Neuroscience Research

Neuromodulatory systems regulate neural circuits across broad regions of the brain, and disruption of the dopaminergic system contributes to psychiatric and neurodegenerative disorders. Engineered viral vectors have been used to target the neuromodulatory systems of the nonhuman primate brain (Y. Chen et al., 2023; El-Shamayleh et al., 2016; Gray et al., 2010; Lerchner et al., 2014; Perez et al., 2022). However, a conspicuous obstacle to the isolation and modulation of specific pathways is the inability of many retrogradely infecting viruses to transduce dopaminergic (DA) cells efficiently (Tervo et al., 2016; Cushnie et al., 2020; Weiss et al., 2020). We compare the DA neuron retrograde transduction efficacy of four viral vectors after injection into the striatum of nonhuman primates (NHP). Selectivity was assessed by comparing the neuronal co-expression of fluorescent reporter protein and tyrosine-hydroxylase (TH) antibody in substantia nigra pars compacta (SNc). The rabies pseudotyped lentiviral vector, FuG-B2, produced superior retrograde transduction of DA cells to FuG-C or FuG-E. AAV2.retro was the least effective.

Acoustic simulations of cochlear implants (CIs) allow for studies of perceptual performance with minimized effects of large CI individual variability. Different from conventional simulations using continuous sinusoidal or noise carriers, the present study employs pulsatile Gaussian-enveloped tones (GETs) to simulate several key features in modern CIs. Subject to the time-frequency uncertainty principle, the GET has a well-defined tradeoff between its duration and bandwidth. Two types of GET vocoders were implemented and evaluated in normal-hearing listeners. In the first implementation, constant 100-Hz GETs were used to minimize within-channel temporal overlap while different GET durations were used to simulate electric channel interaction. This GET vocoder could produce vowel and consonant recognition similar to actual CI performance. In the second implementation, 900-Hz/channel pulse trains were directly mapped to 900-Hz GET trains to simulate the maxima selection and amplitude compression of a widely-used n-of-m processing strategy, or the Advanced Combination Encoder. The simulated and actual implant performance of speech-in-noise recognition was similar in terms of the overall trend, absolute mean scores, and standard deviations. The present results suggest that the pulsatile GET vocoders can be used as alternative vocoders to simultaneously simulate several key CI processing features and result in similar speech perception performance to that with modern CIs.

Animals properly perform sexual behaviors by using multiple sensory cues. However, neural mechanisms integrating multiple sensory cues and regulating motivation for sexual behaviors remain unclear. Here, we focused on peptidergic neurons, terminal nerve gonadotropin-releasing hormone (TN-GnRH) neurons, which receive inputs from various sensory systems and co-express neuropeptide FF (NPFF) in addition to GnRH. Our behavioral analyses using knockout medaka of GnRH (gnrh3) and/or NPFF (npff) demonstrated that some sexual behavioral repertories were delayed, not disrupted, in gnrh3-/- and npff-/- males, while the double knockout showed normal behaviors. We also found anatomical evidence to show that both neuropeptides modulate the sexual behavior-controlling brain areas. Furthermore, we demonstrated that NPFF activates neurons in the preoptic area via indirect pathway, which is considered to induce the increase in the motivation for male sexual behaviors. Considering these results, we propose a novel mechanism by which balanced release of co-existing peptides is important for the neuromodulatory function of TN-GnRH neurons in the control of behavioral motivation. Our results may go a long way toward understanding the functional significance of peptidergic neuromodulation in response to external environments.

