Biology subjects

Lauer, A. M.

Publications and source records attributed to Lauer, A. M..

4 recordsLinked to original sources

bioRxiv2025

Revealing hidden knowledge in amnestic mice

Alzheimers disease (AD) is a form of dementia in which memory and cognitive decline is thought to arise from underlying neurodegeneration. These cognitive impairments, however, are transient when they first appear and can fluctuate across disease progression. Here, we investigate the neural mechanisms underlying fluctuations of performance in amnestic mice. We trained APP/PS1+ mice on an auditory go/no-go task that dissociated learning of task contingencies (knowledge) from its more variable expression under reinforcement (performance). APP/PS1+ exhibited significant performance deficits compared to control mice. Using large-scale two-photon imaging of 6,216 excitatory neurons in 8 mice, we found that auditory cortical networks were more suppressed, less selective to the sensory cues, and exhibited aberrant higher-order encoding of reward prediction compared to control mice. A small sub-population of neurons, however, displayed the opposite phenotype, reflecting a potential compensatory mechanism. Volumetric analysis demonstrated that deficits were concentrated near A{beta} plaques. Strikingly, we found that these cortical deficits were reversed almost instantaneously on probe (non-reinforced) trials when APP/PS1+ performed as well as control mice, providing neural evidence for intact stimulus-action knowledge despite variable ongoing performance. A biologically-plausible reinforcement learning model recapitulated these results and showed that synaptic weights from sensory-to-decision neurons were preserved (i.e. intact stimulus-action knowledge) despite poor performance that was due to inadequate contextual scaling (i.e. impaired performance). Our results suggest that the amnestic phenotype is transient, contextual, and endogenously reversible, with the underlying neural circuits retaining the underlying stimulus-action associations. Thus, memory deficits commonly observed in amnestic mouse models, and potentially at early stages of dementia in humans, relate more to contextual drivers of performance rather than degeneration of the underlying memory traces.

neuroscience↗

bioRxiv2025

Early Noise Exposure and Changes in Medial Olivocochlear Strength Alters Auditory Pathway Development

The early onset of peripheral deafness significantly alters the proper development of the auditory system. Likewise, exposure to loud noise during early development produces a similar disruptive effect. Before hearing onset in altricial mammals, cochlear inner hair cells exhibit spontaneous electrical activity that drives auditory circuit development. This activity is modulated by medial olivocochlear (MOC) efferent feedback through 910 nicotinic cholinergic receptors in inner hair cells. In adults, these receptors are restricted to outer hair cells, where they mediate MOC feedback to regulate cochlear amplification. Although the MOC systems protective role to prevent noise-induced hearing loss in adulthood is well-established, its influence during early developmental stages-especially in response to exposure to loud noise-remains largely unexplored. In this study, we investigated the role of MOC feedback during early postnatal development using 9 knockout (KO) and 9 knock-in (KI) mice of either sex, which respectively lack or exhibit enhanced cholinergic activity. Our findings reveal that both increased and absent olivocochlear activity result in altered auditory sensitivity at the onset of hearing, along with long- range alterations in the number and morphology of ribbon synapses. Early noise exposure caused lasting auditory damage in both wild-type and 9KO mice, with deficits persisting into adulthood. In contrast, 9KI mice were protected from noise-induced damage, with no long-term effects on auditory function. These results highlight the increased susceptibility of the auditory system during early postnatal development. Moreover, they indicate that an enhanced MOC feedback shields the auditory system from noise damage during this period. SIGNIFICANCE STATEMENTEarly development represents a sensitive window for shaping auditory function. We show that the medial olivocochlear system is critical for establishing normal ribbon synapse density and size; key features for proper hearing onset. We also show that the developing auditory system is especially vulnerable to loud noise, with early exposure causing more severe and lasting effects than similar noise later in life. Notably, enhancing 910 nAChR receptor activity during this early stage offers protection against noise-induced damage, revealing a time-sensitive opportunity to safeguard auditory development.

neuroscience↗

bioRxiv2024

Resistance to age-related hearing loss in the echolocating big brown bat (Eptesicus fuscus)

Hearing mediates many behaviors critical for survival in echolocating bats, including foraging and navigation. Most mammals are susceptible to progressive age-related hearing loss; however, the evolution of biosonar, which requires the ability to hear low-intensity echoes from outgoing sonar signals, may have selected against the development of hearing deficits in echolocating bats. Although many echolocating bats exhibit exceptional longevity and rely on acoustic behaviors for survival to old age, relatively little is known about the aging bat auditory system. In this study, we used DNA methylation to estimate the ages of wild-caught big brown bats (Eptesicus fuscus) and measured hearing sensitivity in young and aging bats using auditory brainstem responses (ABRs) and distortion product otoacoustic emissions (DPOAEs). We found no evidence for hearing deficits in aging bats, demonstrated by comparable thresholds and similar ABR wave and DPOAE amplitudes across age groups. We additionally found no significant histological evidence for cochlear aging, with similar hair cell counts, afferent, and efferent innervation patterns in young and aging bats. Here we demonstrate that big brown bats show minimal evidence for age-related loss of peripheral hearing sensitivity and therefore represent informative models for investigating mechanisms that may preserve hearing function over a long lifetime.

neuroscience↗

bioRxiv2024

Effects of age on responses of principal cells of the mouse anteroventral cochlear nucleus in quiet and noise

Older listeners often report difficulties understanding speech in noisy environments. It is important to identify where in the auditory pathway hearing-in-noise deficits arise to develop appropriate therapies. We tested how encoding of sounds is affected by masking noise at early stages of the auditory pathway by recording responses of principal cells in the anteroventral cochlear nucleus (AVCN) of aging CBA/CaJ and C57BL/6J mice in vivo. Previous work indicated that masking noise shifts the dynamic range of single auditory nerve fibers (ANFs), leading to elevated tone thresholds. We hypothesized that such threshold shifts could contribute to increased hearing-in-noise deficits with age if susceptibility to masking increased in AVCN units. We tested this by recording the responses of AVCN principal neurons to tones in the presence and absence of masking noise. Surprisingly, we found that masker-induced threshold shifts decreased with age in primary-like units and did not change in choppers. In addition, spontaneous activity decreased in primary-like and chopper units of old mice, with no change in dynamic range or tuning precision. In C57 mice, which undergo early onset hearing loss, units showed similar changes in threshold and spontaneous rate at younger ages, suggesting they were related to hearing loss and not simply aging. These findings suggest that sound information carried by AVCN principal cells remains largely unchanged with age. Therefore, hearing-in-noise deficits may result from other changes during aging, such as distorted across-channel input from the cochlea and changes in sound coding at later stages of the auditory pathway. Significance StatementMiddle age and older listeners commonly experience hearing deficits in the presence of background noise. Central auditory areas have been implicated in hearing-in-noise deficits, but it is not known where these deficits arise. We performed in vivo recordings in mice of different ages at the first stage of the auditory pathway in the brain, the cochlear nucleus, to examine how encoding of sounds is perturbed by masking noise. We found that the responses of individual neurons remain largely intact with age, including the processing of tones in masking noise, despite previously documented structural and physiological degeneration of their auditory nerve inputs. This suggests that problems hearing in masking noise result from changes at other stages of the auditory pathway.

neuroscience↗