Induction of selective plasticity in the frequency tuning of auditory cortex and auditory thalamus neurons by locus coeruleus stimulation

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

Sensory perception is dynamic, quickly adapting to sudden shifts in environmental or behavioral context. Although 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 remain 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 Mongolian gerbils of both sexes 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 innervates 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.

Current status of transcutaneous auricular vagus nerve stimulation for tinnitus: a narrative review of modern research

Tinnitus, characterized by phantom sound perception, is a highly disruptive disorder lacking definitive and effective treatments. Its intricate neural mechanisms are not fully understood. Transcutaneous auricular vagus nerve stimulation (taVNS) has demonstrated potential as a substitute or supplementary treatment by activating central vagal pathways. However, standardized therapeutic protocols and objective tests to assess efficacy are lacking. Therefore, taVNS shows promise as a therapy for tinnitus, and treatment protocols should be optimized in future clinical trials.

Sound-evoked adenosine release in cooperation with neuromodulatory circuits permits auditory cortical plasticity and perceptual learning

Meaningful auditory memories are formed in adults when acoustic information is delivered to the auditory cortex during heightened states of attention, vigilance, or alertness, as mediated by neuromodulatory circuits. Here, we identify that, in awake mice, acoustic stimulation triggers auditory thalamocortical projections to release adenosine, which prevents cortical plasticity (i.e., selective expansion of neural representation of behaviorally relevant acoustic stimuli) and perceptual learning (i.e., experience-dependent improvement in frequency discrimination ability). This sound-evoked adenosine release (SEAR) becomes reduced within seconds when acoustic stimuli are tightly paired with the activation of neuromodulatory (cholinergic or dopaminergic) circuits or periods of attentive wakefulness. If thalamic adenosine production is enhanced, then SEAR elevates further, the neuromodulatory circuits are unable to sufficiently reduce SEAR, and associative cortical plasticity and perceptual learning are blocked. This suggests that transient low-adenosine periods triggered by neuromodulatory circuits permit associative cortical plasticity and auditory perceptual learning in adults to occur.

Frequency Specific Optogenetic Stimulation of the Locus Coeruleus Induces Task-Relevant Plasticity in the Motor Cortex

The locus ceruleus (LC) is the primary source of neocortical noradrenaline, which is known to be involved in diverse brain functions including sensory perception, attention, and learning. Previous studies have shown that LC stimulation paired with sensory experience can induce task-dependent plasticity in the sensory neocortex and in the hippocampus. However, it remains unknown whether LC activation similarly impacts neural representations in the agranular motor cortical regions that are responsible for movement planning and production. In this study, we test whether optogenetic stimulation of the LC paired with motor performance is sufficient to induce task-relevant plasticity in the somatotopic cortical motor map. Male and female TH-Cre + rats were trained on a skilled reaching lever-pressing task emphasizing the use of the proximal forelimb musculature, and a viral approach was used to selectively express ChR2 in noradrenergic LC neurons. Once animals reached criterial behavioral performance, they received five training sessions in which correct task performance was paired with optogenetic stimulation of the LC delivered at 3, 10, or 30 Hz. After the last stimulation session, motor cortical mapping was performed using intracortical microstimulation. Our results show that lever pressing paired with LC stimulation at 10 Hz, but not at 3 or 30 Hz, drove the expansion of the motor map representation of the task-relevant proximal FL musculature. These findings demonstrate that phasic, training-paired activation of the LC is sufficient to induce experience-dependent plasticity in the agranular motor cortex and that this LC-driven plasticity is highly dependent on the temporal dynamics of LC activation.

The use of non-invasive brain stimulation in auditory perceptual learning: A review

Auditory perceptual learning is an experience-dependent form of auditory learning that can improve substantially throughout adulthood with practice. A key mechanism associated with perceptual learning is synaptic plasticity. In the last decades, an increasingly better understanding has formed about the neural mechanisms related to auditory perceptual learning. Research in animal models found an association between the functional organization of the primary auditory cortex and frequency discrimination ability. Several studies observed an increase in the area of representation to be associated with improved frequency discrimination. Non-invasive brain stimulation techniques have been related to the promotion of plasticity. Despite its popularity in other fields, non-invasive brain stimulation has not been used much in auditory perceptual learning. The present review has discussed the application of non-invasive brain stimulation methods in auditory perceptual learning by discussing the mechanisms, current evidence and challenges, and future directions.

Precise sound characteristics drive plasticity in the primary auditory cortex with VNS-sound pairing

Introduction

Repeatedly pairing a tone with vagus nerve stimulation (VNS) alters frequency tuning across the auditory pathway. Pairing VNS with speech sounds selectively enhances the primary auditory cortex response to the paired sounds. It is not yet known how altering the speech sounds paired with VNS alters responses. In this study, we test the hypothesis that the sounds that are presented and paired with VNS will influence the neural plasticity observed following VNS-sound pairing.

Methods

To explore the relationship between acoustic experience and neural plasticity, responses were recorded from primary auditory cortex (A1) after VNS was repeatedly paired with the speech sounds 'rad' and 'lad' or paired with only the speech sound 'rad' while 'lad' was an unpaired background sound.

Results

Pairing both sounds with VNS increased the response strength and neural discriminability of the paired sounds in the primary auditory cortex. Surprisingly, pairing only 'rad' with VNS did not alter A1 responses.

Discussion

These results suggest that the specific acoustic contrasts associated with VNS can powerfully shape neural activity in the auditory pathway. Methods to promote plasticity in the central auditory system represent a new therapeutic avenue to treat auditory processing disorders. Understanding how different sound contrasts and neural activity patterns shape plasticity could have important clinical implications.

Frequency-specific modulation of oscillatory activity in the rat auditory cortex by vagus nerve stimulation

BACKGROUND

We previously found that vagus nerve stimulation (VNS) strengthened stimulus-evoked activity in the superficial layer of the sensory cortex but not in the deep layer, suggesting that VNS altered the balance between the feedforward (FF) and feedback (FB) pathways. Band-specific oscillatory activities in the cortex could serve as an index of the FF-FB balance, but whether VNS affects cortical oscillations along sensory pathways through neuromodulators remains unclear.

HYPOTHESIS

VNS modulates the FF-FB balance through the cholinergic and noradrenergic systems, which modulate stimulus gain in the cortex.

METHODS

We investigated the effects of VNS using electrocorticography in the auditory cortex of 34 Wistar rats under general anesthesia while presenting click stimuli. In the time-frequency analyses, the putative modulation of the FF and FB pathways was estimated using high- and low-frequency power. We assessed, using analysis of variance, how VNS modulates auditory-evoked activities and how the modulation changes with cholinergic and noradrenergic antagonists.

RESULTS

VNS increased auditory cortical evoked potentials, consistent with results of our previous work. Furthermore, VNS increased auditory-evoked gamma and beta powers and decreased theta power. Local administration of cholinergic antagonists in the auditory cortex selectively disrupted the VNS-induced increase in gamma and beta power, while noradrenergic antagonists disrupted the decrease in theta power.

