Publications using TDT

Background To localize sound sources accurately in a reverberant environment, human binaural hearing strongly favors analyzing the initial wave front of sounds. Behavioral studies of this “precedence effect” have so far largely been confined to human subjects, limiting the scope of complementary physiological approaches. Similarly, physiological studies have mostly looked at neural responses in the inferior colliculus, the main relay point between the inner ear and the auditory cortex, or used modeling of cochlear auditory transduction in an attempt to identify likely underlying mechanisms. Studies capable of providing a direct comparison of neural coding and behavioral measures of sound localization under the precedence effect are lacking. Results We adapted a “temporal weighting function” paradigm previously developed to quantify the precedence effect in human for use in laboratory rats. The animals learned to lateralize click trains in which each click in the train had a different interaural time difference. Computing the “perceptual weight” of each click in the train revealed a strong onset bias, very similar to that reported for humans. Follow-on electrocorticographic recording experiments revealed that onset weighting of interaural time differences is a robust feature of the cortical population response, but interestingly, it often fails to manifest at individual cortical recording sites. Conclusion While previous studies suggested that the precedence effect may be caused by early processing mechanisms in the cochlea or inhibitory circuitry in the brainstem and midbrain, our results indicate that the precedence effect is not fully developed at the level of individual recording sites in the auditory cortex, but robust and consistent precedence effects are observable only in the auditory cortex at the level of cortical population responses. This indicates that the precedence effect emerges at later cortical processing stages and is a significantly “higher order” feature than has hitherto been assumed.

Covert visual attention is accomplished by a cascade of mechanisms distributed across multiple brain regions. Visual cortex is associated with enhanced representations of relevant stimulus features, whereas the contributions of subcortical circuits are less well understood but have been associated with selection of relevant spatial locations and suppression of distracting stimuli. As a step toward understanding these subcortical circuits, here we identified how neuronal activity in the intermediate layers of the superior colliculus (SC) of head-fixed mice is modulated during covert visual attention. We found that spatial cues modulated both firing rate and spike-count correlations. Crucially, the cue-related modulation in firing rate was due to enhancement of activity at the cued spatial location rather than suppression at the uncued location, indicating that SC neurons in our task were modulated by an excitatory or disinhibitory circuit mechanism focused on the relevant location, rather than broad inhibition of irrelevant locations. This modulation improved the neuronal discriminability of visual-change-evoked activity, but only when assessed for neuronal activity between the contralateral and ipsilateral SC. Together, our findings indicate that neurons in the mouse SC can contribute to covert visual selective attention by biasing processing in favor of locations expected to contain task-relevant information.

Disruption of subthalamic nucleus dynamics in Parkinson’s disease leads to impairments during walking. Here, we aimed to uncover the principles through which the subthalamic nucleus encodes functional and dysfunctional walking in people with Parkinson’s disease. We conceived a neurorobotic platform that allowed us to deconstruct the key components of walking under well-controlled conditions. We exploited this platform in 18 patients with Parkinson’s disease, which allowed us to demonstrate that the subthalamic nucleus encodes the initiation, termination, and vigor of leg muscle activation. We found that the same fundamental principles determine the encoding of walking. We translated this understanding into a machine-learning framework that decoded muscle activation, walking states, locomotor vigor, and freezing of gait. These results expose key principles through which subthalamic nucleus dynamics encode walking, opening the possibility to operate neuroprosthetic systems with these signals to improve walking in people with Parkinson’s disease. One Sentence Summary The subthalamic nucleus encodes the initiation, termination, and vigor of muscle activity, which supports real-time decoding of gait in people with Parkinson’s disease.

Cell cycle associated protein 1 (Caprin1) is an RNA-binding protein that can regulate the cellular post-transcriptional response to stress. It is a component of both stress granules and neuronal RNA granules and is implicated in neurodegenerative disease, synaptic plasticity and long-term memory formation. Our previous work suggested that Caprin1 also plays a role in the response of the cochlea to stress. Here, targeted inner ear-deletion of Caprin1 in mice leads to an early onset, progressive hearing loss. Auditory brainstem responses from Caprin1 -deficient mice show reduced thresholds, with a significant reduction in wave-I amplitudes compared to wildtype. Whilst hair cell structure and numbers were normal, the inner hair cell-spiral ganglion neuron (IHC-SGN) synapse revealed abnormally large post-synaptic GluA2 receptor puncta, a defect consistent with the observed wave-I reduction. Unlike wildtype mice, mild-noise-induced hearing threshold shifts in Caprin1 -deficient mice did not recover. Oxidative stress triggered TIA-1/HuR-positive stress granule formation in ex-vivo cochlear explants from Caprin1- deficient mice, showing that stress granules could still be induced. Taken together, these findings suggest that Caprin1 plays a key role in maintenance of auditory function, where it regulates the normal status of the IHC-SGN synapse.

