About

Dr. Melissa Caras is an assistant professor in the Department of Biology at the University of Maryland. Her research program seeks to reveal the neural basis for auditory perception, with a specific focus on experience-dependent plasticity. She explores how training-based improvements in sensory facilities are implemented in the brain by measuring and manipulating neural circuit activation in freely-moving, behaving animals, primarily focusing on plasticity in auditory and top-down modulatory networks. Her laboratory employs advanced approaches such as wireless recordings from multichannel electrode arrays, optogenetics, targeted infusions of pharmacological agents, neuroanatomical tracing, and quantitative animal behavior. Prior to her current position, Dr. Caras completed postdoctoral training at New York University’s Center for Neural Science, where she examined the central consequences of developmental hearing loss. She earned her Ph.D. at the University of Washington in Seattle, where she studied the impact of sex-steroid hormones on auditory processing in wild-caught songbirds. Her work emphasizes the importance of perceptual learning in shaping complex behaviors like speech and language, and she investigates how training-induced neural plasticity occurs within auditory and top-down networks.

Research topics

• Neuroscience
• Psychology
• Biology
• Audiology
• Cognitive psychology

Selected publications

• Total internal reflection waveguide for depth-selective light delivery

  2026-03-05

  article

  Photostimulation with optical fiber implants delivers sufficient optical power deep in brain tissue but sacrifice spatial precision control and depth selectivity. We present a 3D-printed “staircase” waveguide containing total internal reflection micro mirrors that allow switchable light guiding to user-defined depths with minimal divergence. We demonstrated six discrete output depths in 220µm–1.5mm covering the cortical layers of rodent models, with transmission efficiency of 60% and each beam remained less than 150um in diameter after 1 mm propagation.

  PublisherDOI

• Neural Correlates of Perceptual Plasticity in the Auditory Midbrain and Thalamus

  Journal of Neuroscience · 2025-01-03 · 4 citations

  articleOpen accessSenior author

  Hearing is an active process in which listeners must detect and identify sounds, segregate and discriminate stimulus features, and extract their behavioral relevance. Adaptive changes in sound detection can emerge rapidly, during sudden shifts in acoustic or environmental context, or more slowly as a result of practice. Although we know that context- and learning-dependent changes in the sensitivity of auditory cortical (ACX) neurons support many aspects of perceptual plasticity, the contribution of subcortical auditory regions to this process is less understood. Here, we recorded single- and multiunit activity from the central nucleus of the inferior colliculus (ICC) and the ventral subdivision of the medial geniculate nucleus (MGV) of male and female Mongolian gerbils under two different behavioral contexts: as animals performed an amplitude modulation (AM) detection task and as they were passively exposed to AM sounds. Using a signal detection framework to estimate neurometric sensitivity, we found that neural thresholds in both regions improve during task performance, and this improvement is largely driven by changes in the firing rate rather than phase locking. We also found that ICC and MGV neurometric thresholds improve as animals learn to detect small AM depths during a multiday perceptual training paradigm. Finally, we revealed that in the MGV, but not the ICC, context-dependent enhancements in AM sensitivity grow stronger during perceptual training, mirroring prior observations in the ACX. Together, our results suggest that the auditory midbrain and thalamus contribute to changes in sound processing and perception over rapid and slow timescales.

  PublisherOA PDFDOI

• Orbitofrontal cortex modulates auditory cortical sensitivity and sound perception in Mongolian gerbils

  Current Biology · 2024-07-11 · 8 citations

  articleOpen accessSenior author
  PublisherOA PDFDOI

• Neural correlates of flexible sound perception in the auditory midbrain and thalamus

  bioRxiv (Cold Spring Harbor Laboratory) · 2024-04-12 · 1 citations

  preprintOpen accessCorresponding

  Abstract Hearing is an active process in which listeners must detect and identify sounds, segregate and discriminate stimulus features, and extract their behavioral relevance. Adaptive changes in sound detection can emerge rapidly, during sudden shifts in acoustic or environmental context, or more slowly as a result of practice. Although we know that context- and learning-dependent changes in the spectral and temporal sensitivity of auditory cortical neurons support many aspects of flexible listening, the contribution of subcortical auditory regions to this process is less understood. Here, we recorded single- and multi-unit activity from the central nucleus of the inferior colliculus (ICC) and the ventral subdivision of the medial geniculate nucleus (MGV) of Mongolian gerbils under two different behavioral contexts: as animals performed an amplitude modulation (AM) detection task and as they were passively exposed to AM sounds. Using a signal detection framework to estimate neurometric sensitivity, we found that neural thresholds in both regions improved during task performance, and this improvement was driven by changes in firing rate rather than phase locking. We also found that ICC and MGV neurometric thresholds improved and correlated with behavioral performance as animals learn to detect small AM depths during a multi-day perceptual training paradigm. Finally, we reveal that in the MGV, but not the ICC, context-dependent enhancements in AM sensitivity grow stronger during perceptual training, mirroring prior observations in the auditory cortex. Together, our results suggest that the auditory midbrain and thalamus contribute to flexible sound processing and perception over rapid and slow timescales. Significance statement What a listener hears depends on several factors, such as whether the listener is attentive or distracted, and whether the sound is meaningful or irrelevant. Practice can also shape hearing by improving the detection of particular sound features, as occurs during language or musical learning. Understanding how changes in sound perception are implemented in the brain is important for developing strategies to optimize healthy hearing, and for treating disorders in which these processes go awry. We report that neurons in auditory midbrain and thalamus exhibit rapid shifts in sound sensitivity that depend on the sound’s behavioral relevance, and slower improvements that emerge over several days of training. Our results suggest that subcortical areas make an important contribution to flexible hearing.