CONCLUSIONS

VNS might strengthen the FF pathway through the cholinergic system and attenuate the FB pathway through the noradrenergic system in the auditory cortex. Cortical gain modulation through the VNS-induced neuromodulatory system provides new mechanistic insights into the effect of VNS on auditory processing.

Expression and localization of α2A-adrenergic receptor in the rat post-natal developing cochlea

Lots of adrenergic receptors (ARs) are widely present across the auditory pathways and are positioned to affect auditory and vestibular functions. However, noradrenergic regulation in the cochlea has not been well characterized. In this study, a rat model of noise-induced hearing loss was developed to investigate the expression of α2A-adrenergic receptor (AR) after acoustic trauma, then, we investigated the expression of α2A-AR in the developing rat cochlea using immunofluorescence, qRT-PCR, and Western blotting. We found that the expression of α2A-AR significantly increased in rats exposed to noise compared with controls. Immunofluorescence analysis demonstrated that α2A-AR is localized on hair cells (HCs), spiral ganglion neurons (SGNs), and the stria vascularis (SV) in the postnatal developing cochlea from post-natal day (P) 0 to P28. Furthermore, we observed α2A-AR mRNA reached a maximum level at P14 and P28 when compared with P0, while no significant differences in α2A-AR protein levels at the various stages when compared with P0. This study provides direct evidence for the expression of α2A-AR in HCs, SGNs, and the SV of the cochlea, indicating that norepinephrine might play a vital role in hearing function within the cochlea through α2A-AR.

Effects of transcutaneous auricular vagus nerve stimulation paired with tones on electrophysiological markers of auditory perception

BACKGROUND

Transcutaneous auricular vagus nerve stimulation (taVNS) has been introduced as a non-invasive alternative to invasive vagus nerve stimulation (iVNS). While iVNS paired with tones has been highlighted as a potential effective therapy for the treatment of auditory disorders such as tinnitus, there is still scarce data available confirming the efficacy of non-invasive taVNS. Here, we assessed the effect of taVNS paired with acoustic stimuli on sensory-related electrophysiological responses.

METHODS

A total of 22 healthy participants were investigated with a taVNS tone-pairing paradigm using a within-subjects design. In a single session pure tones paired with either active taVNS or sham taVNS were repeatedly presented. Novel tones without electrical stimulation served as control condition. Auditory event related potentials and auditory cortex oscillations were compared before and after the tone pairing procedure between stimulation conditions.

RESULTS

From pre to post pairing, we observed a decrease in the N1 amplitude and in theta power to tones paired with sham taVNS while these electrophysiological measures remained stable for tones paired with active taVNS a pattern mirroring auditory sensory processing of novel, unpaired control tones.

CONCLUSION

Our results demonstrate the efficacy of a short-term application of non-invasive taVNS to modulate auditory processing in healthy individuals and, thereby, have potential implications for interventions in auditory processing deficits.

Tissue-type plasminogen activator induces conditioned receptive field plasticity in the mouse auditory cortex

Tissue-type plasminogen activator (tPA) is a serine protease that is expressed in various compartments in the brain. It is involved in neuronal plasticity, learning and memory, and addiction. We evaluated whether tPA, exogenously applied, could influence neuroplasticity within the mouse auditory cortex. We used a frequency-pairing paradigm to determine whether neuronal best frequencies shift following the pairing protocol. tPA administration significantly affected the best frequency after pairing, whereby this depended on the pairing frequency relative to the best frequency. When the pairing frequency was above the best frequency, tPA caused a best frequency shift away from the conditioned frequency. tPA significantly widened auditory tuning curves. Our data indicate that regional changes in proteolytic activity within the auditory cortex modulate the fine-tuning of auditory neurons, supporting the function of tPA as a modulator of neuronal plasticity.

State of the art: non-invasive electrical stimulation for the treatment of chronic tinnitus

Subjective tinnitus is the perception of sound in the absence of external stimulation. Neuromodulation is a novel method with promising properties for application in tinnitus management. This study sought to review the types of non-invasive electrical stimulation in tinnitus to provide the foothold for further research. PubMed, EMBASE, and Cochrane databases were searched for studies on the modulation of tinnitus by non-invasive electrical stimulation. Among the four forms of non-invasive electrical modulation, transcranial direct current stimulation, transcranial random noise stimulation, and transauricular vagus nerve stimulation yielded promising results, whereas the effect of transcranial alternating current stimulation in the treatment of tinnitus has not been confirmed. Non-invasive electrical stimulation can effectively suppress tinnitus perception in some patients. However, the heterogeneity in parameter settings leads to scattered and poorly replicated findings. Further high-quality studies are needed to identify optimal parameters to develop more acceptable protocols for tinnitus modulation.

Locus coeruleus activity improves cochlear implant performance

Cochlear implants (CIs) are neuroprosthetic devices that can provide hearing to deaf people1. Despite the benefits offered by CIs, the time taken for hearing to be restored and perceptual accuracy after long-term CI use remain highly variable2,3. CI use is believed to require neuroplasticity in the central auditory system, and differential engagement of neuroplastic mechanisms might contribute to the variability in outcomes4-7. Despite extensive studies on how CIs activate the auditory system4,8-12, the understanding of CI-related neuroplasticity remains limited. One potent factor enabling plasticity is the neuromodulator noradrenaline from the brainstem locus coeruleus (LC). Here we examine behavioural responses and neural activity in LC and auditory cortex of deafened rats fitted with multi-channel CIs. The rats were trained on a reward-based auditory task, and showed considerable individual differences of learning rates and maximum performance. LC photometry predicted when CI subjects began responding to sounds and longer-term perceptual accuracy. Optogenetic LC stimulation produced faster learning and higher long-term accuracy. Auditory cortical responses to CI stimulation reflected behavioural performance, with enhanced responses to rewarded stimuli and decreased distinction between unrewarded stimuli. Adequate engagement of central neuromodulatory systems is thus a potential clinically relevant target for optimizing neuroprosthetic device use.

Locus coeruleus and the defensive activation theory of rapid eye movement sleep: A mechanistic perspective

The defensive activation theory (DAT) was recently proposed to explain the biological function of dreaming. Briefly, DAT states that dreams are primarily visual to prevent plastic take-over of an otherwise inactive visual cortex during sleep. Evidence to support the DAT revolve around the interplay between dream activity (REM%) and cortical plasticity found in evolutionary history, primate studies, and coinciding decline in human cortical plasticity and REM% with age. As the DAT may prove difficult to test experimentally, we investigate whether further support for the DAT can be found in the literature. Plasticity and REM sleep are closely linked to functions of the Locus Coeruleus (LC). We therefore review existing knowledge about the LC covering LC stability with age, and the role of the LC in the plasticity of the visual cortex. Recent studies show the LC to be more stable than previously believed and therefore, the LC likely supports the REM% and plasticity in the same manner throughout life. Based on this finding, we review the effect of aging on REM% and visual cortex plasticity. Here, we find that recent, weighty studies are not in complete agreement with the data originally provided as support for DAT. Results from these studies, however, are not in themselves irreconcilable with the DAT. Our findings therefore do not disprove the DAT. Importantly, we show that the LC is involved in all mechanisms central to the DAT. The LC may therefore provide an experimental window to further explore and test the DAT.

