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1. Neural Response Selectivity to Natural Sounds in the Bat Midbrain

   https://doi.org/10.1016/j.neuroscience.2019.11.047  

   Salles, A.; Park, S.; Sundar, H.; Macias, S.; Elhilali, M.; Moss, C.F. (May 2020, Neuroscience)

   Little is known about the neural mechanisms that mediate differential action–selection responses to communication and echolocation calls in bats. For example, in the big brown bat, frequency modulated (FM) food-claiming communication calls closely resemble FM echolocation calls, which guide social and orienting behaviors, respectively. Using advanced signal processing methods, we identified fine differences in temporal structure of these natural sounds that appear key to auditory discrimination and behavioral decisions. We recorded extracellular potentials from single neurons in the midbrain inferior colliculus (IC) of passively listening animals, and compared responses to playbacks of acoustic signals used by bats for social communication and echolocation. We combined information obtained from spike number and spike triggered averages (STA) to reveal a robust classification of neuron selectivity for communication or echolocation calls. These data highlight the importance of temporal acoustic structure for differentiating echolocation and food-claiming social calls and point to general mechanisms of natural sound processing across species. 

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2. Axon initial segment plasticity caused by auditory deprivation degrades time difference sensitivity in a model of neural responses to cochlear implants

   https://doi.org/10.1007/s10827-025-00902-9  

   Jing, Anna; Xi, Sylvia; Fransazov, Ivan; Goldwyn, Joshua H (April 2025, Journal of Computational Neuroscience)

   Abstract Synaptic and neural properties can change during periods of auditory deprivation. These changes may disrupt the computations that neurons perform. In the brainstem of chickens, auditory deprivation can lead to changes in the size and biophysics of the axon initial segment (AIS) of neurons in the sound source localization circuit. This is the phenomenon of axon initial segment (AIS) plasticity. Individuals who use cochlear implants (CIs) experience periods of hearing loss, and so we ask whether AIS plasticity in neurons of the medial superior olive (MSO), a key stage of sound location processing, would impact time difference sensitivity in the scenario of hearing with cochlear implants. The biophysical changes that we implement in our model of AIS plasticity include enlargement of the AIS and replacement of low-threshold potassium conductance with the more slowly-activated M-type potassium conductance. AIS plasticity has been observed to have a homeostatic effect with respect to excitability. In our model, AIS plasticity has the additional effect of converting MSO neurons from phasic firing type to tonic firing type. Phasic firing is known to have greater temporal sensitivity to coincident inputs. Consistent with this, we find AIS plasticity degrades time difference sensitivity in the auditory deprived MSO neuron model across a range of stimulus parameters. Our study illustrates a possible mechanism of cellular plasticity in a non-peripheral stage of neural processing that could impose barriers to sound source localization by bilateral cochlear implant users. 

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3. Sound evoked Fos-like immunoreactivity in the big brown bat

   https://doi.org/10.1016/j.ibneur.2022.02.005  

   Salles, A. (January 2022, IBRO neuroscience reports)

   Most bat species have highly developed audio-vocal systems, which allow them to adjust the features of echolocation calls that are optimized for different sonar tasks, such as detecting, localizing, discriminating and tracking targets. Furthermore, bats can also produce a wide array of social calls to communicate with conspecifics. The acoustic properties of some social calls differ only subtly from echolocation calls, yet bats have the ability to distinguish them and reliably produce appropriate behavioral responses. Little is known about the underlying neural processes that enable the correct classification of bat social communication sounds. One approach to this question is to identify the brain regions that are involved in the processing of sounds that carry behavioral relevance. Here, we present preliminary data on neuronal activation, as measured by c-fos expression, in big brown bats (Eptesicus fuscus) exposed to either social calls, echolocation calls or kept in silence. We focused our investigation on five relevant brain areas; three within the canonical auditory pathway (auditory cortex, inferior colliculus and medial geniculate body) and two that are involved in the processing of emotive stimulus content (amygdala and nucleus accumbens). In this manuscript we report c-fos staining of the areas of interest after exposure to conspecific calls. We discuss future work designed to overcome experimental limitations and explore whether c-fos staining reveals anatomical segregation of neurons activated by echolocation and social call call categories. 

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4. Sensorimotor Integration in the Biosonar System of Horseshoe Bats

   Sutlive, Joseph; Riquimaroux, Hiroshi; Mueller, Rolf (November 2017, Society for Neuroscience symposia)

   Bats have evolved unique methods of perception to navigate and catch prey using ultrasonic sounds. It has been observed that the greater horseshoe bat (Rhinolophus ferrumequinum) rapidly move their pinna and noseleaf structures in coordination with pulse emission and echo reception during echolocation, with everything occurring on a 100ms time scale. Sensorimotor integration is not uncommon in neural systems but bats provide a unique case for auditory processing coinciding motion in the periphery. We have developed biomimetic robotic models to replicate the dynamic emission and reception elements of bat echolocation; current data have shown these dynamics introduce time-variant effects which encode information to inform object identification and location. We have planned experiments to understand how motor and auditory systems are integrated, which will be done by recording midbrain responses interacting with stimuli. These recordings will consist of field potential measurements taken from the inferior and superior colliculi; we hope this work will provide physiological events associated with sensorimotor integration for echolocation. 

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5. Active head rolls enhance sonar-based auditory localization performance

   https://doi.org/10.1371/journal.pcbi.1008973  

   Wijesinghe, Lakshitha P.; Wohlgemuth, Melville J.; So, Richard H.; Triesch, Jochen; Moss, Cynthia F.; Shi, Bertram E. (May 2021, PLOS Computational Biology)

   Thaler, Lore (Ed.)

   Animals utilize a variety of active sensing mechanisms to perceive the world around them. Echolocating bats are an excellent model for the study of active auditory localization. The big brown bat ( Eptesicus fuscus ), for instance, employs active head roll movements during sonar prey tracking. The function of head rolls in sound source localization is not well understood. Here, we propose an echolocation model with multi-axis head rotation to investigate the effect of active head roll movements on sound localization performance. The model autonomously learns to align the bat’s head direction towards the target. We show that a model with active head roll movements better localizes targets than a model without head rolls. Furthermore, we demonstrate that active head rolls also reduce the time required for localization in elevation. Finally, our model offers key insights to sound localization cues used by echolocating bats employing active head movements during echolocation. 

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