Research on visually driven behavior in anurans has often focused on Dendrobatoidea, a clade with extensive variation in skin reflectance, which is perceived to range from cryptic to conspicuous coloration. Because these skin patterns are important in intraspecific and interspecific communication, we hypothesized that the visual spectral sensitivity of dendrobatids should vary with conspecific skin spectrum. We predicted that the physiological response of frog retinas would be tuned to portions of the visible light spectrum that match their body reflectance. Using wavelength-specific electroretinograms (ERGs; from 350-650 nm), spectrometer measurements, and color-calibrated photography of the skin, we compared retinal sensitivity and reflectance of two cryptic species (Allobates talamancae and Silverstoneia flotator), two intermediate species (Colostethus panamansis and Phyllobates lugubris), and two conspicuous aposematic species (Dendrobates tinctorius and Oophaga pumilio). Consistent with the matched filter hypothesis, the retinae of cryptic and intermediate species were sensitive across the spectrum, without evidence of spectral tuning to specific wavelengths, yielding low-threshold broadband sensitivity. In contrast, spectral tuning was found to be different between morphologically distinct populations of O. pumilio, where frogs exhibited retinal sensitivity better matching their morph’s reflectance. This sensory specialization is particularly interesting given the rapid phenotypic divergence exhibited by this species and their behavioral preference for sympatric skin reflectances. Overall, this study suggests that retinal sensitivity is coevolving with reflective strategy and spectral reflectance in dendrobatids.

For complex communication signals, it is often difficult to identify the information-bearing elements and their parameters necessary to elicit functional behavior. Consequently, it may be difficult to design stimuli that test how neurons contribute to communicative processing. For túngara frogs (Physalaemus pustulosus), however, previous behavioral testing with numerous stimuli showed that a particular frequency modulated (FM) transition in the male call is required to elicit phonotaxis and vocal responses. Modeled on such behavioral experiments, we used awake in vivo recordings of single units in the midbrain to determine if their excitation was biased to behaviorally important FM parameters. Comparisons of stimulus driven action potentials revealed greatest excitation to the behaviorally important FM transition: a downward FM sweep or step that crosses ~600 Hz. Previous studies using long-duration acoustic exposure found immediate early gene expression in many midbrain neurons to be most sensitive to similar FM. However, those data could not determine if FM coding was accomplished by the population and/or individual neurons. Our data suggest both coding schemes could operate, as 1) individual neurons are more sensitive to the behaviorally significant FM transition and 2) when single unit recordings are analytically combined across cells, the combined code can produce high stimulus discrimination (FM vs. noise driven excitation), approaching that found in behavioral discrimination of call vs. noise.

Although mate searching behavior in female túngara frogs (Physalaemus pustulosus) is nocturnal and largely mediated by acoustic cues, male signaling includes visual cues produced by the vocal sac. To compensate for these low light conditions, visual sensitivity in females is modulated when they are in a reproductive state, as retinal thresholds are decreased. This study tested whether estradiol (E2) plays a role in this modulation. Female túngara frogs were injected with either human chorionic gonadotropin (hCG) or a combination of hCG and fadrozole. hCG induces a reproductive state and increases retinal sensitivity, while fadrozole is an aromatase inhibitor that blocks hCG-induced E2 synthesis. In an analysis of scotopic electroretinograms (ERGs), hCG treatment lowered the threshold for eliciting a b-wave response, whereas the addition of fadrozole abolished this effect, matching thresholds in non-reproductive saline-injected controls. This suggests that blocking E2 synthesis blocked the hCG-mediated reproductive modulation of retinal sensitivity. By implicating E2 in control of retinal sensitivity, our data add to growing evidence that the targets of gonadal steroid feedback loops include sensory receptor organs, where stimulus sensitivity may be modulated, rather than more central brain nuclei, where modulation may affect mechanisms involved in motivation.

Visual cues are often a vital part of animal communication and courtship. While a plethora of studies have focused on the role that hormones play in acoustic communication of anurans, relatively few have explored hormonal modulation of vision in these animals. Much of what we do know comes from behavioral studies, which show that a frog’s hormonal state can significantly affect both its visual behavior and mating decisions. However, to fully understand how frogs use visual cues to make these mating decisions, we must first understand how their visual system processes these cues, and how hormones affect these processes. To do this, we performed electroretinograms (ERGs) to measure retinal sensitivity of túngara frogs (Physalaemus pustulosus), a neotropical species whose mating behavior includes previously described visual cues. To determine the effect of hormonal state on visual sensitivity, ERGs were recorded under scotopic and photopic conditions in frogs that were either non-reproductive or hormone-treated with human chorionic gonadotropin (hCG) prior to testing. Additionally, measurements of optical anatomy determined how túngara frog eye and retina morphology related to physiological sensitivity. As expected, we found that both sexes display higher visual sensitivity under scotopic conditions compared to photopic conditions. However, hormone injections significantly increased retinal sensitivity of females under scotopic conditions. These results support the hypothesis that hormonal modulation of neural mechanisms, such as those mediating visually guided reproductive behavior in this species, include modulation of the receptor organ: the retina. Thus, our data serve as a starting point for elucidating the mechanism of hormonal modulation of visual sensitivity.