Locus coeruleus ablation in mice: protocol optimization, stereology and behavioral impact

The Locus Coeruleus (LC) is in the brainstem and supplies key brain structures with noradrenaline, including the forebrain and hippocampus. The LC impacts specific behaviors such as anxiety, fear, and motivation, as well as physiological phenomena that impact brain functions in general, including sleep, blood flow regulation, and capillary permeability. Nevertheless, the short- and long-term consequences of LC dysfunction remain unclear. The LC is among the brain structures first affected in patients suffering from neurodegenerative diseases such as Parkinson's disease and Alzheimer's Disease, hinting that LC dysfunction may play a central role in disease development and progression. Animal models with modified or disrupted LC function are essential to further our understanding of LC function in the normal brain, the consequences of LC dysfunction, and its putative roles in disease development. For this, well-characterized animal models of LC dysfunction are needed. Here, we establish the optimal dose of selective neurotoxin N-(2-chloroethyl)-N-ethyl-bromo-benzylamine (DSP-4) for LC ablation. Using histology and stereology, we compare LC volume and neuron number in LC ablated (LCA) mice and controls to assess the efficacy of LC ablation with different numbers of DSP-4 injections. All LCA groups show a consistent decrease in LC cell count and LC volume. We then proceed to characterize the behavior of LCA mice using a light-dark box test, Barnes maze test, and non-invasive sleep-wakefulness monitoring. Behaviorally, LCA mice differ subtly from control mice, with LCA mice generally being more curious and less anxious compared to controls consistent with known LC function and projections. We note an interesting contrast in that control mice have varying LC size and neuron count but consistent behavior whereas LCA mice (as expected) have consistently sized LC but erratic behavior. Our study provides a thorough characterization of an LC ablation model, firmly consolidating it as a valid model system for the study of LC dysfunction.

Topographic and widespread auditory modulation of the somatosensory cortex: potential for bimodal sound and body stimulation for pain treatment

OBJECTIVE

There has been growing interest in understanding multisensory integration in the cortex through activation of multiple sensory and motor pathways to treat brain disorders, such as tinnitus or essential tremors. For tinnitus, previous studies show that combined sound and body stimulation can modulate the auditory pathway and lead to significant improvements in tinnitus symptoms. Considering that tinnitus is a type of chronic auditory pain, bimodal stimulation could potentially alter activity in the somatosensory pathway relevant for treating chronic pain. As an initial step towards that goal, we mapped and characterized neuromodulation effects in the somatosensory cortex (SC) in response to sound and/or electrical stimulation of the body.

APPROACH

We first mapped the topographic organization of activity across the SC of ketamine-anesthetized guinea pigs through electrical stimulation of different body locations using subcutaneous needle electrodes or with broadband acoustic stimulation. We then characterized how neural activity in different parts of the SC could be facilitated or suppressed with bimodal stimulation.

MAIN RESULTS

The topography in the SC of guinea pigs in response to electrical stimulation of the body aligns consistently to that shown in previous rodent studies. Interestingly, auditory broadband noise stimulation primarily excited SC areas that typically respond to stimulation of lower body locations. Although there was only a small subset of SC locations that were excited by acoustic stimulation alone, all SC recording sites could be altered (facilitated or suppressed) with bimodal stimulation. Furthermore, specific regions of the SC could be modulated by stimulating an appropriate body region combined with broadband noise.

SIGNIFICANCE

These findings show that bimodal stimulation can excite or modulate firing across a widespread yet targeted population of SC neurons. This approach may provide a non-invasive method for altering or disrupting abnormal firing patterns within certain parts of the SC for chronic pain treatment.

Current challenges in reliably targeting the noradrenergic locus coeruleus using transcutaneous auricular vagus nerve stimulation (taVNS)

Transcutaneous auricular vagus nerve stimulation (taVNS), as a non-invasive brain stimulation technique may influence the locus coeruleus-norepinephrine system (LC-NE system) via modulation of the Vagus Nerve (VN) which projects to the LC. Few human studies exist examining the effects of taVNS on the LC-NE system and studies to date assessing the ability of taVNS to target the LC yield heterogeneous results. The aim of this review is to present an overview of the current challenges in assessing effects of taVNS on LC function and how translational approaches spanning animal and human research can help in this regard. A particular emphasis of the review discusses how the effects of taVNS may be influenced by changes in structure and function of the LC-NE system across the human lifespan and in disease.

Learning-induced plasticity in the barrel cortex is disrupted by inhibition of layer 4 somatostatin-containing interneurons

Gaba-ergic neurons are a diverse cell class with extensive influence over cortical processing, but their role in experience-dependent plasticity is not completely understood. Here we addressed the role of cortical somatostatin- (SOM-INs) and vasoactive intestinal polypeptide- (VIP-INs) containing interneurons in a Pavlovian conditioning where stimulation of the vibrissae is used as a conditioned stimulus and tail shock as unconditioned one. This procedure induces a plastic change observed as an enlargement of the cortical functional representation of vibrissae activated during conditioning. Using layer-targeted, cell-selective DREADD transductions, we examined the involvement of SOM-INs and VIP-INs activity in learning-related plastic changes. Under optical recordings, we injected DREADD-expressing vectors into layer IV (L4) barrels or layer II/III (L2/3) areas corresponding to the activated vibrissae. The activity of the interneurons was modulated during all conditioning sessions, and functional 2-deoxyglucose (2DG) maps were obtained 24 h after the last session. In mice with L4 but not L2/3 SOM-INs suppressed during conditioning, the plastic change of whisker representation was absent. The behavioral effect of conditioning was disturbed. Both L4 SOM-INs excitation and L2/3 VIP-INs inhibition during conditioning did not affect the plasticity or the conditioned response. We found the activity of L4 SOM-INs is indispensable in the formation of learning-induced plastic change. We propose that L4 SOM-INs may provide disinhibition by blocking L4 parvalbumin interneurons, allowing a flow of information into upper cortical layers during learning.

When and How Does the Auditory Cortex Influence Subcortical Auditory Structures? New Insights About the Roles of Descending Cortical Projections

For decades, the corticofugal descending projections have been anatomically well described but their functional role remains a puzzling question. In this review, we will first describe the contributions of neuronal networks in representing communication sounds in various types of degraded acoustic conditions from the cochlear nucleus to the primary and secondary auditory cortex. In such situations, the discrimination abilities of collicular and thalamic neurons are clearly better than those of cortical neurons although the latter remain very little affected by degraded acoustic conditions. Second, we will report the functional effects resulting from activating or inactivating corticofugal projections on functional properties of subcortical neurons. In general, modest effects have been observed in anesthetized and in awake, passively listening, animals. In contrast, in behavioral tasks including challenging conditions, behavioral performance was severely reduced by removing or transiently silencing the corticofugal descending projections. This suggests that the discriminative abilities of subcortical neurons may be sufficient in many acoustic situations. It is only in particularly challenging situations, either due to the task difficulties and/or to the degraded acoustic conditions that the corticofugal descending connections bring additional abilities. Here, we propose that it is both the top-down influences from the prefrontal cortex, and those from the neuromodulatory systems, which allow the cortical descending projections to impact behavioral performance in reshaping the functional circuitry of subcortical structures. We aim at proposing potential scenarios to explain how, and under which circumstances, these projections impact on subcortical processing and on behavioral responses.