  PublisherOA PDFDOI

• Orbitofrontal Cortex Modulates Auditory Cortical Sensitivity and Sound Perception

  bioRxiv (Cold Spring Harbor Laboratory) · 2023-12-18 · 1 citations

  preprintOpen accessSenior author

  Sensory perception is dynamic, quickly adapting to sudden shifts in environmental or behavioral context. Though decades of work have established that these dynamics are mediated by rapid fluctuations in sensory cortical activity, we have a limited understanding of the brain regions and pathways that orchestrate these changes. Neurons in the orbitofrontal cortex (OFC) encode contextual information, and recent data suggest that some of these signals are transmitted to sensory cortices. Whether and how these signals shape sensory encoding and perceptual sensitivity remains uncertain. Here, we asked whether the OFC mediates context-dependent changes in auditory cortical sensitivity and sound perception by monitoring and manipulating OFC activity in freely moving animals under two behavioral contexts: passive sound exposure and engagement in an amplitude modulation (AM) detection task. We found that the majority of OFC neurons, including the specific subset that innervate the auditory cortex, were strongly modulated by task engagement. Pharmacological inactivation of the OFC prevented rapid context-dependent changes in auditory cortical firing, and significantly impaired behavioral AM detection. Our findings suggest that contextual information from the OFC mediates rapid plasticity in the auditory cortex and facilitates the perception of behaviorally relevant sounds. Significance Statement: Sensory perception depends on the context in which stimuli are presented. For example, perception is enhanced when stimuli are informative, such as when they are important to solve a task. Perceptual enhancements result from an increase in the sensitivity of sensory cortical neurons; however, we do not fully understand how such changes are initiated in the brain. Here, we tested the role of the orbitofrontal cortex (OFC) in controlling auditory cortical sensitivity and sound perception. We found that OFC neurons change their activity when animals perform a sound detection task. Inactivating OFC impairs sound detection and prevents task-dependent increases in auditory cortical sensitivity. Our findings suggest that the OFC controls contextual modulations of the auditory cortex and sound perception.

  PublisherOA PDFDOI

• Organization of orbitofrontal‐auditory pathways in the Mongolian gerbil

  The Journal of Comparative Neurology · 2023-07-21 · 9 citations

  articleOpen accessSenior author

  Sound perception is highly malleable, rapidly adjusting to the acoustic environment and behavioral demands. This flexibility is the result of ongoing changes in auditory cortical activity driven by fluctuations in attention, arousal, or prior expectations. Recent work suggests that the orbitofrontal cortex (OFC) may mediate some of these rapid changes, but the anatomical connections between the OFC and the auditory system are not well characterized. Here, we used virally mediated fluorescent tracers to map the projection from OFC to the auditory midbrain, thalamus, and cortex in a classic animal model for auditory research, the Mongolian gerbil (Meriones unguiculatus). We observed no connectivity between the OFC and the auditory midbrain, and an extremely sparse connection between the dorsolateral OFC and higher order auditory thalamic regions. In contrast, we observed a robust connection between the ventral and medial subdivisions of the OFC and the auditory cortex, with a clear bias for secondary auditory cortical regions. OFC axon terminals were found in all auditory cortical lamina but were significantly more concentrated in the infragranular layers. Tissue-clearing and lightsheet microscopy further revealed that auditory cortical-projecting OFC neurons send extensive axon collaterals throughout the brain, targeting both sensory and non-sensory regions involved in learning, decision-making, and memory. These findings provide a more detailed map of orbitofrontal-auditory connections and shed light on the possible role of the OFC in supporting auditory cognition.