Accumulating evidence indicates that the molecular circadian clock underlies the mating behavior of Drosophila melanogaster. However, information about which gene affects circadian mating behavior is poorly understood in animals. The present study found that feeding Myo-inositol enhanced the close-proximity (CP) rhythm of D. melanogaster mating behavior and lengthened the period of the CP rhythm. Then, to understand a role for inositol synthesis to fly mating behavior, we established the Inos (Myo-inositol 1-phosphate synthase) gene knock down fly strains with RNAi. Interestingly, the CP behavior of this three-different driver knock down strains was arrhythmic, but the locomotor rhythm was rhythmic. The data of three-different Inos knock down strains suggests that Inos gene expression of upper LNd, l-LNV, 5ths-LNv in brain is necessary for proper CP rhythm generation in D. melanogaster. The data indicated that the Inos gene is involved in the role for the circadian rhythm of D. melanogaster mating behavior.

Neurotropic virus tracers, particularly those with low toxicity and high efficient tracing, are powerful tools for structural and functional dissections of neural circuits. The retrograde trans-mono-synaptic technology based on rabies virus CVS-N2c strain has reduced cytotoxicity and enhanced efficiency, attains long-term gene manipulation for functional studies, but suffers from difficult preparation and low yield. To overcome these shortcomings, an improved production system was established for rapid rescue and preparation of CVS-N2c-{Delta}G virus, CVS-N2c-{Delta}G with the same titer as SAD-B19-{Delta}G can be prepared within a short time. Meanwhile, we found that N2cG coated CVS-N2c-{Delta}G allows efficient retrograde access to projection neurons, and further expand its application in VTA/SNc to DLS pathway that unaddressed by rAAV9-Retro, and the efficiency is 6 folds higher than that of rAAV9-Retro. Then the trans-synaptic efficiency of CVS-N2c-{Delta}G virus was evaluated. Results showed that the trans-mono-synaptic efficiency of oG-mediated CVS-N2c-{Delta}G was 2-3 folds higher than that of oG-mediated SAD-B19-{Delta}G, but there was no difference between oG-mediated and N2cG-mediated CVS-N2c-{Delta}G system. In addition, codon modified N2cG (optiG) did not increase the efficiency of CVS-N2c-{Delta}G tracing. Finally, we found that the CVS-N2c-{Delta}G produced by the improved method can be used for monitoring neural activity of projection neurons, and the time window can be maintained for 3 weeks, and it can also express sufficient recombinases for efficient transgene recombination. That is, the virus produced by the improved production system does not affect its own function, paving the way for its further optimization, popularization and application in structural and functional studies of neural circuits.

Embryonic exposure to valproic acid (VPA) and imidacloprid (IMI, a neonicotinoid insecticide) impairs filial imprinting in hatchlings, and the deteriorating effects of VPA are mitigated by post-hatch injection of bumetanide, a blocker of the chloride intruder NKCC1. Here, we report that these exposures depolarized the reversal potential of local GABAergic transmission in the neurons of the intermediate medial mesopallium (IMM), the pallial region critical for imprinting. Furthermore, exposure increased field excitatory post-synaptic potentials in pre-tetanus recordings (fEPSPs) and impaired long-term potentiation by low-frequency tetanic stimulation (LTP). Bath-applied bumetanide rescued the impaired LTP in the VPA slices, whereas VU0463271, a blocker of the chloride extruder KCC2, suppressed LTP in the control slices, suggesting that hyperpolarizing GABA action is necessary for the potentiation of excitatory synaptic transmission. However, the transcriptional profiles of IMM slices did not support the expected increase in the NKCC1/KCC2 ratio, suggesting a potential modification of post-transcriptional processes. Instead, exposure to both VPA and IMI downregulated several transcriptional regulators (FOS, NR4A1, and NR4A2) and upregulated the RNA component of signal recognition particles (RN7SL1). As a limited set of response genes were shared, VPA and IMI could cause common neuronal malfunctions via distinct molecular cascades.