Sympathetic Nervous System Regulation of Auditory Function

BACKGROUND

The auditory system processes how we hear and understand sounds within the environment. It comprises both peripheral and central structures. Sympathetic nervous system projections are present throughout the auditory system. The function of sympathetic fibers in the cochlea has not been studied extensively due to the limited number of direct projections in the auditory system. Nevertheless, research on adrenergic and noradrenergic regulation of the cochlea and central auditory system is growing. With the rapid development of neuroscience, auditory central regulation is an extant topic of focus in research on hearing.

SUMMARY

As such, understanding sympathetic nervous system regulation of auditory function is a growing topic of interest. Herein, we review the distribution and putative physiological and pathological roles of sympathetic nervous system projections in hearing. Key Messages: In the peripheral auditory system, the sympathetic nervous system regulates cochlear blood flow, modulates cochlear efferent fibers, affects hair cells, and influences the habenula region. In central auditory pathways, norepinephrine is essential for plasticity in the auditory cortex and affects auditory cortex activity. In pathological states, the sympathetic nervous system is associated with many hearing disorders. The mechanisms and pathways of sympathetic nervous system modulation of auditory function is still valuable for us to research and discuss.

Short-Term Effects of Vagus Nerve Stimulation on Learning and Evoked Activity in Auditory Cortex

Chronic vagus nerve stimulation (VNS) has been shown to facilitate learning, but effects of acute VNS on neural coding and behavior remain less well understood. Ferrets implanted with cuff electrodes on the vagus nerve were trained by classical conditioning on an auditory tone frequency-reward association. One tone was associated with reward while another tone was not. Tone frequencies and reward associations were changed every 2 d, requiring learning of a new relationship. When tones were paired with VNS, animals consistently learned the new association within 2 d. When VNS occurred randomly between trials, learning within 2 d was unreliable. In passively listening animals, neural activity in primary auditory cortex (A1) and pupil size were recorded before and after acute VNS-tone pairing. After pairing with a neuron’s best-frequency (BF) tone, responses by a subpopulation of neurons were reduced. VNS paired with an off-BF tone or during intertrial intervals had no effect. The BF-specific reduction in neural responses after VNS remained, even after regressing out changes explained by pupil-indexed arousal. VNS induced brief dilation in the pupil, and the size of this change predicted the magnitude of persistent changes in the neural response. This interaction suggests that fluctuations in neuromodulation associated with arousal gate the long-term VNS effects on neural activity.

Emotional Arousal and Valence Jointly Modulate the Auditory Response: A 40-Hz ASSR Study

Emotion is defined as a response to external stimuli and internal mental representations. It has been characterized as a multidimensional concept, primarily comprising two dimensions: valence and arousal. Existing studies have demonstrated that emotional experience exerts a powerful impact on auditory processing in terms of valence. However, it has also been shown that while negative emotion can improve auditory perception in healthy subjects, patients with depression show deficits in auditory perception. We thus speculated that both arousal and valence jointly modulate auditory perception. To examine the emotion-driven effects on the auditory response, we induced positive, negative, and neutral emotional states in healthy subjects and collected auditory steady-state response (ASSR) evoked by a 40-Hz chirp sound. We calculated peak-to-peak amplitude (PPA) and event-related spectral perturbation (ERSP) of evoked ASSRs and observed that the positive emotions significantly enhanced brain responses to auditory stimuli (p < 0.001), but that ASSRs in a negative state were not significantly enhanced compared with the neutral state. Subsequently, regression analysis showed a significant positive multiple linear relationship between the PPA and ratings of two emotional dimensions, indicating that arousal and valence jointly regulated the auditory cortex's synchronous oscillation, rather than the valence in isolation, offering the potential to clarify the conflicting results surrounding the role of negative emotions in auditory responses. Because depression is generally characterized by low arousal and low valence in actual life, whereas the negative emotion evoked under laboratory conditions is always with low valence but high arousal.

Phasic activation of the locus coeruleus attenuates the acoustic startle response by increasing cortical arousal

An alerting sound elicits the Acoustic Startle Response (ASR) that is dependent on the sound volume and organisms’ state, which is regulated by neuromodulatory centers. The locus coeruleus (LC) neurons respond to salient stimuli and noradrenaline release affects sensory processing, including auditory. The LC hyperactivity is detrimental for sensorimotor gating. We report here that priming microstimulation of the LC (100-ms at 20, 50, and 100 Hz) attenuated the ASR in rats. The ASR reduction scaled with frequency and 100 Hz-stimulation mimicked pre-exposure to a non-startling tone (prepulse). A rapid (~ 40 ms) EEG desynchronization following the LC stimulation suggested that the ASR reduction was due to elevated cortical arousal. The effects of LC stimulation on the ASR and EEG were consistent with systematic relationships between the ASR, awake/sleep state, and the cortical arousal level; for that matter, a lower ASR amplitude corresponded to a higher arousal level. Thus, the LC appears to modulate the ASR circuit via its diffuse ascending projections to the forebrain saliency network. The LC modulation directly in the brainstem and/or spinal cord may also play a role. Our findings suggest the LC as a part of the brain circuitry regulating the ASR, while underlying neurophysiological mechanisms require further investigation.

Bimodal Auditory Electrical Stimulation for the Treatment of Tinnitus: Preclinical and Clinical Studies

Tinnitus, or the phantom perception of sound, arises from pathological neural activity. Neurophysiological research has shown increased spontaneous firing rates and synchronization along the auditory pathway correlate strongly with behavioral measures of tinnitus. Auditory neurons are plastic, enabling external stimuli to be utilized to elicit long-term changes to spontaneous firing and synchrony. Pathological plasticity can thus be reversed using bimodal auditory plus nonauditory stimulation to reduce tinnitus. This chapter discusses preclinical and clinical evidence for efficacy of bimodal stimulation treatments of tinnitus, with highlights on sham-controlled, double-blinded clinical trials. The results from these studies have shown some efficacy in reducing the severity of tinnitus, based on subjective and objective outcome measures including tinnitus questionnaires and psychophysical tinnitus measurements. While results of some studies have been positive, the degree of benefit and the populations that respond to treatment vary across the studies. Directions and implications of future studies are discussed.

Enhanced Discriminative Abilities of Auditory Cortex Neurons for Pup Calls Despite Reduced Evoked Responses in C57BL/6 Mother Mice

A fundamental task for the auditory system is to process communication sounds according to their behavioral significance. In many mammalian species, pup calls became more significant for mothers than other conspecific and heterospecific communication sounds. To study the cortical consequences of motherhood on the processing of communication sounds, we recorded neuronal responses in the primary auditory cortex of virgin and mother C57BL/6 mice which had similar ABR thresholds. In mothers, the evoked firing rate in response to pure tones was decreased and the frequency receptive fields were narrower. The responses to pup and adult calls were also reduced but the amount of mutual information (MI) per spike about the pup call's identity was increased in mother mice. The response latency to pup and adult calls was significantly shorter in mothers. Despite similarly decreased responses to guinea pig whistles, the response latency, and the MI per spike did not differ between virgins and mothers for these heterospecific vocalizations. Noise correlations between cortical recordings were decreased in mothers, suggesting that the firing rate of distant neurons was more independent from each other. Together, these results indicate that in the most commonly used mouse strain for behavioral studies, the discrimination of pup calls by auditory cortex neurons is more efficient during motherhood.