  PublisherOA PDFDOI

• Organization of orbitofrontal-auditory pathways in the Mongolian gerbil

  bioRxiv (Cold Spring Harbor Laboratory) · 2023-04-28 · 1 citations

  preprintOpen accessSenior author

  Abstract Sound perception is highly malleable, rapidly adjusting to the acoustic environment and behavioral demands. This flexibility is the result of ongoing changes in auditory cortical activity driven by fluctuations in attention, arousal, or prior expectations. Recent work suggests that the orbitofrontal cortex (OFC) may mediate some of these rapid changes, but the anatomical connections between the OFC and the auditory system are not well-characterized. Here, we used virally-mediated fluorescent tracers to map the projection from OFC to the auditory midbrain, thalamus, and cortex in a classic animal model for auditory research, the Mongolian gerbil ( Meriones unguiculatus ). We observed no connectivity between the OFC and the auditory midbrain, and an extremely sparse connection between the dorsolateral OFC and higher-order auditory thalamic regions. In contrast, we observed a robust connection between the ventral and medial subdivisions of the OFC and the auditory cortex, with a clear bias for secondary auditory cortical regions. OFC axon terminals were found in all auditory cortical lamina but were significantly more concentrated in the infragranular layers. Tissue-clearing and lightsheet microscopy further revealed that auditory cortical-projecting OFC neurons send extensive axon collaterals throughout the brain, targeting both sensory and non-sensory regions involved in learning, decision-making, and memory. These findings provide a more detailed map of orbitofrontal-auditory connections and shed light on the possible role of the OFC in supporting auditory cognition.

  PublisherOA PDFDOI

• Non-sensory Influences on Auditory Learning and Plasticity

  Journal of the Association for Research in Otolaryngology · 2022-03-02 · 4 citations

  reviewOpen access1st authorCorresponding
  PublisherOA PDFDOI

• Editorial: Mechanisms Underlying Experience-Dependent Plasticity of Cortical Circuits

  Frontiers in Cellular Neuroscience · 2021-04-30 · 4 citations

  editorialOpen access

  EDITORIAL article Front. Cell. Neurosci., 30 April 2021 | https://doi.org/10.3389/fncel.2021.687297

  PublisherOA PDFDOI

• Neural Variability Limits Adolescent Skill Learning

  Journal of Neuroscience · 2019-02-12 · 38 citations

  articleOpen access1st authorCorresponding

  Skill learning is fundamental to the acquisition of many complex behaviors that emerge during development. For example, years of practice give rise to perceptual improvements that contribute to mature speech and language skills. While fully honed learning skills might be thought to offer an advantage during the juvenile period, the ability to learn actually continues to develop through childhood and adolescence, suggesting that the neural mechanisms that support skill learning are slow to mature. To address this issue, we asked whether the rate and magnitude of perceptual learning varies as a function of age as male and female gerbils trained on an auditory task. Adolescents displayed a slower rate of perceptual learning compared with their young and mature counterparts. We recorded auditory cortical neuron activity from a subset of adolescent and adult gerbils as they underwent perceptual training. While training enhanced the sensitivity of most adult units, the sensitivity of many adolescent units remained unchanged, or even declined across training days. Therefore, the average rate of cortical improvement was significantly slower in adolescents compared with adults. Both smaller differences between sound-evoked response magnitudes and greater trial-to-trial response fluctuations contributed to the poorer sensitivity of individual adolescent neurons. Together, these findings suggest that elevated sensory neural variability limits adolescent skill learning. SIGNIFICANCE STATEMENT The ability to learn new skills emerges gradually as children age. This prolonged development, often lasting well into adolescence, suggests that children, teens, and adults may rely on distinct neural strategies to improve their sensory and motor capabilities. Here, we found that practice-based improvement on a sound detection task is slower in adolescent gerbils than in younger or older animals. Neural recordings made during training revealed that practice enhanced the sound sensitivity of adult cortical neurons, but had a weaker effect in adolescents. This latter finding was partially explained by the fact that adolescent neural responses were more variable than in adults. Our results suggest that one mechanistic basis of adult-like skill learning is a reduction in neural response variability.

  PublisherOA PDFDOI

Recent grants

• Significant Life Event Supplement-Neural mechanisms of auditory plasticity and perceptual learning

  NIH · $937k · 2017–2023

• The Effects of Reversible Hearing Loss on the Development of Auditory Perception and Neural Coding

  NIH · $141k · 2015–2018

• Non-sensory Circuits for Auditory Perceptual Learning

  NIH · $2.0M · 2023–2027

• Cortical Mechanisms Supporting Auditory Perceptual Learning

  NIH · $263k · 2017–2019

• NIH Grant F31DC010938

  NIH · $98k · 2013

Frequent coauthors

• Eliot A. Brenowitz

  University of Washington

  11 shared

• Dan H. Sanes

  New York University

  8 shared

• Edwin W. Rubel

  University of Washington

  7 shared

• Tracy A. Larson

  University of Virginia

  5 shared

• David J. Perkel

  University of Washington

  5 shared

• Nivretta Thatra

  5 shared

• William E. Wood

  University of California, Berkeley

  4 shared

• Karin Lent

  University of Washington

  4 shared

Education

• Ph.D., Neurobiology and Behavior

  University of Washington

  2013

• B.S.

  Brandeis University

  2007