Publications using TDT

Decision-making often involves motivational conflict because of the competing demands of approach and avoidance for a common resource: behavior. This conflict must be resolved as a necessary precursor for adaptive behavior. Here we show a role for the paraventricular thalamus (PVT) in behavioral control during motivational conflict. We used Pavlovian counterconditioning in male rats to establish a conditioned stimulus (CS) as a signal for reward (or danger) and then transformed the same CS into a signal for danger (or reward). After such training, the CS controls conflicting appetitive and aversive behaviors. To assess PVT involvement in conflict, we injected an adeno-associated virus (AAV) expressing the genetically encoded Ca2+ indicator GCaMP and used fiber photometry to record population PVT Ca2+ signals. We show distinct profiles of responsivity across the anterior-posterior axis of PVT during conflict, including an ordinal relationship between posterior PVT CS responses and behavior strength. To study the causal role of PVT in behavioral control during conflict, we injected AAV expressing the inhibitory hM4Di DREADD and determined the effects of chemogenetic PVT inhibition on behavior. We show that chemogenetic inhibition across the anterior-posterior axis of the PVT, but not anterior or posterior PVT alone, disrupts arbitration between appetitive and aversive behaviors when they are in conflict but has no effect when these behaviors are assessed in isolation. Together, our findings identify PVT as central to behavioral control during motivational conflict.SIGNIFICANCE STATEMENT Animals, including humans, approach attractive stimuli and avoid aversive ones. However, they frequently face conflict when the demands of approach and avoidance are incompatible. Resolution of this conflict is fundamental to adaptive behavior. Here we show a role for the paraventricular thalamus, a nucleus of the dorsal midline thalamus, in the arbitration of appetitive and aversive behavior during motivational conflict.

Rat auditory cortex was subjected to 0.1 mA anodal direct current in seven 10-min sessions on alternate days. Based on the well-known auditory cortex control of olivocochlear regulation through corticofugal projections, auditory brainstem responses (ABRs) were recorded as an indirect test of the effectiveness and reversibility of the multisession protocol of epidural stimulation. Increases of 20-30 dB ABR auditory thresholds shown after epidural stimulation reverted back to control levels 10 min after a single session. However, increases in thresholds revert 4 days after multisession stimulation. Less changes in wave amplitudes and threshold shifts were shown in ABR recorded contralaterally to the electrically stimulated side of the brain. To assess tissue effects of epidural electric stimulation on the brain cortex, well characterized functional anatomical markers of glial cells (GFAP/astrocytes and Iba1/microglial cells) and neurons (c-Fos) were analyzed in alternate serial sections by quantitative immunocytochemistry. Restricted astroglial and microglial reactivity was observed within the cytoarchitectural limits of the auditory cortex. However, interstitial GFAP overstaining was also observed in the ventricular surface and around blood vessels, thus supporting a potential global electrolytic stimulation of the brain. These results correlate with extensive changes in the distribution of c-Fos immunoreactive neurons among layers along sensory cortices after multisession stimulation. Quantitative immunocytochemical analysis supported this idea by showing a significant increase in the number of positive neurons in supragranular layers and a decrease in layer 6 with no quantitative changes detected in layer 5. Our data indicate that epidural stimulation of the auditory cortex induces a reversible decrease in hearing sensitivity due to local, restricted epidural stimulation. A global plastic response of the sensory cortices, also reported here, may be related to electrolytic effects of electric currents.

Synchronized states are marked by large-amplitude low-frequency oscillations in the cortex. These states can be seen during quiet waking or slow-wave sleep. Within synchronized states, previous studies have noted a plethora of different types of activity, including delta oscillations (0.5-4 Hz) and slow oscillations (<1 Hz) in the neocortex and large- and small- irregular activity in the hippocampus. However, it is not still fully characterized how neural populations contribute to the synchronized state. Here we apply independent component analysis to parse which populations are involved in different kinds of neocortical activity, and find two populations that alternate throughout synchronized states. One population broadly affects neocortical deep layers, and is associated with larger amplitude slower neocortical oscillations. The other population exhibits theta-frequency oscillations that are not easily observed in raw field potential recordings. These theta oscillations apparently come from below the neocortex, suggesting hippocampal origin, and are associated with smaller amplitude faster neocortical oscillations. Relative involvement of these two alternating populations may indicate different modes of operation within synchronized states.