The ability to track positions and poses (body parts) of multiple monkeys in a 3D space in real time is highly desired by non-human primate (NHP) researchers in behavioral and systems neuroscience because it allows both analyzing social behaviors among multiple NHPs and performing close-loop experiments (e.g., delivering sensory or optogenetics stimulation during a particular behavior). While a number of animal pose tracking systems have been reported, nearly all published work lacks the real-time analysis capacity. Existing methods for tracking freely moving animals have been developed primarily for rodents which typically move on a 2D space. In contrast, NHPs roam in a 3D space and move at a much faster speed than rodents. We have designed a real-time 3D pose tracking system (MarmoPose) based on deep learning to capture and quantify social behaviors in natural environment of a highly social NHP species, the common marmosets (Callithrix jacchus) which has risen to be an important NHP model in neuroscience research in recent years. This system has minimum hardware requirement and can accurately track the 3D poses (16 body locations) of multiple marmosets freely roaming in their homecage. It employs a marmoset skeleton model to optimize the 3D poses and estimate invisible body locations. Furthermore, it achieves high inference speed and provides an online processing module for real-time closed-loop experimental control based on the 3D poses of marmosets. While this system is optimized for marmosets, it can also be adapted for other large animal species in a typical housing environment with minimal modifications.

In honeybee society, a virgin queen usually mates only once with several drones before founding a colony. For the rest of her prolific life, she will not engage in subsequent mating events. In the Asian honeybee Apis cerana, the mechanisms controlling this reproductive strategy involves the queen-released mandibular pheromone (QMP). This pheromone blend regulates the physiology and reproductive behavior of workers and drones. Its main component, 9-oxo-(E)-2-decenoic acid (9-ODA), acts as a sex pheromone and attracts drones. However, how the QMP prevents additional mating later in the queens life remains elusive. Using behavioral and chemical analysis, we show that the QMP component methyl p-hydroxybenzoate (HOB) released by mated queens inhibits male attraction to 9-ODA. Furthermore, in vivo electroantennogram and single sensillum recording data indicated that HOB alone significantly reduces the spontaneous spike activity of 9-ODA-sensitive olfactory receptor neurons (ORNs). To explore the molecular mechanism underlying this inverse effect, we conducted qPCR and in situ hybridization assays. The results indicated that AcerOr11 is specifically expressed in sensilla placodea from the drones antennae, which are the sensilla that narrowly respond to both 9-ODA and HOB. We then cloned and expressed AcerOr11 in a Xenopus oocyte expression system, where AcerOr11 induced robust inward (regular) currents in response to 9-ODA. Intriguingly, HOB induced inverse currents in a dose-dependent manner. This suggests that HOB may act as an inverse agonist against AcerOr11, providing additional odor-coding information. Based on these findings, we propose a model in which AcerOr11 function as a dual modulators in regulating the mating behavior of A. cerana. The inverse agonist, HOB, can help manage the population dynamics of honeybees in apiculture.

In Drosophila melanogaster, olfactory projection neurons (PNs) convey odor information from the peripheral olfactory center to higher brain regions. The anatomical and physiological properties of PNs have been well characterized at the cellular and circuit level. The ultrastructural features of PNs remain unknown however, particularly with respect to presynaptic active zones (PAZs) and dense core vesicles (DCVs). In the current study, membrane-labeled electron microscopy was used to volume-reconstruct 89 PN axonal boutons and identify the internal PAZs and DCVs. Based on ultrastructural parameters, these PN boutons could be classified into three morphological distinct subtypes. Interestingly, the distributions of PAZs and DCVs were distinct within these three subtypes. DCVs were enriched in membrane labeled GH146-positive boutons, suggesting that GH146-positive PNs release both neurotransmitters and neuromodulators. The study identified the detailed distributions of PAZs and DCVs in PN boutons and indicates that neuromodulators mediated by DCVs may play an important role in PNs for olfactory processing.

