terrifying experience, however, can result in hypersensitivity to sounds that only mimic a threat.
“Some sounds communicate danger and have an emotional impact. Emotions are designed for survival,” Kanwal says. The world humans and animals experience depends entirely on how sensory stimuli are perceived and processed through an emotional filter, he says.
Kanwal’s research has been in the news a lot of late. The work he and his graduate students have done on how bat brains process sound, which was presented in November at the Society for Neuroscience (SFN), has been featured in the New York Times and on National Public Radio. The 2010 book he co-wrote with neuropsychologist Karen Shanor, PhD – Bats Sing, Mice Giggle: The Surprising Science of Animals’ Inner Lives – is backordered at Amazon due to its popularity.
In the book, he and Shanor talk about how many behavioral and mental traits considered uniquely human are in fact shared with other species.
For example, in one passage they say: Four-to-eight week-old bat pups make long strings of barks, chatters and screeches that represent jumbled-up adult-like calls. Scientists now know that bats, like some primates and birds, babble as babies; and the ability to babble can even be accompanied by giggling. Not only do human infants babble and giggle as they experience feelings and try out their audiovocal abilities, so do babies of other species. New and sophisticated technology is taking our understanding into the secret world of animals where we can detect first-hand bats and mice that do indeed sing.
Kanwal has reached his conclusions through exacting research – scientific experiments that involve tracking stimulus-driven responses of single neurons in an animal’s brain.
In some ways, his background sets him up for the painstaking work that he does. He is a Sikh who says that one of the most important tenents of his religion is the search for truth. “I feel in some ways I am seeking truth through science,” he says: decoding the activity of individual neurons in an animal’s brain is a precise, elemental form of basic discovery.
Kanwal grew up in New Delhi, India, went to a high school run by Jesuits and Irish teachers, obtained his undergraduate degree from Delhi University and then came to the U.S. in 1979 to attend Louisiana State University (LSU). He became interested in the newly burgeoning field of brain science, but approached it more as a biologist and naturalist would. “As a bird watcher, I am interested in observing behavior,” he says.
With a PhD in Physiology and Zoology, Kanwal became a neuroethologist, a newly formed discipline that combined neuroscience with the study of natural behavior. Neuroethologists figure out how the brain and central nervous system translate sensory stimuli into species-specific behaviors.
His doctoral thesis at LSU and early postdoctoral work at the University of Colorado was in chemoreception in catfish, where he discovered taste centers in the forebrains of these fish. Then, as a senior research associate and later Assistant Professor at Washington University in St. Louis, he turned to bats, a favorite model system for examining the auditory system. But whereas many researchers study echolocation in bats to understand how they navigate and hunt for insects, Kanwal was interested in social communication in these animals.
His research really took off when he came to GUMC in 1996 because it has a powerful MRI machine devoted only to animal research – one of very few universities to have such a resource, Kanwal says. But use of this device often comes at the price of a lot of banging noise, which could be terrifying to bats, Kanwal says. And then he discovered something “beautiful”– bats, which mostly tune in ultrasonic frequencies, could not hear the sounds made by MRI. Kanwal became the first researcher to image an awake animal inside an MRI magnet. “The bats remained perfectly calm,” he says.
Kanwal says he and his co-workers are now cracking the code for the neural representation of social calls within and between the two cerebral hemispheres and in the amygdala, the seat of emotion.
In research presented at SFN, he and doctoral candidate Bridget Queenan described how it is that mustached bats can attend to a communication within the cacophony of echolocation sounds of hundreds of bats – a phenomenon known as the “cocktail party effect.” They showed that some neurons activated by echolocation sounds tell others to "shush" until communication by a mate makes the shushed neurons "yell louder" than they would in background of silence. This makes the communication sound heard above the din.
Understanding this effect may help patients suffering from certain mental disorders, Kanwal explains. “My fascination, interest, excitement is to understand basic mechanisms, but there are almost always applications to human disorders down the road. We are all connected – the mechanisms that exist in our brains exist in all mammals, birds, fishes. That is where we got them from in the first place.”
“Most of the sounds a person hears do not reach the amygdala because they are unrelated to survival, but sensitivity to many sounds increases in soldiers whose senses are constantly alerted by danger,” Kanwal says. What happens in PTSD is that this protective mechanism degrades, allowing more sound input to the amygdala that triggers the body’s fight or flight reaction. In the face of clear and present danger, the brain adapts by becoming sensitized so that when a soldier hears a sound that is like a gunshot, but isn’t gunshot, “the body over-reacts quickly. The heart and breathing speeds up, the pupils dilate, blood rushes to the muscles, the human is ready to either fight or flee,” he says.
While exposure to these sounds in a safe environment can help soldiers “unlearn” their emotional reaction to them - clinical therapy that is now offered for PTSD – it may also be possible to control the neurotransmitters and their receptors that lead to chronic auditory overstimulation, Kanwal says. Alternately, it may be possible to pinpoint genes that may predispose soldiers to developing PTSD, he says. “Gene expression controls brain circuits, so if we know the basic mechanisms of emotional responses to sound, and the genes that control them, we may be able to understand and treat PTSD at a fundamental level.”
Another trick in his bag is to directly combat the effect of fearful sounds with the presentation of soothing musical sounds. “We plan to compose music specially for this purpose with the help of a member of the National Symphony Orchestra,” he says.
Click here to listen to bat calls.
By Renee Twombly, GUMC Communications