Adult-onset hearing loss is very common, but we know little about the underlying molecular pathogenesis impeding the development of therapies. We took a genetic approach to identify new molecules involved in hearing loss by screening a large cohort of newly generated mouse mutants using a sensitive electrophysiological test, the auditory brainstem response (ABR). We review here the findings from this screen. Thirty-eight unexpected genes associated with raised thresholds were detected from our unbiased sample of 1,211 genes tested, suggesting extreme genetic heterogeneity. A wide range of auditory pathophysiologies was found, and some mutant lines showed normal development followed by deterioration of responses, revealing new molecular pathways involved in progressive hearing loss. Several of the genes were associated with the range of hearing thresholds in the human population and one, SPNS2, was involved in childhood deafness. The new pathways required for maintenance of hearing discovered by this screen present new therapeutic opportunities.

Infection and inflammation of the middle ears that characterizes acute and chronic otitis media (OM), is a major reason for doctor visits and antibiotic prescription, particularly among children. Nasopharyngeal pathogens that are commonly associated with OM in humans do not naturally colonize the middle ears of rodents, and experimental models in most cases involve directly injecting large numbers of human pathogens into the middle ear bullae of rodents, where they induce a short-lived acute inflammation but fail to persist. Here we report that Bordetella pseudohinzii, a respiratory pathogen of mice, naturally, efficiently and rapidly ascends the eustachian tubes to colonize the middle ears, causing acute and chronic histopathological changes with progressive decrease in hearing acuity that closely mimics otitis media in humans. Laboratory mice experimentally inoculated intranasally with very low numbers of bacteria consistently have their middle ears colonized and subsequently transmit the bacterium to cage mates. Taking advantage of the specifically engineered and well characterized immune deficiencies available in mice we conducted experiments to uncover different roles of T and B cells in controlling bacterial numbers in the middle ear during chronic OM. The iconic mouse model provides significant advantages for elucidating aspects of host-pathogen interactions in otitis media that are currently not possible using other animal models. This natural model of otitis media permits the study of transmission between hosts, efficient early colonization of the respiratory tract, ascension of the eustachian tube, as well as colonization, pathogenesis and persistence in the middle ear. It also allows the combination of the powerful tools of mouse molecular immunology and bacterial genetics to determine the mechanistic basis for these important processes.

The accuracy of the neural code depends on the relative embedding of signal and noise in the activity of neural populations. Despite a wealth of theoretical work on population codes, there are few empirical characterizations of the high-dimensional signal and noise subspaces. We studied the geometry of population codes in the rat auditory cortex across brain states along the activation-inactivation continuum, using sounds varying in difference and mean level across the ears. As the cortex becomes more activated, single-hemisphere populations go from preferring contralateral loud sounds to a symmetric preference across lateralizations and intensities, gain-modulation effectively disappears, and the signal and noise subspaces become approximately orthogonal to each other and to the direction corresponding to global activity modulations. Level-invariant decoding of sound lateralization also becomes possible in the active state. Our results provide an empirical foundation for the geometry and state-dependence of cortical population codes.

Background and objectives: The antioxidant ebselen will be able to limit or prevent the ototoxicity arising from 2-hydroxypropyl-β-cyclodextrin (HPβCD). Niemann-Pick Type C (NPC) disease is a disorder of lysosomal storage manifested in sphingolipidosis. Recently, it was noted that experimental use of HPβCD could partially resolve the symptoms in both animals and human patients. Despite its desirable effect, HPβCD can induce hearing loss, which is the only major side effect noted to date. Understanding of the pathophysiology of hearing impairment after administration of HPβCD and further development of preventive methods are essential to reduce the ototoxic side effect. The mechanisms of HPβCD-induced ototoxicity remain unknown, but the resulting pathology bears some resemblance to other ototoxic agents, which involves oxidative stress pathways. To indirectly determine the involvement of oxidative stress in HPβCD-induced ototoxicity, we tested the efficacy of an antioxidant reagent, ebselen, on the extent of inner ear side effects caused by HPβCD. Materials and methods: Ebselen was applied prior to administration of HPβCD in mice. Auditory brainstem response thresholds and otopathology were assessed one week later. Bilateral effects of the drug treatments also were examined. Results: HPβCD-alone resulted in bilateral, severe, and selective loss of outer hair cells from base to apex with an abrupt transition between lesions and intact areas. Ebselen co-treatment did not ameliorate HPβCD-induced hearing loss or alter the resulting histopathology. Conclusions: The results indirectly suggest that cochlear damage by HPβCD is unrelated to reactive oxygen species formation. However, further research into the mechanism(s) of HPβCD otopathology is necessary.