Distribution and co-expression of adrenergic receptor-encoding mRNA in the mouse inferior colliculus

Adrenergic receptors are mediators of adrenergic and noradrenergic modulation throughout the brain. Previous studies have provided evidence for the expression of adrenergic receptors in the midbrain auditory nucleus, the inferior colliculus (IC), but have not examined the cellular patterns of expression in detail. Here, we utilize multichannel fluorescent in situ hybridization to detect the expression of adrenergic receptor-encoding mRNA in the inferior colliculus of male and female mice. We found expression of α₁ , α_2A , and β₂ receptor-encoding mRNA throughout all areas of the IC. While we observed similar levels of expression of α₁ receptor-encoding mRNA across the subregions of the IC, α_2A and β₂ receptor-encoding mRNA was expressed differentially. To account for developmental changes in noradrenergic receptor expression, we measured expression levels in mice aged P15, P20, and P60. We observed little change in levels of expression across these ages. To ascertain the modulatory potential of multiple adrenergic receptor subtypes in a single IC cell, we measured co-expression of α₁ , α_2A , and β₂ receptor-encoding mRNA. We found greater proportions of cells in the IC that expressed no adrenergic receptor-encoding mRNA, α1 and α2A adrenergic receptor-encoding mRNA, and α1, α2A, and β2 receptor-encoding mRNA than would be predicted by independent expression of each receptor subtype. These data suggest a coordinated pattern of adrenergic receptor expression in the IC and provide the first evidence for adrenergic receptor expression and co-expression in the subregions of the mouse auditory midbrain.

Vagus nerve stimulation (VNS)-induced layer-specific modulation of evoked responses in the sensory cortex of rats

Neuromodulation achieved by vagus nerve stimulation (VNS) induces various neuropsychiatric effects whose underlying mechanisms of action remain poorly understood. Innervation of neuromodulators and a microcircuit structure in the cerebral cortex informed the hypothesis that VNS exerts layer-specific modulation in the sensory cortex and alters the balance between feedforward and feedback pathways. To test this hypothesis, we characterized laminar profiles of auditory-evoked potentials (AEPs) in the primary auditory cortex (A1) of anesthetized rats with an array of microelectrodes and investigated the effects of VNS on AEPs and stimulus specific adaptation (SSA). VNS predominantly increased the amplitudes of AEPs in superficial layers, but this effect diminished with depth. In addition, VNS exerted a stronger modulation of the neural responses to repeated stimuli than to deviant stimuli, resulting in decreased SSA across all layers of the A1. These results may provide new insights that the VNS-induced neuropsychiatric effects may be attributable to a sensory gain mechanism: VNS strengthens the ascending input in the sensory cortex and creates an imbalance in the strength of activities between superficial and deep cortical layers, where the feedfoward and feedback pathways predominantly originate, respectively.

Dopamine and Noradrenaline in the Brain; Overlapping or Dissociate Functions?

Dopamine and noradrenaline are crucial neuromodulators controlling brain states, vigilance, action, reward, learning, and memory processes. Ventral tegmental area (VTA) and Locus Coeruleus (LC) are canonically described as the main sources of dopamine (DA) and noradrenaline (NA) with dissociate functions. A comparison of diverse studies shows that these neuromodulators largely overlap in multiple domains such as shared biosynthetic pathway and co-release from the LC terminals, convergent innervations, non-specificity of receptors and transporters, and shared intracellular signaling pathways. DA–NA interactions are mainly studied in prefrontal cortex and hippocampus, yet it can be extended to the whole brain given the diversity of catecholamine innervations. LC can simultaneously broadcast both dopamine and noradrenaline across the brain. Here, we briefly review the molecular, cellular, and physiological overlaps between DA and NA systems and point to their functional implications. We suggest that DA and NA may function in parallel to facilitate learning and maintain the states required for normal cognitive processes. Various signaling modules of NA and DA have been targeted for developing of therapeutics. Understanding overlaps of the two systems is crucial for more effective interventions in a range of neuropsychiatric conditions.

Sleep Spindles: Mechanisms and Functions

Sleep spindles are burstlike signals in the electroencephalogram (EEG) of the sleeping mammalian brain and electrical surface correlates of neuronal oscillations in thalamus. As one of the most inheritable sleep EEG signatures, sleep spindles probably reflect the strength and malleability of thalamocortical circuits that underlie individual cognitive profiles. We review the characteristics, organization, regulation, and origins of sleep spindles and their implication in non-rapid-eye-movement sleep (NREMS) and its functions, focusing on human and rodent. Spatially, sleep spindle-related neuronal activity appears on scales ranging from small thalamic circuits to functional cortical areas, and generates a cortical state favoring intracortical plasticity while limiting cortical output. Temporally, sleep spindles are discrete events, part of a continuous power band, and elements grouped on an infraslow time scale over which NREMS alternates between continuity and fragility. We synthesize diverse and seemingly unlinked functions of sleep spindles for sleep architecture, sensory processing, synaptic plasticity, memory formation, and cognitive abilities into a unifying sleep spindle concept, according to which sleep spindles 1) generate neural conditions of large-scale functional connectivity and plasticity that outlast their appearance as discrete EEG events, 2) appear preferentially in thalamic circuits engaged in learning and attention-based experience during wakefulness, and 3) enable a selective reactivation and routing of wake-instated neuronal traces between brain areas such as hippocampus and cortex. Their fine spatiotemporal organization reflects NREMS as a physiological state coordinated over brain and body and may indicate, if not anticipate and ultimately differentiate, pathologies in sleep and neurodevelopmental, -degenerative, and -psychiatric conditions.

Redefining Noradrenergic Neuromodulation of Behavior: Impacts of a Modular Locus Coeruleus Architecture

The locus coeruleus (LC) is a seemingly singular and compact neuromodulatory nucleus that is a prominent component of disparate theories of brain function due to its broad noradrenergic projections throughout the CNS. As a diffuse neuromodulatory system, noradrenaline affects learning and decision making, control of sleep and wakefulness, sensory salience including pain, and the physiology of correlated forebrain activity (ensembles and networks) and brain hemodynamic responses. However, our understanding of the LC is undergoing a dramatic shift due to the application of state-of-the-art methods that reveal a nucleus of many modules that provide targeted neuromodulation. Here, we review the evidence supporting a modular LC based on multiple levels of observation (developmental, genetic, molecular, anatomical, and neurophysiological). We suggest that the concept of the LC as a singular nucleus and, alongside it, the role of the LC in diverse theories of brain function must be reconsidered.