The IR-mediated neuronal activation (IRNA) technology allows stimulation of neurons in the brain that heterologously-express members of the insect chemosensory IR repertoire in response to their cognate ligands. In the current protocol, a ligand against the complex consisting of IR84a and IR8a subunits, phenylacetic acid (PhAc), is locally injected into a brain region, because of a low efficiency of PhAc for the delivery into the brain across the blood-brain barrier. To circumvent this invasive injection, here we developed a strategy for activation of target neurons in the brain through peripheral administration with a precursor of PhAc, methyl ester of PhAc (PhAcM), which is efficiently transferred into the brain and converted to the mature ligand by endogenous esterase activities. Peripheral administration of with PhAcM activated IR84a/IR8a-expressing neurons in the locus coeruleus of mice and increased the release of neurotransmitters in their nerve terminal regions. (S)-2-phenylpropionic acid ((S)-PhPr) was newly identified as a ligand for IR84a/IR8a, and peripheral administration with the methyl ester of PhPr with the S-configuration [(S)-PhPrM] caused similar effects on the target neurons. In addition, cell-type specific expression of IR84a/IR8a complex in the striatum of rats was unilaterally induced with a viral vector based on the Cre-loxP system. Peripheral administration with PhAcM or (S)-PhPrM stimulated the neurotransmitter release in the ipsilateral terminal regions of the vector-injected striatum, and PhAcM administration resulted in rotational behavior. Finally, we demonstrated that the metabolites of the peripherally administered-radiolabeled (S)-PhPrM accumulated in the IR84a/IR8a-expressing region in the striatum of the vector-injected rats. These results demonstrate that the systemic IRNA technique provides a powerful strategy for remote manipulation of diverse types of target neurons in the mammalian central nervous system.

Escape responses, orienting reflexes, and social behaviors in Xenopus laevis tadpoles have been well documented in the literature (Lee et al. 2010; Roberts et al. 2000; Simmons et al. 2004; Katz et al. 1981; Villinger and Waldman 2012). In this article, we describe several behavioral protocols that together allow researchers efficiently (in terms of financial cost and time investment) and effectively assess developmental abnormalities in pre-metamorphic Xenopus tadpoles.

The nucleus accumbens (NAc) is a critical component of a limbic basal ganglia circuit that is thought to play an important role in decision-making and the processing of rewarding stimuli. As part of this circuit, dopamine D1 receptor-expressing medium spiny neurons (D1-MSNs) of the NAc core are known to send a major projection to the substantia nigra pars reticulata (SNr). However, the functional role of this SNr-projecting NAc D1-MSNs (NAcD1-MSN-SNr) pathway is still largely uncharacterized. Moreover, as the SNr is thought to belong to both limbic and motor information processing basal ganglia loops, it is possible that the NAcD1-MSN-SNr pathway may be able to influence both limbic and motor functions. In this study we investigated the effect of optogenetic activation of the NAcD1-MSN-SNr pathway on reward-learning and locomotor behavior. Stimulation of the axon terminals of NAc core D1-MSNs in the SNr induced a preference for a laser-paired location, self-stimulation via a laser-paired lever, and augmented instrumental responding for a liquid reward-paired lever. Additionally, stimulation was observed to increase locomotor behavior when delivered bilaterally and induced contralateral turning behavior when delivered unilaterally. These findings indicate that the NAcD1-MSN-SNr pathway is able to control both reward learning and motor behaviors.

Midbrain dopamine (DA) neurons are associated with locomotor and psychiatric disorders. DA subtype is specified in ancestral neural precursor cells (NPCs) and maintained throughout neuronal differentiation. Here we show that endogenous expression of MeCP2 coincides with DA subtype specification in mouse mesencephalon, and premature expression of MeCP2 prevents in vitro cultured NPCs from acquiring DA subtype through interfering NURR1 transactivation of DA phenotype genes. By contrast, MeCP2 overexpression does not disturb DA subtype in DA neurons. By analyzing the dynamic change of DNA methylation along DA neuronal differentiation at the promoter of DA phenotype gene tyrosine hydroxylase (Th), we show that Th expression is determined by TET1-mediated de-methylation of NURR1 binding sites within Th promoter. Chromatin immunoprecipitation assays demonstrate that MeCP2 dominates the DNA binding of the corresponding sites thereby blocking TET1 function in DA NPCs, whereas TET1-mediated de-methylation prevents excessive MeCP2 binding in DA neurons. The significance of temporal DNA methylation status is further confirmed by targeted methylation/demethylation experiments showing that targeted de-methylation in DA NPCs protects DA subtype specification from MeCP2 overexpression, whereas targeted methylation disturbs subtype maintenance in MeCP2-overexpressed DA neurons. These findings suggest the appropriate timing of MeCP2 expression as a novel determining factor for guiding NPCs into DA lineage.