Survival relies on an organism’s intrinsic ability to instinctively react to stimuli such as food, water, and threats, ensuring the fundamental ability to feed, drink, and avoid danger even in the absence of prior experience. These natural, unconditioned stimuli can also facilitate associative learning, where pairing them consistently with neutral cues will elicit responses to those cue. Threat conditioning, a well-explored form of associative learning, commonly employs painful electric shocks, mimicking injury, as unconditioned stimuli. It remains elusive whether actual injury or pain is necessary for effective learning, or whether the threat of harm is sufficient. Approaching predators create looming shadows and sounds, triggering strong innate defensive responses like escape and freezing. This study investigates whether visual looming stimuli can induce learned freezing or learned escape responses to a conditioned stimulus in rats. Surprisingly, pairing a neutral tone with a looming stimulus only weakly evokes learned defensive responses, in contrast to the strong responses observed when the looming stimulus is replaced by a shock. This dissociation sheds light on the boundaries for learned defensive responses thereby impacting our comprehension of learning processes and defensive strategies.

Mu opioid receptor (MOR) agonists are potent analgesics, but also cause sedation, respiratory depression, and addiction risk. The epithalamic lateral habenula (LHb) signals aversive states including pain, and here we found that it is a potent site for MOR-agonist analgesia-like responses in rats. Importantly, LHb MOR activation is not reinforcing in the absence of noxious input. The LHb receives excitatory inputs from multiple sites including the ventral tegmental area, lateral hypothalamus, entopeduncular nucleus, and the lateral preoptic area of the hypothalamus (LPO). Here we report that LHb-projecting glutamatergic LPO neurons are excited by noxious stimulation and are preferentially inhibited by MOR selective agonists. Critically, optogenetic stimulation of LHb-projecting LPO neurons produces an aversive state that is relieved by LHb MOR activation, and optogenetic inhibition of LHb-projecting LPO neurons relieves the aversiveness of ongoing pain.

Ultrasound (US) has been shown to stimulate brain circuits, however, the ability to excite peripheral nerves with US remains controversial. To the best of our knowledge, there is still no in vivo neural recording study that has applied US stimulation to a nerve isolated from surrounding tissue to confirm direct activation effects. Here, we show that US cannot excite an isolated mammalian sciatic nerve in an in vivo preparation, even at high pressures (relative to levels recommended in the FDA guidance for diagnostic ultrasound) and for a wide range of parameters, including different pulse patterns and center frequencies. US can, however, reliably inhibit nerve activity whereby greater suppression is correlated with increases in nerve temperature. By prohibiting the nerve temperature from increasing during US application, we did not observe suppressive effects. Overall, these findings demonstrate that US can reliably inhibit nerve activity through a thermal mechanism that has potential for various health disorders, though future studies are needed to evaluate the long-term safety of therapeutic ultrasound applications.

Electrocorticography (ECoG) is a conventional, invasive technique for recording brain signals from the cortical surface using an array of electrodes. In this study, we developed a highly flexible 22-channel ECoG microelectrode array on a thin Parylene film using novel fabrication techniques. Narrow (<40 µm) and thin (<500 nm) microelectrode patterns were first printed on PDMS, then the patterns were transferred onto Parylene films via vapor deposition and peeling. A custom-designed, 3D-printed connector was built and assembled with the Parylene-based flexible ECoG microelectrode array without soldering. The impedance of the assembled ECoG electrode array was measured in vitro by electrochemical impedance spectroscopy, and the result was consistent. In addition, we conducted in vivo studies by implanting the flexible ECoG sensor in a rat and successfully recording brain signals.

The excessive generation of reactive oxygen species (ROS) and mitochondrial damage have been widely reported in noise-induced hearing loss (NIHL). However, the specific mechanism of noise-induced mitochondrial damage remains largely unclear. In this study, we showed that acoustic trauma caused oxidative damage to mitochondrial DNA (mtDNA), leading to the reduction of mtDNA content, mitochondrial gene expression and ATP level in rat cochleae. The expression level and mtDNA-binding function of mitochondrial transcription factor A (TFAM) were impaired following acoustic trauma without affecting the upstream PGC-1α and NRF-1. The mitochondria-target antioxidant mito-TEMPO (MT) was demonstrated to enter the inner ear after the systemic administration. MT treatment significantly alleviated noise-induced auditory threshold shifts 3d and 14d after noise exposure. Furthermore, MT significantly reduced outer hair cell (OHC) loss, cochlear ribbon synapse loss, and auditory nerve fiber (ANF) degeneration after the noise exposure. In addition, we found that MT treatment effectively attenuated noise-induced cochlear oxidative stress and mtDNA damage, as indicated by DHE, 4-HNE, and 8-OHdG. MT treatment also improved mitochondrial biogenesis, ATP generation, and TFAM-mtDNA interaction in the cochlea. These findings suggest that MT has protective effects against NIHL via maintaining TFAM-mtDNA interaction and mitochondrial biogenesis based on its ROS scavenging capacity.

