Dr. Melissa Caras
Assistant Professor, University of Maryland
Postdoctoral Fellow, New York University
PhD, Univrersity of Washington
Dr. Melissa Caras first encountered the word “neuroscientist” at 15 years old while watching a documentary about autism. It appeared briefly—just a caption beneath an expert’s name. She spent the rest of the day fascinated as she learned everything she could about neuroscience, and she promptly declared to her parents that someday she was going to be a neuroscientist, too. The title that once flashed across her screen now belongs to her. As an Assistant Professor of Biology at the University of Maryland, Melissa studies how the brain learns to perceive sound.
Since that fateful day as a teenager, Melissa remained steadfast in her goal. At Brandeis University, she double majored in neuroscience and biology, and she had the rare opportunity to participate in lab research all four years of her undergraduate studies. As a freshman, Melissa took an introductory psychology class where she first learned about qualia—the internal, subjective component of sensory perception. For example, the experience of “redness” when looking at a fire engine is not measurable or observable by others— “red” is how we describe our perception of the wavelengths of light reflecting off the paint. “That blew my mind, and I became very interested in sensation and perception,” she says. Inspired, she joined the lab of Dr. Donald Katz, who studied taste sensation and perception. In the lab, Melissa was encouraged to pursue her own project, an investigation into the role of serotonin in taste perception. She found that in rats, serotonergic signaling regulated salt intake by modulating thirst, but had no impact on salt perception. The project became Melissa’s thesis and her first paper, a rare accomplishment for an undergraduate.
Melissa was already having a blast doing neuroscience research at Brandeis, so when she learned from her lab mates that PhD students get paid during their training, she thought, “That’s the best deal ever! Are you kidding?” and decided to apply to PhD programs. Her experience working with rats in tightly controlled lab settings spurred an interest in neuroethology—the study of how the brain functions in naturalistic settings. On the advice of the renowned neuroethologist Dr. Eve Marder, also at Brandeis, she applied to the University of Washington, where many labs aimed for more realistic experimental environments. In addition, after interviewing at several places, she came to appreciate UW's vibrant student culture and the stunning landscapes of the Pacific Northwest.
After three rotations, Melissa embarked upon a collaborative project studying the influence of seasonal hormonal fluctuations on the auditory system in songbirds. She was co-supervised by Drs. Eliot Brenowitz and Edwin Rubel, and her project combined their respective expertise on songbird neurobiology and auditory system electrophysiology. Melissa focused on the influence of seasonally timed hormone cycles on the auditory system of the white-crowned sparrow, a small songbird with a migration pattern spanning most of the northern hemisphere. Their migrations force them to precisely time their breeding, a process that requires sensitive perception of their mate’s songs. Melissa hypothesized that seasonally fluctuating hormones might modulate auditory sensitivity, helping females recognize potential mates at just the right time. By manipulating light-dark cycles and hormone levels to mimic the birds’ natural breeding seasons, Melissa found that elevated estradiol levels in females enhanced their neural responses to sound. These findings offered insight into how seasonal shifts in internal physiological states can tune sensory systems. Since Melissa was limited to only recording from anesthetized birds, she was determined to find a postdoctoral project that would incorporate a behavioral component.
After she graduated from UW, Melissa began a postdoc with Dr. Dan Sanes at NYU, studying auditory neuroplasticity in gerbils. She sought to investigate conductive hearing loss, where transient loss of acoustic input—for instance, because of earwax buildup or an ear infection—permanently changes the development of inner ear pathways that transduce sounds into neural signals. Melissa wanted to know if these changes went beyond the wiring of the auditory system—did conductive hearing loss affect sound perception too? The clinical relevance of such a question was clear: in humans, infants and toddlers who experience multiple ear infections and hearing impairment are at greater risk for speech and language delays. Melissa first replicated this behavioral effect in gerbils performing a perceptual learning task. In this task, gerbils were trained to detect tiny amplitude fluctuations in a noisy sound. Normally, their detection improves with practice, and they can learn to identify increasingly smaller amplitude modulations (AMs), like how an expert musician can discern between the sounds of a high-quality instrument and a cheap one. However, gerbils whose ears were plugged briefly as pups displayed abnormal perception behavior. First, they couldn’t detect smaller AMs as well as their healthy littermates. Second, some of the gerbils who were earplugged as pups displayed altered learning trajectories. These results suggested that their perceptual learning was disrupted by the intervention.
This result inspired Melissa to investigate the neural basis of perceptual learning. She aimed to bridge the brain-behavior gap by linking longitudinal changes in neural responses with the behavioral improvements seen as an organism learns. Melissa recorded from the auditory cortex of normal-hearing gerbils for several days as they learned how to perform an AM detection task, like the one she used previously. First, she showed that gerbils improved on the task with practice. Then, she observed that the gerbils’ neural responses became more sensitive to smaller AMs over time. The rate that neural responses sensitized and the rate that gerbils’ detection improved were correlated, suggesting a neurobehavioral learning process. However, this correlation was only observed when the gerbils were actively engaged with the task—passively listening to the sounds still produced neural responses, but their amplitudes weren’t correlated with behavior. Why would the animal’s engagement with the task change the trajectory of neural responses to the same sounds? Melissa hypothesized that the neural mechanism of perceptual learning in the auditory cortex was being gated by another brain region that modulated learning in a task-dependent manner. Finding the brain region that controlled this “top-down” gating effect inspired her future lab’s research.
Now as an Assistant Professor at the University of Maryland, Melissa’s lab aims to uncover how perceptual learning is implemented in the brain. Specifically, how does neural circuitry enable the transformation in behavior between a perceptual novice and an expert? Using sound-guided behavior in gerbils and techniques like in vivo electrophysiology and anatomical tracing, her lab has studied brain regions like the orbitofrontal cortex (OFC). The OFC is particularly interesting for perceptual learning because it receives projections from all sensory regions, including the auditory system. Looking forward, Melissa hopes to extend her perceptual learning research into models of hearing loss in aging, or even into other non-mammal species, like the songbirds she studied during her PhD.
Melissa’s trajectory in her scientific career has been quite linear, and she describes her experience as overwhelmingly positive. With good mentors, good networking, and good luck, even being on the job market can be enjoyable. She thinks that we often hear too much about how hard it is to succeed in science, as the stories that get posted on social media are often skewed towards negativity. “The good experiences don’t get spoken about enough. You really can have fun!” Melissa’s optimism, hard work, and passion for the brain have led to her achieving the career she always dreamed of, and she’s had a great time doing it.
Find out more about Melissa and her lab’s research here.
Listen to Meenakshi’s full interview with Melissa on March 3, 2025 below!