Locus coeruleus-norepinephrine modulation of sensory processing and perception: A focused review

The locus coeruleus-norepinephrine (LC-NE) system is involved in many brain functions and neurological disorders. In this review we discuss how LC-NE signaling affects the activity of cortical and subcortical sensory neurons, and how it influences perception-driven behaviors associated with mammalian somatosensory, visual, auditory, and olfactory systems. We summarize the consistent as well as seemingly inconsistent findings across brain areas and sensory modalities and propose a framework to understand these phenomena from the perspective of adrenergic receptor expression, dose-dependent physiology and excitation-inhibition balance. We also discuss potential future research directions in this field.

β-adrenergic modulation of discrimination learning and memory in the auditory cortex

Despite vast literature on catecholaminergic neuromodulation of auditory cortex functioning in general, knowledge about its role for long‐term memory formation is scarce. Our previous pharmacological studies on cortex‐dependent frequency‐modulated tone‐sweep discrimination learning of Mongolian gerbils showed that auditory‐cortical D_1/5‐dopamine receptor activity facilitates memory consolidation and anterograde memory formation. Considering overlapping functions of D_1/5‐dopamine receptors and β‐adrenoceptors, we hypothesised a role of β‐adrenergic signalling in the auditory cortex for sweep discrimination learning and memory. Supporting this hypothesis, the β_1/2‐adrenoceptor antagonist propranolol bilaterally applied to the gerbil auditory cortex after task acquisition prevented the discrimination increment that was normally monitored 1 day later. The increment in the total number of hurdle crossings performed in response to the sweeps per se was normal. Propranolol infusion after the seventh training session suppressed the previously established sweep discrimination. The suppressive effect required antagonist injection in a narrow post‐session time window. When applied to the auditory cortex 1 day before initial conditioning, β₁‐adrenoceptor‐antagonising and β₁‐adrenoceptor‐stimulating agents retarded and facilitated, respectively, sweep discrimination learning, whereas β₂‐selective drugs were ineffective. In contrast, single‐sweep detection learning was normal after propranolol infusion. By immunohistochemistry, β₁‐ and β₂‐adrenoceptors were identified on the neuropil and somata of pyramidal and non‐pyramidal neurons of the gerbil auditory cortex. The present findings suggest that β‐adrenergic signalling in the auditory cortex has task‐related importance for discrimination learning of complex sounds: as previously shown for D_1/5‐dopamine receptor signalling, β‐adrenoceptor activity supports long‐term memory consolidation and reconsolidation; additionally, tonic input through β₁‐adrenoceptors may control mechanisms permissive for memory acquisition.

Pairing vagus nerve stimulation with tones drives plasticity across the auditory pathway

Previous studies have demonstrated that pairing vagus nerve stimulation (VNS) with sounds can enhance the primary auditory cortex (A1) response to the paired sound. The neural response to sounds following VNS-sound pairing in other subcortical and cortical auditory fields has not been documented. We predicted that VNS-tone pairing would increase neural responses to the paired tone frequency across the auditory pathway. In this study, we paired VNS with the presentation of a 9-kHz tone 300 times a day for 20 days. We recorded neural responses to tones from 2,950 sites in the inferior colliculus (IC), A1, anterior auditory field (AAF), and posterior auditory field (PAF) 24 h after the last pairing session in anesthetized rats. We found that VNS-tone pairing increased the percentage of IC, A1, AAF, and PAF that responds to the paired tone frequency. Across all tested auditory fields, the response strength to tones was strengthened in VNS-tone paired rats compared with control rats. VNS-tone pairing reduced spontaneous activity, frequency selectivity, and response threshold across the auditory pathway. This is the first study to document both cortical and subcortical plasticity following VNS-sound pairing. Our findings suggest that VNS paired with sound presentation is an effective method to enhance auditory processing.NEW & NOTEWORTHY Previous studies have reported primary auditory cortex plasticity following vagus nerve stimulation (VNS) paired with a sound. This study extends previous findings by documenting that fields across the auditory pathway are altered by VNS-tone pairing. VNS-tone pairing increases the percentage of each field that responds to the paired tone frequency. This is the first study to document both cortical and subcortical plasticity following VNS-sound pairing.

Capacities and neural mechanisms for auditory statistical learning across species

Statistical learning has been proposed as a possible mechanism by which individuals can become sensitive to the structures of language fundamental for speech perception. Since its description in human infants, statistical learning has been described in human adults and several non-human species as a general process by which animals learn about stimulus-relevant statistics. The neurobiology of statistical learning is beginning to be understood, but many questions remain about the underlying mechanisms. Why is the developing brain particularly sensitive to stimulus and environmental statistics, and what neural processes are engaged in the adult brain to enable learning from statistical regularities in the absence of external reward or instruction? This review will survey the statistical learning abilities of humans and non-human animals with a particular focus on communicative vocalizations. We discuss the neurobiological basis of statistical learning, and specifically what can be learned by exploring this process in both humans and laboratory animals. Finally, we describe advantages of studying vocal communication in rodents as a means to further our understanding of the cortical plasticity mechanisms engaged during statistical learning. We examine the use of rodents in the context of pup retrieval, which is an auditory-based and experience-dependent form of maternal behavior.

Cortical map plasticity as a function of vagus nerve stimulation rate

BACKGROUND

Repeatedly pairing a brief train of vagus nerve stimulation (VNS) with an external event can reorganize the sensory or motor cortex. A 30 Hz train of sixteen VNS pulses paired with a tone significantly increases the number of neurons in primary auditory cortex (A1) that respond to tones near the paired tone frequency. The effective range of VNS pulse rates for driving cortical map plasticity has not been defined.

OBJECTIVE/HYPOTHESIS

This project investigated the effects of VNS rate on cortical plasticity. We expected that VNS pulse rate would affect the degree of plasticity caused by VNS-tone pairing.

METHODS

Rats received sixteen pulses of VNS delivered at a low (7.5 Hz), moderate (30 Hz), or high (120 Hz) rate paired with 9 kHz tones 300 times per day over a 20 day period.

RESULTS

More A1 neurons responded to the paired tone frequency in rats from the moderate rate VNS group compared to naïve controls. The response strength was also increased in these rats. In contrast, rats that received high or low rate VNS failed to exhibit a significant increase in the number of neurons tuned to sounds near 9 kHz.

CONCLUSION

Our results demonstrate that the degree of cortical plasticity caused by VNS-tone pairing is an inverted-U function of VNS pulse rate. The apparent high temporal precision of VNS-tone pairing helps identify optimal VNS parameters to achieve the beneficial effects from restoration of sensory or motor function.