The ability to determine a sound’s location is critical in everyday life. However, sound source localization is severely compromised for patients with hearing loss who receive bilateral cochlear implants (BiCIs). Several patient factors relate to poorer performance in listeners with BiCIs, associated with auditory deprivation, experience, and age. Critically, characteristic errors are made by patients with BiCIs (e.g., medial responses at lateral target locations), and the relationship between patient factors and the type of errors made by patients has seldom been investigated across individuals. In the present study, several different types of analysis were used to understand localization errors and their relationship with patient-dependent factors (selected based on their robustness of prediction). Binaural hearing experience is required for developing accurate localization skills, auditory deprivation is associated with degradation of the auditory periphery, and aging leads to poorer temporal resolution. Therefore, it was hypothesized that earlier onsets of deafness would be associated with poorer localization acuity and longer periods without BiCI stimulation or older age would lead to greater amounts of variability in localization responses. A novel machine learning approach was introduced to characterize the types of errors made by listeners with BiCIs, making them simple to interpret and generalizable to everyday experience. Sound localization performance was measured in 48 listeners with BiCIs using pink noise trains presented in free-field. Our results suggest that older age at testing and earlier onset of deafness are associated with greater average error, particularly for sound sources near the center of the head, consistent with previous research. The machine learning analysis revealed that variability of localization responses tended to be greater for individuals with earlier compared to later onsets of deafness. These results suggest that early bilateral hearing is essential for best sound source localization outcomes in listeners with BiCIs.

Before hearing onset (postnatal day 12 in mice), inner hair cells (IHCs) spontaneously fire action potentials, thereby driving pre-sensory activity in the ascending auditory pathway. The rate of IHC action potential bursts is modulated by inner supporting cells (ISCs) of Kölliker’s organ through the activity of the Ca 2+ -activated Cl - -channel TMEM16A (ANO1). Here, we show that conditional deletion of Ano1 ( Tmem16a ) in mice disrupts Ca 2+ waves within Kölliker’s organ, reduces the burst-firing activity and the frequency selectivity of auditory brainstem neurons in the medial nucleus of the trapezoid body (MNTB), and also impairs the functional refinement of MNTB projections to the lateral superior olive. These results reveal the importance of the activity of Kölliker’s organ for the refinement of central auditory connectivity. In addition, our study suggests the involvement of TMEM16A in the propagation of Ca 2+ waves, which may also apply to other tissues expressing TMEM16A.

Several studies identified hearing loss as a risk factor for aging-related processes, including neurodegenerative diseases, as dementia and age-related hearing loss (ARHL). Although the association between hearing impairment in midlife and ARHL has been widely documented by epidemiological and experimental studies, the molecular mechanisms underlying this association are not fully understood. In this study, we used an established animal model of ARHL (C57BL/6 mice) to evaluate if early noise-induced hearing loss (NIHL) could affect the onset or progression of age-related cochlear dysfunction. We found that hearing loss can exacerbate ARHL, damaging sensory-neural cochlear epithelium and causing synaptopathy. Moreover, we studied common pathological markers shared between hearing loss and ARHL, demonstrating that noise exposure can worsen/accelerate redox status imbalance [increase of reactive oxygen species (ROS) production, lipid peroxidation, and dysregulation of endogenous antioxidant response] and vascular dysfunction [increased expression of hypoxia-inducible factor-1alpha (HIF-1α) and vascular endothelial growth factor C (VEGFC)] in the cochlea. Unveiling the molecular mechanisms underlying the link between hearing loss and aging processes could be valuable to identify effective therapeutic strategies to limit the effect of environmental risk factors on age-related diseases.