What determines how we move in the world? Motor neuroscience often focusses either on intrinsic rhythmical properties of motor circuits or extrinsic sensorimotor feedback loops. Here we show that the interplay of both intrinsic and extrinsic dynamics is required to explain the intermittency observed in continuous tracking movements. Using spatiotemporal perturbations in humans, we demonstrate that apparently discrete submovements made 2–3 times per second reflect constructive interference between motor errors and continuous feedback corrections that are filtered by intrinsic circuitry in the motor system. Local field potentials in monkey motor cortex revealed characteristic signatures of a Kalman filter, giving rise to both low-frequency cortical cycles during movement, and delta oscillations during sleep. We interpret these results within the framework of optimal feedback control, and suggest that the intrinsic rhythmicity of motor cortical networks reflects an internal model of external dynamics, which is used for state estimation during feedback-guided movement. Editorial note: This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor's assessment is that all the issues have been addressed (see decision letter).

Super-resolution fluorescence imaging reveals a previously unknown novel structure of spectrin in inner ear hair cells.

Intensity and frequency are the two main properties of sound. The non-monotonic neurons in the auditory system are thought to represent sound intensity. The central nucleus of the inferior colliculus (ICC), as an important information integration nucleus of the auditory system, is also involved in the processing of intensity encoding. Although previous researchers have hinted at the importance of inhibitory effects on the formation of non-monotonic neurons, the specific underlying synaptic mechanisms in the ICC are still unclear. Therefore, we applied the in vivo whole-cell voltage-clamp technique to record the excitatory and inhibitory postsynaptic currents (EPSCs and IPSCs) in the ICC neurons, and compared the effects of excitation and inhibition on the membrane potential outputs. We found that non-monotonic neuron responses could not only be inherited from the lower nucleus but also be created in the ICC. By integrating with a relatively weak IPSC, approximately 35% of the monotonic excitatory inputs remained in the ICC. In the remaining cases, monotonic excitatory inputs were reshaped into non-monotonic outputs by the dominating inhibition at high intensity, which also enhanced the non-monotonic nature of the non-monotonic excitatory inputs.

Neural computations occurring simultaneously in multiple cerebral cortical regions are critical for mediating behaviors. Progress has been made in understanding how neural activity in specific cortical regions contributes to behavior. However, there is a lack of tools that allow simultaneous monitoring and perturbing neural activity from multiple cortical regions. We engineered ‘See-Shells’—digitally designed, morphologically realistic, transparent polymer skulls that allow long-term (>300 days) optical access to 45 mm 2 of the dorsal cerebral cortex in the mouse. We demonstrate the ability to perform mesoscopic imaging, as well as cellular and subcellular resolution two-photon imaging of neural structures up to 600 µm deep. See-Shells allow calcium imaging from multiple, non-contiguous regions across the cortex. Perforated See-Shells enable introducing penetrating neural probes to perturb or record neural activity simultaneously with whole cortex imaging. See-Shells are constructed using common desktop fabrication tools, providing a powerful tool for investigating brain structure and function.

Mitogen-activated protein kinases (MAPK) such as p38 and the c-Jun N-terminal kinases (JNKs) are activated during the cellular response to stress signals. Their activity is regulated by the MAPK-phosphatase 1 (DUSP1), a key component of the anti-inflammatory response. Stress kinases are well-described elements of the response to otic injury and the otoprotective potential of JNK inhibitors is being tested in clinical trials. By contrast, there are no studies exploring the role of DUSP1 in hearing and hearing loss. Here we show that Dusp1 expression is age-regulated in the mouse cochlea. Dusp1 gene knock-out caused premature progressive hearing loss, as confirmed by auditory evoked responses in Dusp1 –/ – mice. Hearing loss correlated with cell death in hair cells, degeneration of spiral neurons and increased macrophage infiltration. Dusp1 –/ – mouse cochleae showed imbalanced redox status and dysregulated expression of cytokines. These data suggest that DUSP1 is essential for cochlear homeostasis in the response to stress during ageing.

Two experiments were performed to better understand on- and off-frequency modulation masking in normal-hearing school-age children and adults. Experiment 1 estimated thresholds for detecting 16-, 64- or 256-Hz sinusoidal amplitude modulation (AM) imposed on a 4300-Hz pure tone. Thresholds tended to improve with age, with larger developmental effects for 64- and 256-Hz AM than 16-Hz AM. Detection of 16-Hz AM was also measured with a 1000-Hz off-frequency masker tone carrying 16-Hz AM. Off-frequency modulation masking was larger for younger than older children and adults when the masker was gated with the target, but not when the masker was continuous. Experiment 2 measured detection of 16- or 64-Hz sinusoidal AM carried on a bandpass noise with and without additional on-frequency masker AM. Children and adults demonstrated modulation masking with similar tuning to modulation rate. Rate-dependent age effects for AM detection on a pure-tone carrier are consistent with maturation of temporal resolution, an effect that may be obscured by modulation masking for noise carriers. Children were more susceptible than adults to off-frequency modulation masking for gated stimuli, consistent with maturation in the ability to listen selectively in frequency, but the children were not more susceptible to on-frequency modulation masking than adults.