Varying Stimulation Parameters to Improve Cortical Plasticity Generated by VNS-tone Pairing

Pairing vagus nerve stimulation (VNS) with movements or sounds can direct robust plasticity in motor or auditory cortex, respectively. The degree of map plasticity is influenced by the intensity and pulse width of VNS, number of VNS-event pairings, and the interval between each pairing. It is likely that these parameters interact, influencing optimal implementation of VNS pairing protocols. We varied VNS intensity, number of stimulations, and inter-stimulation interval (ISI) to test for interactions among these parameters. Rats were implanted with a vagus nerve stimulating cuff and randomly assigned to one of three treatment groups to receive 20 days of VNS paired with a 9-kHz tone: (1) Fast VNS: 50 daily pairings of 400-µA VNS with a 30-s ISI; (2) Dispersed VNS: 50 daily pairings of 400-µA VNS with a 180-s ISI; and (3) Standard VNS: 300 daily pairings of 800-µA VNS with a 30-s ISI. Following 20 days of VNS-tone pairing, multi-unit recordings were conducted in primary auditory cortex (A1) and receptive field properties were analyzed. Increasing ISI (Dispersed VNS) did not lead to an enhancement of cortical plasticity. Reducing the current intensity and number of stimulations (Fast VNS) resulted in robust cortical plasticity, using 6 times fewer VNS pairings than the Standard protocol. These findings reveal an interaction between current intensity, stimulation number, and ISI and identify a novel VNS paradigm that is substantially more efficient than the previous standard paradigm.

Familiarity with social sounds alters c-Fos expression in auditory cortex and interacts with estradiol in locus coeruleus

When a social sound category initially gains behavioral significance to an animal, plasticity events presumably enhance the ability to recognize that sound category in the future. In the context of learning natural social stimuli, neuromodulators such as norepinephrine and estrogen have been associated with experience-dependent plasticity and processing of newly salient social cues, yet continued plasticity once stimuli are familiar could disrupt the stability of sensorineural representations. Here we employed a maternal mouse model of natural sensory cortical plasticity for infant vocalizations to ask whether the engagement of the noradrenergic locus coeruleus (LC) by the playback of pup-calls is affected by either prior experience with the sounds or estrogen availability, using a well-studied cellular activity and plasticity marker, the immediate early gene c-Fos. We counted call-induced c-Fos immunoreactive (cFos-IR) cells in both LC and physiologically validated fields within the auditory cortex (AC) of estradiol or blank-implanted virgin female mice with either 0 or 5-days prior experience caring for vocalizing pups. Estradiol and pup experience interacted both in the induction of c-Fos-IR in the LC, as well as in behavioral measures of locomotion during playback, consistent with the neuromodulatory center’s activity being an online reflection of both hormonal and experience-dependent influences on arousal. Throughout core AC, as well as in a high frequency sub-region of AC and in secondary AC, a main effect of pup experience was to reduce call-induced c-Fos-IR, irrespective of estradiol availability. This is consistent with the hypothesis that sound familiarity leads to less c-Fos-mediated plasticity, and less disrupted sensory representations of a meaningful call category. Taken together, our data support the view that any coupling between these sensory and neuromodulatory areas is situationally dependent, and their engagement depends differentially on both internal state factors like hormones and external state factors like prior experience.

Locus coeruleus activation accelerates perceptual learning

Neural representations of the external world are constructed and updated in a manner that depends on behavioral context. For neocortical networks, this contextual information is relayed by a diverse range of neuromodulatory systems, which govern attention and signal the value of internal state variables such as arousal, motivation, and stress. Neuromodulators enable cortical circuits to differentially process specific stimuli and modify synaptic strengths in order to maintain short- or long-term memory traces of significant perceptual events and behavioral episodes. One of the most important subcortical neuromodulatory systems for attention and arousal is the noradrenergic locus coeruleus. Here we report that the noradrenergic system can enhance behavior in rats performing a self-initiated auditory recognition task, and optogenetic stimulation of noradrenergic locus coeruleus neurons accelerated the rate at which trained rats began correctly responding to a change in reward contingency. Animals successively progressed through distinct behavioral epochs, including periods of perseverance and exploration that occurred much more rapidly when animals received locus coeruleus stimulation. In parallel, we made recordings from primary auditory cortex and found that pairing tones with locus coeruleus stimulation led to a similar set of changes to cortical tuning profiles. Thus both behavioral and neural responses go through phases of adjustment for exploring and exploiting environmental reward contingencies. Furthermore, behavioral engagement does not necessarily recruit optimal locus coeruleus activity.

The Sensory Neocortex and Associative Memory

Most behaviors in mammals are directly or indirectly guided by prior experience and therefore depend on the ability of our brains to form memories. The ability to form an association between an initially possibly neutral sensory stimulus and its behavioral relevance is essential for our ability to navigate in a changing environment. The formation of a memory is a complex process involving many areas of the brain. In this chapter we review classic and recent work that has shed light on the specific contribution of sensory cortical areas to the formation of associative memories. We discuss synaptic and circuit mechanisms that mediate plastic adaptations of functional properties in individual neurons as well as larger neuronal populations forming topographically organized representations. Furthermore, we describe commonly used behavioral paradigms that are used to study the mechanisms of memory formation. We focus on the auditory modality that is receiving increasing attention for the study of associative memory in rodent model systems. We argue that sensory cortical areas may play an important role for the memory-dependent categorical recognition of previously encountered sensory stimuli.

Inconsistent Effect of Arousal on Early Auditory Perception

Mood has been shown to influence cognitive performance. However, little is known about the influence of mood on sensory processing, specifically in the auditory domain. With the current study, we sought to investigate how auditory processing of neutral sounds is affected by the mood state of the listener. This was tested in two experiments by measuring masked-auditory detection thresholds before and after a standard mood-induction procedure. In the first experiment (N = 76), mood was induced by imagining a mood-appropriate event combined with listening to mood inducing music. In the second experiment (N = 80), imagining was combined with affective picture viewing to exclude any possibility of confounding the results by acoustic properties of the music. In both experiments, the thresholds were determined by means of an adaptive staircase tracking method in a two-interval forced-choice task. Masked detection thresholds were compared between participants in four different moods (calm, happy, sad, and anxious), which enabled differentiation of mood effects along the dimensions arousal and pleasure. Results of the two experiments were analyzed both in separate analyses and in a combined analysis. The first experiment showed that, while there was no impact of pleasure level on the masked threshold, lower arousal was associated with lower threshold (higher masked sensitivity). However, as indicated by an interaction effect between experiment and arousal, arousal did have a different effect on the threshold in Experiment 2. Experiment 2 showed a trend of arousal in opposite direction. These results show that the effect of arousal on auditory-masked sensitivity may depend on the modality of the mood-inducing stimuli. As clear conclusions regarding the genuineness of the arousal effect on the masked threshold cannot be drawn, suggestions for further research that could clarify this issue are provided.

lncRNA expression in the auditory forebrain during postnatal development

The biological processes governing brain development and maturation depend on complex patterns of gene and protein expression, which can be influenced by many factors. One of the most overlooked is the long noncoding class of RNAs (lncRNAs), which are known to play important regulatory roles in an array of biological processes. Little is known about the distribution of lncRNAs in the sensory systems of the brain, and how lncRNAs interact with other mechanisms to guide the development of these systems. In this study, we profiled lncRNA expression in the mouse auditory forebrain during postnatal development at time points before and after the onset of hearing (P7, P14, P21, adult). First, we generated lncRNA profiles of the primary auditory cortex (A1) and medial geniculate body (MG) at each age. Then, we determined the differential patterns of expression by brain region and age. These analyses revealed that the lncRNA expression profile was distinct between both brain regions and between each postnatal age, indicating spatial and temporal specificity during maturation of the auditory forebrain. Next, we explored potential interactions between functionally-related lncRNAs, protein coding RNAs (pcRNAs), and associated proteins. The maturational trajectories (P7 to adult) of many lncRNA - pcRNA pairs were highly correlated, and predictive analyses revealed that lncRNA-protein interactions tended to be strong. A user-friendly database was constructed to facilitate inspection of the expression levels and maturational trajectories for any lncRNA or pcRNA in the database. Overall, this study provides an in-depth summary of lncRNA expression in the developing auditory forebrain and a broad-based foundation for future exploration of lncRNA function during brain development.