Circadian rhythms play a crucial role in regulating behavior, physiology, and health. Sexual dimorphism, a widespread phenomenon across species, influences circadian behaviors. Additionally, post-mating physiological changes in females are known to modulate various behaviors, yet their effects on circadian rhythms remain underexplored. Here, using Drosophila melanogaster, a powerful model for studying circadian mechanisms, we systematically assessed the impact of sex and mating status on circadian behavior. We measured circadian period length and rhythm strength in virgin and mated males and females, including females mated to males lacking Sex Peptide (SP), a key mediator of post-mating changes. Across four wild-type and control strains, we found that males consistently exhibited shorter circadian periods than females, regardless of mating status, suggesting that circadian period length is a robust sexually dimorphic trait. In contrast, rhythm strength was influenced by the interaction between sex and mating status, with female mating generally reducing rhythm strength in the presence of SP signaling. Notably, genetic background significantly modulated these effects on rhythm strength. Our findings demonstrate that while circadian period length is a stable sex-specific trait, rhythm strength is shaped by a complex interplay between sex, mating status, and genetic background. This study advances our understanding of how sex and mating influence circadian rhythms in Drosophila and provides a foundation for future research into sexually dimorphic mechanisms underlying human diseases associated with circadian disruptions.

Pupils can signify various internal processes and states, such as attention, arousal, and working memory. Changes in pupil size have been associated with learning speed, prediction of future events, and deviations from the prediction in human studies. However, the detailed relationships between pupil size changes and prediction are unclear. We explored pupil size dynamics in mice performing a Pavlovian delay conditioning task. A head-fixed experimental setup combined with deep-learning-based image analysis enabled us to reduce spontaneous locomotor activity and to track the precise dynamics of pupil size of behaving mice. By setting up two experimental groups, one for which mice were able to predict reward in the Pavlovian delay conditioning task and the other for which mice were not, we demonstrated that the pupil size of mice is modulated by reward prediction and consumption, as well as body movements, but not by unpredicted reward delivery. Furthermore, we clarified that pupil size is still modulated by reward prediction even after the disruption of body movements by intraperitoneal injection of haloperidol, a dopamine D2 receptor antagonist. These results suggest that changes in pupil size reflect reward prediction signals. Thus, we provide important evidence to reconsider the neuronal circuit involved in computing reward prediction error. This integrative approach of behavioral analysis, image analysis, pupillometry, and pharmacological manipulation will pave the way for understanding the psychological and neurobiological mechanisms of reward prediction and the prediction errors essential to learning and behavior. Manuscript contributions to the fieldPredicting upcoming events is essential for the survival of many animals, including humans. Accumulating evidence suggests that pupillary responses reflect autonomic activity and are modulated by noradrenergic, cholinergic, and serotonergic neurotransmission. However, the relationships between pupillary responses, reward prediction, and reward prediction errors remain unclear. This study examined changes in pupil size while water-deprived mice performed a Pavlovian delay conditioning task using a head-fixed setup. The head-fixed experimental setup, combined with deep-learning-based image analysis, enabled us to reduce spontaneous locomotor activity and to track the precise dynamics of the licking response and the pupil size of behaving mice. A well-controlled, rigid behavioral experimental design allowed us to investigate the modulation of behavioral states induced by reward prediction. While pharmacological manipulation might affect pupil size, the combined approach of pupillometry and pharmacological manipulation allowed us to differentiate reward prediction signals and signals modulated by body movements. We revealed that the changes in pupil size (1) reflect reward prediction signals and (2) do not reflect signals of reward prediction error. These results provide novel insights into the neuronal circuitry potentially involved in computing reward prediction errors. The integrative approach of behavioral analysis, image analysis, pupillometry, and pharmacological manipulation used in this study will pave the way for understanding the psychological and neurobiological mechanisms of prediction and the prediction errors essential in learning and behavior.