Although the etiology of major depressive disorder remains poorly understood, impairment of gamma oscillations recently emerged as a potential biomarker for major depression. The olfactory bulb (OB) is a major source of brain wide gamma oscillations and bulbectomy is an animal model for depression. Here we demonstrate that chemogenetic suppression of OB neuronal activity or temporally suppressing the OB to pyriform cortex synaptic transmission decreased gamma oscillation power in multiple brain areas associated with depression-like behaviors. To assess the hypothesized link between depression and diffuse depression of gamma oscillations, we employed gamma phase-dependent closed loop neuromodulation of cortical areas, paced by the native OB output. This procedure alleviated depressive-like behaviors in animals and suggests that restoring gamma oscillations may improve depression in humans. One Sentence Summary Role of limbic gamma oscillations in depression

In the mammalian brain, auditory brainstem nuclei are arranged topographically according to acoustic frequency responsiveness. During postnatal development, the axon initial segment (AIS) of principal neurons undergoes structural refinement depending on location along the tonotopic axis within the medial nucleus of the trapezoid body (MNTB). However, the molecular mechanisms underlying the structural refinement of the AIS along the tonotopic axis in the auditory brainstem have not been explored. We tested the hypothesis that brain-derived neurotrophic factor (BDNF) is a molecular mediator of the structural development of the MNTB in an activity-dependent manner. Using BDNF heterozygous mutant ( BDNF +/– ) mice, we examined the impact of global BDNF reduction on structural and functional development of MNTB neurons by assessing AIS structure and associated intrinsic neuronal properties. BDNF reduction inhibits the structural and functional differentiation of principal neurons along the tonotopic axis in the MNTB. Augmented sound input during the critical period of development has been shown to enhance the structural refinement of the AIS of MNTB neurons. However, in BDNF +/– mice, MNTB neurons did not show this activity-dependent structural modification of the AIS following repeated sound stimulation. In addition, BDNF +/– mice lacked a defined isofrequency band of neuronal activity following exposure to 16 kHz sound, suggesting degradation of tonotopy. Taken together, structural development and functional refinement of auditory brainstem neurons require physiological levels of BDNF to establish proper tonotopic gradients.

A previous investigation demonstrated differences between younger adult normal-hearing listeners and older adult hearing-impaired listeners in the perceived emotion of clear and conversational speech. Specifically, clear speech sounded angry more often than conversational speech for both groups, but the effect was smaller for the older listeners. These listener groups differed by two confounding factors, age (younger vs. older adults) and hearing status (normal vs. impaired). The objective of the present study was to evaluate the contributions of aging and hearing loss to the reduced perception of anger in older adults with hearing loss. We investigated perceived anger in clear and conversational speech in younger adults with and without a simulated age-related hearing loss, and in older adults with normal hearing. Younger adults with simulated hearing loss performed similarly to normal-hearing peers, while normal-hearing older adults performed similarly to hearing-impaired peers, suggesting that aging was the primary contributor to the decreased anger perception seen in previous work. These findings confirm reduced anger perception for older adults compared to younger adults, though the significant speaking style effect—regardless of age and hearing status—highlights the need to identify methods of producing clear speech that is emotionally neutral or positive.

Objective. Extracellular microelectrode techniques are the most widely used approach to interrogate neuronal populations. However, regardless of the manufacturing method used, damage to the vasculature and circuit function during probe insertion remains a concern. This issue can be mitigated by minimising the footprint of the probe used. Reducing the size of probes typically requires either a reduction in the number of channels present in the probe, or a reduction in the individual channel area. Both lead to less effective coupling between the probe and extracellular signals of interest. Approach. Here, we show that continuously drawn SiO 2 -insulated ultra-microelectrode fibres offer an attractive substrate to address these challenges. Individual fibres can be fabricated to >10 m continuous stretches and a selection of diameters below 30 µ m with low resistance (<100 Ω mm −1 ) continuously conductive metal core of <10 µ m and atomically flat smooth shank surfaces. To optimize the properties of the miniaturised electrode-tissue interface, we electrodeposit rough Au structures followed by ∼20 nm IrOx film resulting in the reduction of the interfacial impedance to <500 kΩ at 1 kHz. Main results . We demonstrate that these ultra-low impedance electrodes can record and stimulate both single and multi-unit activity with minimal tissue disturbance and exceptional signal-to-noise ratio in both superficial (∼40 µ m) and deep (∼6 mm) structures of the mouse brain. Further, we show that sensor modifications are stable and probe manufacturing is reproducible. Significance. Minimally perturbing bidirectional neural interfacing can reveal circuit function in the mammalian brain in vivo.