Layer- and area-specific actions of norepinephrine on cortical synaptic transmission

The cerebral cortex is a critical target of the central noradrenergic system. The importance of norepinephrine (NE) in the regulation of cortical activity is underscored by clinical findings that involve this catecholamine and its receptor subtypes in the regulation of a large number of emotional and cognitive functions and illnesses. In this review, we highlight diverse effects of the LC/NE system in the mammalian cortex. Indeed, electrophysiological, pharmacological, and behavioral studies in the last few decades reveal that NE elicits a mixed repertoire of excitatory, inhibitory, and biphasic effects on the firing activity and transmitter release of cortical neurons. At the intrinsic cellular level, NE can produce a series of effects similar to those elicited by other monoamines or acetylcholine, associated with systemic arousal. At the synaptic level, NE induces numerous acute changes in synaptic function, and ׳gates' the induction of long-term plasticity of glutamatergic synapses, consisting in an enhancement of engaged and relevant cortical synapses and/or depression of unengaged synapses. Equally important in shaping cortical function, in many cortical areas NE promotes a characteristic, most often reversible, increase in the gain of local inhibitory synapses, whose extent and temporal properties vary between different areas and sometimes even between cortical layers of the same area. While we are still a long way from a comprehensive theory of the function of the LC/NE system, its cellular, synaptic, and plastic effects are consistent with the hypothesis that noradrenergic modulation is critical in coordinating the activity of cortical and subcortical circuits for the integration of sensory activity and working memory. This article is part of a Special Issue entitled SI: Noradrenergic System.

Neuroanatomical Evidence for Catecholamines as Modulators of Audition and Acoustic Behavior in a Vocal Teleost

The plainfin midshipman fish (Porichthys notatus) is a well-studied model to understand the neural and endocrine mechanisms underlying vocal-acoustic communication across vertebrates. It is well established that steroid hormones such as estrogen drive seasonal peripheral auditory plasticity in female Porichthys in order to better encode the male's advertisement call. However, little is known of the neural substrates that underlie the motivation and coordinated behavioral response to auditory social signals. Catecholamines, which include dopamine and noradrenaline, are good candidates for this function, as they are thought to modulate the salience of and reinforce appropriate behavior to socially relevant stimuli. This chapter summarizes our recent studies which aimed to characterize catecholamine innervation in the central and peripheral auditory system of Porichthys as well as test the hypotheses that innervation of the auditory system is seasonally plastic and catecholaminergic neurons are activated in response to conspecific vocalizations. Of particular significance is the discovery of direct dopaminergic innervation of the saccule, the main hearing end organ, by neurons in the diencephalon, which also robustly innervate the cholinergic auditory efferent nucleus in the hindbrain. Seasonal changes in dopamine innervation in both these areas appear dependent on reproductive state in females and may ultimately function to modulate the sensitivity of the peripheral auditory system as an adaptation to the seasonally changing soundscape. Diencephalic dopaminergic neurons are indeed active in response to exposure to midshipman vocalizations and are in a perfect position to integrate the detection and appropriate motor response to conspecific acoustic signals for successful reproduction.

Are there “local hotspots?” When concepts of cognitive psychology do not fit with physiological results

Mather and colleagues' arguments require rethinking at the mechanistic level. The arguments on the physiological effects of norepinephrine at the cortical level are inconsistent with large parts of the literature. There is no evidence that norepinephrine induces local “hotspots”: Norepinephrine mainly decreases evoked responses; facilitating effects are rare and not localized. More generally, the idea that perception benefits from “local hotspots” is hardly compatible with the fact that neural representations involve largely distributed activation of cortical and subcortical networks.

Neuromodulatory influence of norepinephrine during developmental experience-dependent plasticity

Critical periods represent phases of development during which neuronal circuits and their responses can be readily shaped by stimuli. Experience-dependent plasticity that occurs within these critical periods can be influenced in many ways; however, Shepard et al. (J Neurosci 35: 2432-2437, 2015) recently singled out norepinephrine as an essential driver of this plasticity within the auditory cortex. This work provides novel insight into the mechanisms of critical period plasticity and challenges previous conceptions that a functional redundancy exists between noradrenergic and cholinergic influences on cortical plasticity.

Unraveling the Biology of Auditory Learning: A Cognitive-Sensorimotor-Reward Framework

The auditory system is stunning in its capacity for change: a single neuron can modulate its tuning in minutes. Here we articulate a conceptual framework to understand the biology of auditory learning where an animal must engage cognitive, sensorimotor, and reward systems to spark neural remodeling. Central to our framework is a consideration of the auditory system as an integrated whole that interacts with other circuits to guide and refine life in sound. Despite our emphasis on the auditory system, these principles may apply across the nervous system. Understanding neuroplastic changes in both normal and impaired sensory systems guides strategies to improve everyday communication.

Learning strategy refinement reverses early sensory cortical map expansion but not behavior: Support for a theory of directed cortical substrates of learning and memory

Primary sensory cortical fields develop highly specific associative representational plasticity, notably enlarged area of representation of reinforced signal stimuli within their topographic maps. However, overtraining subjects after they have solved an instrumental task can reduce or eliminate the expansion while the successful behavior remains. As the development of this plasticity depends on the learning strategy used to solve a task, we asked whether the loss of expansion is due to the strategy used during overtraining. Adult male rats were trained in a three-tone auditory discrimination task to bar-press to the CS+ for water reward and refrain from doing so during the CS- tones and silent intertrial intervals; errors were punished by a flashing light and time-out penalty. Groups acquired this task to a criterion within seven training sessions by relying on a strategy that was "bar-press from tone-onset-to-error signal" ("TOTE"). Three groups then received different levels of overtraining: Group ST, none; Group RT, one week; Group OT, three weeks. Post-training mapping of their primary auditory fields (A1) showed that Groups ST and RT had developed significantly expanded representational areas, specifically restricted to the frequency band of the CS+ tone. In contrast, the A1 of Group OT was no different from naïve controls. Analysis of learning strategy revealed this group had shifted strategy to a refinement of TOTE in which they self-terminated bar-presses before making an error ("iTOTE"). Across all animals, the greater the use of iTOTE, the smaller was the representation of the CS+ in A1. Thus, the loss of cortical expansion is attributable to a shift or refinement in strategy. This reversal of expansion was considered in light of a novel theoretical framework (CONCERTO) highlighting four basic principles of brain function that resolve anomalous findings and explaining why even a minor change in strategy would involve concomitant shifts of involved brain sites, including reversal of cortical expansion.