In complex nervous systems, neurons must identify their correct partners to form synaptic connections. The prevailing model to ensure correct recognition posits that cell surface proteins (CSPs) in individual neurons act as identification tags. Thus, knowing what cells express which CSPs would provide insights into neural development, synaptic connectivity, and nervous system evolution. Here, we investigated expression of dprs and DIPs, two CSP subfamilies belonging to the immunoglobulin superfamily (IgSF), in Drosophila larval motor neurons (MNs), sensory neurons (SNs), peripheral glia and muscles using a collection of GAL4 driver lines. We found that dprs are more broadly expressed than DIPs in MNs and SNs, and each examined neuron expresses a unique combination of dprs and DIPs. Interestingly, many dprs and DIPs are not robustly expressed, but instead, are found in gradient and temporal expression patterns. Hierarchical clustering showed a similar expression pattern of dprs and DIPs in neurons from the same type and with shared synaptic partners, suggesting these CSPs may facilitate synaptic wiring. In addition, the unique expression patterns of dprs and DIPs revealed three uncharacterized MNs - MN23-Ib, MN6-Ib (A2) and MN7-Ib (A2). This study sets the stage for exploring the functions of dprs and DIPs in Drosophila MNs and SNs and provides genetic access to subsets of neurons.

Neuroanatomical tracing technology is fundamental for unraveling the complex network of brain connectome. Tracing tools that could spread between neurons are urgently needed, especially the rigorous trans-monosynaptic anterograde tracer is still lacking. HSV1 strain H129 was proved to be an anterograde tracer and has been used to trace neuronal networks in several reports. However, H129 has a serious defect that it was demonstrated to infect neurons via axon terminals. Thus, when using H129 to dissect output neural circuit, its terminal take up capacity should be carefully considered. Here, we report a recombinant H129 that carrying the anti-Her2 scFv in glycoprotein D to target genetically defined neurons. With the usage of helper virus complementarily expressing Her2 and gD, we can realize the elucidation of direct projection regions of either a given brain nucleus or a specific neuron type. The retargeted H129 system complements the current neural circuit tracer arsenal, which provides a rigorous and practical anterograde trans-monosynaptic tool.

ObjectiveThis study evaluated interpeak latency (IPL) and its inter-trial variability (VIL) of the electrically evoked compound action potential (eCAP) as potential alternatives to the phase-locking value (PLV) for quantifying cochlear nerve (CN) synchrony in cochlear implant (CI) users. DesignThe IPL was assessed in postlingually deafened adults and three pediatric populations: children with auditory neuropathy spectrum disorder, cochlear nerve deficiency, and typical sensorineural hearing loss. VIL was evaluated only in adults. Their associations with temporal resolution and speech perception outcomes were evaluated. Frequency analysis was conducted to understand the impacts of eCAP recording noise on IPL, VIL, and PLV. Simulations of inter-trial jitter in the eCAP were performed to quantify how the IPL, VIL, and PLV metrics varied with increased temporal jitter. ResultseCAP traces recorded in all patient groups showed a multi-peak issue affecting the accuracy of IPL and VIL assessments. Temporal resolution and speech perception outcomes were significantly correlated with VIL but not with IPL metrics. The PLV was impacted less by recording noise than either the IPL or the VIL. Simulation results revealed that the IPL was less sensitive to the amount of inter-trial jitter in the eCAP than were the VIL and the PLV. ConclusionsThe IPL is not a reliable indicator of CN synchrony. The VIL is indicative of neural synchrony in the CN but is affected more by the eCAP recording noise than the PLV. The PLV is therefore the preferred measure for quantifying neural synchrony in the CN in CI users. Statements and DeclarationsO_ST_ABSConflict of InterestC_ST_ABSNone. IRB informationThe data reported in this study were collected for the projects that were approved by the biomedical Institutional Review Board (IRB) of The Ohio State University (IRB study #: 2017H0131, 2018H0344 and 2018N0005; PI: Shuman He), and the IRB of the University of North Carolina at Chapel Hill (IRB study #: 12-1737; PI: Shuman He). Author ContributionsSH designed this study, participated in data analysis, drafted and approved the final version of this paper. ICB participated in study design and data analysis, conducted computational modeling work, drafted and approved the final version of this paper. ZG participated in data analysis, provided critical comments, and approved the final version of this paper. RAA participated in data analysis and approved the final version of this paper. CRM participated in data collection and approved the final version of this paper. Data Availability StatementThe data that support the findings of this study are available from the authors upon reasonable request with permissions from The Ohio State University and the University of North Carolina at Chapel Hill.