Fragile X syndrome (FXS) is characterized by hypersensitivity to sensory stimuli, including environmental sounds. We compared the auditory brainstem response (ABR) recorded in vivo in mice lacking the gene (Fmr1-/y ) for fragile X mental retardation protein (FMRP) with that in wild-type animals. We found that ABR wave I, which represents input from the auditory nerve, is reduced in Fmr1-/y animals, but only at high sound levels. In contrast, wave IV, which represents the activity of auditory brainstem nuclei is enhanced at all sound levels, suggesting that loss of FMRP alters the central processing of auditory signals. Current-clamp recordings of neurons in the medial nucleus of the trapezoid body in the auditory brainstem revealed that, in contrast to neurons from wild-type animals, sustained depolarization triggers repetitive firing rather than a single action potential. In voltage-clamp recordings, K+ currents that activate at positive potentials ("high-threshold" K+ currents), which are required for high-frequency firing and are carried primarily by Kv3.1 channels, are elevated in Fmr1-/y mice, while K+ currents that activate near the resting potential and inhibit repetitive firing are reduced. We therefore tested the effects of AUT2 [((4-({5-[(4R)-4-ethyl-2,5-dioxo-1-imidazolidinyl]-2-pyridinyl}oxy)-2-(1-methylethyl) benzonitrile], a compound that modulates Kv3.1 channels. AUT2 reduced the high-threshold K+ current and increased the low-threshold K+ currents in neurons from Fmr1-/y animals by shifting the activation of the high-threshold current to more negative potentials. This reduced the firing rate and, in vivo, restored wave IV of the ABR. Our results from animals of both sexes suggest that the modulation of the Kv3.1 channel may have potential for the treatment of sensory hypersensitivity in patients with FXS.SIGNIFICANCE STATEMENT mRNA encoding the Kv3.1 potassium channel was one of the first described targets of the fragile X mental retardation protein (FMRP). Fragile X syndrome is caused by loss of FMRP and, in humans and mice, causes hypersensitivity to auditory stimuli. We found that components of the auditory brain response (ABR) corresponding to auditory brainstem activity are enhanced in mice lacking FMRP. This is accompanied by hyperexcitability and altered potassium currents in auditory brainstem neurons. Treatment with a drug that alters the voltage dependence of Kv3.1 channels normalizes the imbalance of potassium currents, as well as ABR responses in vivo, suggesting that such compounds may be effective in treating some symptoms of fragile X syndrome.

Salience is a broad and widely used concept in neuroscience whose neuronal correlates, however, remain elusive. In behavioral conditioning, salience is used to explain various effects, such as stimulus overshadowing, and refers to how fast and strongly a stimulus can be associated with a conditioned event. Here, we identify sounds of equal intensity and perceptual detectability, which due to their spectro-temporal content recruit different levels of population activity in mouse auditory cortex. When using these sounds as cues in a Go/NoGo discrimination task, the degree of cortical recruitment matches the salience parameter of a reinforcement learning model used to analyze learning speed. We test an essential prediction of this model by training mice to discriminate light-sculpted optogenetic activity patterns in auditory cortex, and verify that cortical recruitment causally determines association or overshadowing of the stimulus components. This demonstrates that cortical recruitment underlies major aspects of stimulus salience during reinforcement learning.

Adults with bilateral cochlear implants (BiCIs) receive benefits in localizing stationary sounds when listening with two implants compared with one; however, sound localization ability is significantly poorer when compared to normal hearing (NH) listeners. Little is known about localizing sound sources in motion, which occurs in typical everyday listening situations. The authors considered the possibility that sound motion may improve sound localization in BiCI users by providing multiple places of information. Alternatively, the ability to compare multiple spatial locations may be compromised in BiCI users due to degradation of binaural cues, and thus result in poorer performance relative to NH adults. In this study, the authors assessed listeners' abilities to distinguish between sounds that appear to be moving vs stationary, and track the angular range and direction of moving sounds. Stimuli were bandpass-filtered (150–6000 Hz) noise bursts of different durations, panned over an array of loudspeakers. Overall, the results showed that BiCI users were poorer than NH adults in (i) distinguishing between a moving vs stationary sound, (ii) correctly identifying the direction of movement, and (iii) tracking the range of movement. These findings suggest that conventional cochlear implant processors are not able to fully provide the cues necessary for perceiving auditory motion correctly.