Across-frequency binaural interference occurs when the sensitivity to changes in interaural differences in a target sound is decreased by a spectrally remote diotic interfering sound. For interaural time differences (ITDs), low-frequency (e.g., 0.5 kHz) interferers cause more interference on high-frequency (e.g., 4 kHz) targets than vice versa. For interaural level differences (ILDs), however, it is unclear if a frequency dependence exists. Therefore, ILD discrimination thresholds and across-frequency binaural interference were measured for target and interferer frequencies between 0.5 and 8 kHz (for tones) or 12 kHz (for narrowband noises). For tones, 8-kHz targets experienced the least interference and 8-kHz interferers produced the most interference, suggesting that higher-frequency ILDs are a more heavily weighted localization cue than lower-frequency ILDs. For narrowband noises, the frequency-dependent interference patterns increased in complexity in comparison to tones. Low-frequency ITD dominance (from randomly varying onset ITDs) and grouping cues (e.g., envelope modulations) might explain some of the complexity in the interference patterns for the noises. These data contribute to a better understanding of across-frequency ILD processing, which remains poorly understood.

The central nervous system has long been thought to regulate insulin secretion, an essential process in the maintenance of blood glucose levels. However, the anatomical and functional connections between the brain and insulin-producing pancreatic β cells remain undefined. Here, we describe a functional transneuronal circuit connecting the hypothalamus to β cells in mice. This circuit originates from a subpopulation of oxytocin neurons in the paraventricular hypothalamic nucleus (PVNOXT), and it reaches the islets of the endocrine pancreas via the sympathetic autonomic branch to innervate β cells. Stimulation of PVNOXT neurons rapidly suppresses insulin secretion and causes hyperglycemia. Conversely, silencing of these neurons elevates insulin levels by dysregulating neuronal signaling and secretory pathways in β cells and induces hypoglycemia. PVNOXT neuronal activity is triggered by glucoprivation. Our findings reveal that a subset of PVNOXT neurons form functional multisynaptic circuits with β cells in mice to regulate insulin secretion, and their function is necessary for the β cell response to hypoglycemia.

The transition from wakefulness to sleep requires striking alterations in brain activity, physiology, and behavior, yet the precise neuronal circuit elements facilitating this transition remain unclear. Prior to sleep onset, many animal species display characteristic behaviors, including finding a safe location, performing hygiene-related behaviors, and preparing a space for sleep. It has been proposed that the pre-sleep period is a transitional phase in which engaging in a specific behavioral repertoire de-arouses the brain and facilitates the wake-to-sleep transition, yet both causal evidence for this premise and an understanding of the neuronal circuit elements involved are lacking. Here, we combine detailed behavioral observations, EEG-EMG recordings, selective targeting, and activity modulation of pre-sleep-active neurons to reveal the behaviors preceding sleep initiation and their underlying neurobiological mechanisms. We show that mice engage in temporally structured behaviors with stereotypic EEG signatures prior to sleep and that nest-building and grooming become significantly more prevalent with sleep proximity. We next demonstrate that the ability to build a nest promotes the initiation and consolidation of sleep and that the lack of nesting material chronically fragments sleep. Lastly, we identify broadly projecting and predominantly glutamatergic neuronal ensembles in the lateral hypothalamus that regulate the motivation to engage in pre-sleep nest-building behavior and gate sleep initiation and intensity. Our study provides causal evidence for the facilitatory role of pre-sleep behaviors in sleep initiation and consolidation and a functional characterization of the neuronal underpinnings regulating a sleep-related and goal-directed complex behavior.

The primary startle response (SR) is an innate reaction evoked by sudden and intense acoustic, tactile or visual stimuli. In rodents and humans the SR involves reflexive contractions of the face, neck and limb muscles. The acoustic startle response (ASR) pathway consists of auditory nerve fibers (AN), cochlear root neurons (CRNs) and giant neurons of the caudal pontine reticular nucleus (PnC), which synapse on cranial and spinal motor neurons. The tactile startle response (TSR) is transmitted by primary sensory neurons to the principal sensory (Pr5) and spinal (Sp5) trigeminal nuclei. The ventral part of Pr5 projects directly to the PnC neurons. The SR requires rapid transmission of sensory information to initiate a fast motor response. Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPAR) are necessary to transmit auditory information to the PnC neurons and elicit the SR. AMPARs containing the glutamate AMPAR subunit 4 (GluA4) have fast kinetics, which makes them ideal candidates to transmit the SR signal. This study examined the role of GluA4 within the primary SR pathway by using GluA4 knockout (GluA4-KO) mice. Deletion of GluA4 considerably decreased the amplitude and probability of successful ASR and TSR, indicating that the presence of this subunit is critical at a common station within the startle pathway. We conclude that deletion of GluA4 affects the transmission of sensory signals from acoustic and tactile pathways to the motor component of the startle reflex. Therefore, GluA4 is required for the full response and for reliable elicitation of the startle response.