Pitch plays a fundamental role in prosody, lexical tone, and music perception, yet cochlear implant (CI) users exhibit limited temporal pitch sensitivity, particularly at higher pulse rates (e.g., 300 Hz). This study proposes a covarying pitch-encoding method, where the amplitude-modulation (AM) frequency and the pulse rate vary together in predetermined integer ratios to reinforce temporal periodicity cues. A single-channel psychophysical pitch discrimination experiment was conducted at the most apical electrode in 17 ears from 14 Cochlear CI users around reference frequencies of 50 and 300 Hz. The aims were to examine the effects of the integer ratio on pitch discrimination using the covarying method and to compare the performance of the covarying method with two conventional pitch encoding methods--pulse rate only and AM only. An additional consonant recognition task evaluated speech recognition ability. Results showed that at 50 Hz neither integer ratio nor pitch encoding method significantly affected pitch discrimination thresholds ({approx}30%). At 300 Hz, thresholds were overall higher than at 50 Hz, but the covarying method produced lower thresholds (41.8%) than the pulse rate (52.1%) and AM frequency methods (52.4%), and the covarying-pulse-rate difference was statistically significant. These results suggest that covarying stimulation can modestly enhance pitch discrimination at higher frequencies relative to conventional methods. Regression analyses revealed that temporal pitch discrimination in this psychophysical task at 50 Hz deteriorated with longer CI experience, whereas consonant recognition in a more ecologically relevant speech task improved, suggesting distinct neural adaptation mechanisms.

Sleep is a highly complex and conserved biological process that affects several body functions and behaviors. Recent evidence suggests that there is a reciprocal interaction between sleep and immunity. For instance, fragmented sleep can increase the probability of parasitic infections and reduce the ability of infected hosts to fight infections. It is also known, particularly in humans and other mammals, that viral and bacterial infections alter the sleep patterns of infected individuals. However, the effects of macro-parasitic infections on sleep remain largely unknown. In this study, we investigated whether macro-parasite infections could alter the sleep of their hosts. We experimentally infected three-spined sticklebacks (Gasterosteus aculeatus) with the tapeworm Schistocephalus solidus and used a hidden Markov model to characterize sleep-associated behaviors in the sticklebacks. At an early time-point, 1-4 days after parasite exposure, infected fish showed no difference in sleep compared with non-exposed fish, whereas fish that were exposed but could fend off the infection slept less during the daytime. At a later time-point, 29-32 days after exposure, infected fish slept more than uninfected fish, while exposed-but-not-infected fish slept less than non-exposed fish. Using RNA-seq of brain tissue, we identified several immune- and sleep-associated genes that potentially underlie the observed behavioral changes. These results provide the first insight into the complex association between macro-parasite infection, immunity, and sleep in fish and may thus contribute to a better understanding of the reciprocal interaction between sleep and immunity.