Natural sounds have rich spectrotemporal dynamics. Spectral information is spatially represented in the auditory cortex (ACX) via large-scale maps. However, the representation of temporal information, e.g., sound offset, is unclear. We perform multiscale imaging of neuronal and thalamic activity evoked by sound onset and offset in awake mouse ACX. ACX areas differed in onset responses (On-Rs) and offset responses (Off-Rs). Most excitatory L2/3 neurons show either On-Rs or Off-Rs, and ACX areas are characterized by differing fractions of On and Off-R neurons. Somatostatin and parvalbumin interneurons show distinct temporal dynamics, potentially amplifying Off-Rs. Functional network analysis shows that ACX areas contain distinct parallel onset and offset networks. Thalamic (MGB) terminals show either On-Rs or Off-Rs, indicating a thalamic origin of On and Off-R pathways. Thus, ACX areas spatially represent temporal features, and this representation is created by spatial convergence and co-activation of distinct MGB inputs and is refined by specific intracortical connectivity.

Cisplatin-induced ototoxicity results in significant, permanent hearing loss in pediatric and adult cancer survivors. Elucidating the mechanisms underlying cisplatin-induced hearing loss as well as the development of therapies to reduce and/or reverse cisplatin ototoxicity have been impeded by suboptimal animal models. Clinically, cisplatin is most commonly administered in multi-dose, multi-cycle protocols. However, many animal studies are conducted using single injections of high-dose cisplatin, which is not reflective of clinical cisplatin administration protocols. Significant limitations of both high-dose, single-injection protocols and previous multi-dose protocols in rodent models include high mortality rates and relatively small changes in hearing sensitivity. These limitations restrict assessment of both long-term changes in hearing sensitivity and effects of potential protective therapies. Here, we present a detailed method for an optimized mouse model of cisplatin ototoxicity that utilizes a multi-cycle administration protocol that better approximates the type and degree of hearing loss observed clinically. This protocol results in significant hearing loss with very low mortality. This mouse model of cisplatin ototoxicity provides a platform for examining mechanisms of cisplatin-induced hearing loss as well as developing therapies to protect the hearing of cancer patients receiving cisplatin therapy.

The cochlear microphonic, traditionally thought of as an indication of electrical current flow through hair cells, in conjunction with suppressing high-pass noise or tones, is a promising method of assessing the health of outer hair cells at specific locations along the cochlear partition. We propose that the electrical potential recorded from the round window in gerbils in response to low-frequency tones, which we call cochlear response (CR), contains significant responses from multiple cellular sources, which may expand its diagnostic purview. In this study, CR is measured in the gerbil and modeled to identify its contributing sources. CR was recorded via an electrode placed in the round window niche of sixteen Mongolian gerbils and elicited with a 45 Hz tone burst embedded in 18 high-pass filtered noise conditions to target responses from increasing regions along the cochlear partition. Possible sources were modeled using previously-published hair cell and auditory nerve response data, and then weighted and combined using linear regression to produce a model response that fits closely to the mean CR waveform. The significant contributing sources identified by the model are outer hair cells, inner hair cells, and the auditory nerve. We conclude that the low-frequency CR contains contributions from several cellular sources.

An inductively-powered wireless integrated neural recording and stimulation (WINeRS-8) system-on-a-chip (SoC) that is compatible with the EnerCage-HC2 for wireless/battery-less operation has been presented for neuroscience experiments on freely behaving animals. WINeRS-8 includes a 32-ch recording analog front end, a 4-ch current-controlled stimulator, and a 434 MHz on - off keying data link to an external software- defined radio wideband receiver (Rx). The headstage also has a bluetooth low energy link for controlling the SoC. WINeRS-8/EnerCage-HC2 systems form a bidirectional wireless and battery-less neural interface within a standard homecage, which can support longitudinal experiments in an enriched environment. Both systems were verified in vivo on rat animal model, and the recorded signals were compared with hardwired and battery-powered recording results. Realtime stimulation and recording verified the system's potential for bidirectional neural interfacing within the homecage, while continuously delivering 35 mW to the hybrid WINeRS-8 headstage over an unlimited period.