Usher syndrome is a syndromic form of hereditary hearing impairment that includes sensorineural hearing loss and delayed-onset retinitis pigmentosa (RP). Type 1 Usher syndrome (USH1) is characterized by congenital profound sensorineural hearing impairment and vestibular areflexia, with adolescent-onset RP. Systemic treatment with antisense oligonucleotides (ASOs) targeting the human USH1C c.216G>A splicing mutation in a knockin mouse model of USH1 restores hearing and balance. Herein, we explore the effect of delivering ASOs locally to the ear to treat hearing and vestibular dysfunction associated with Usher syndrome. Three localized delivery strategies were investigated in USH1C mice: inner ear injection, trans-tympanic membrane injection, and topical tympanic membrane application. We demonstrate, for the first time, that ASOs delivered directly to the ear correct Ush1c expression in inner ear tissue, improve cochlear hair cell transduction currents, restore vestibular afferent irregularity, spontaneous firing rate, and sensitivity to head rotation, and successfully recover hearing thresholds and balance behaviors in USH1C mice. We conclude that local delivery of ASOs to the middle and inner ear reach hair cells and can rescue both hearing and balance. These results also demonstrate the therapeutic potential of ASOs to treat hearing and balance deficits associated with Usher syndrome and other ear diseases.

The absence of functional outer hair cells is a component of several forms of hereditary hearing impairment, including Usher syndrome, the most common cause of concurrent hearing and vision loss. Antisense oligonucleotide (ASO) treatment of mice with the human Usher mutation, Ush1c c.216G>A, corrects gene expression and significantly improves hearing, as measured by auditory-evoked brainstem responses (ABRs), as well as inner and outer hair cell (IHC and OHC) bundle morphology. However, it is not clear whether the improvement in hearing achieved by ASO treatment involves the functional rescue of outer hair cells. Here, we show that Ush1c c.216AA mice lack OHC function as evidenced by the absence of distortion product otoacoustic emissions (DPOAEs) in response to low-, mid-, and high-frequency tone pairs. This OHC deficit is rescued by treatment with an ASO that corrects expression of Ush1c c.216G>A. Interestingly, although rescue of inner hairs cells, as measured by ABR, is achieved by ASO treatment as late as 7 days after birth, rescue of outer hair cells, measured by DPOAE, requires treatment before post-natal day 5. These results suggest that ASO-mediated rescue of both IHC and OHC function is age dependent and that the treatment window is different for the different cell types. The timing of treatment for congenital hearing disorders is of critical importance for the development of drugs such ASO-29 for hearing rescue.

Light intensity varies 1 million‐fold between night and day, driving the evolution of eye morphology and retinal physiology. Despite extensive research across taxa showing anatomical adaptations to light niches, surprisingly few empirical studies have quantified the relationship between such traits and the physiological sensitivity to light. In this study, we employ a comparative approach in frogs to determine the physiological sensitivity of eyes in two nocturnal (Rana pipiens, Hyla cinerea) and two diurnal species (Oophaga pumilio, Mantella viridis), examining whether differences in retinal thresholds can be explained by ocular and cellular anatomy. Scotopic electroretinogram (ERG) analysis of relative b‐wave amplitude reveals 10‐ to 100‐fold greater light sensitivity in nocturnal compared to diurnal frogs. Ocular and cellular optics (aperture, focal length, and rod outer segment dimensions) were assessed via the Land equation to quantify differences in optical sensitivity. Variance in retinal thresholds was overwhelmingly explained by Land equation solutions, which describe the optical sensitivity of single rods. Thus, at the b‐wave, stimulus‐response thresholds may be unaffected by photoreceptor convergence (which create larger, combined collecting areas). Follow‐up experiments were conducted using photopic ERGs, which reflect cone vision. Under these conditions, the relative difference in thresholds was reversed, such that diurnal species were more sensitive than nocturnal species. Thus, photopic data suggest that rod‐specific adaptations, not ocular anatomy (e.g., aperture and focal distance), drive scotopic thresholds differences. To the best of our knowledge, these data provide the first quantified relationship between optical and physiological sensitivity in vertebrates active in different light regimes.

Bats choose flowers on the basis of nectar volume and concentration, affecting how the flowers evolve

Perceptually, grouping sounds based on their sources is critical for communication. This is especially true in túngara frog breeding aggregations, where multiple males produce overlapping calls that consist of an FM 'whine' followed by harmonic bursts called 'chucks'. Phonotactic females use at least two cues to group whines and chucks: whine-chuck spatial separation and sequence. Spatial separation is a primitive cue, whereas sequence is schema-based, as chuck production is morphologically constrained to follow whines, meaning that males cannot produce the components simultaneously. When one cue is available, females perceptually group whines and chucks using relative comparisons: components with the smallest spatial separation or those closest to the natural sequence are more likely grouped. By simultaneously varying the temporal sequence and spatial separation of a single whine and two chucks, this study measured between-cue perceptual weighting during a specific grouping task. Results show that whine-chuck spatial separation is a stronger grouping cue than temporal sequence, as grouping is more likely for stimuli with smaller spatial separation and non-natural sequence than those with larger spatial separation and natural sequence. Compared to the schema-based whine-chuck sequence, we propose that spatial cues have less variance, potentially explaining their preferred use when grouping during directional behavioral responses.

A critical component of communication in humans and nonhuman animals is the ability to group signals so that they can be assigned to their correct sources. This is especially true for mate choice behavior, as incorrect stimulus grouping could lead to inaccurate evaluation of signalers by receivers, ultimately resulting in costly mate choice decisions. Sexual signals are often complex, consisting of components that vary in several physical parameters and across sensory modalities. Thus, the mate choice behavior of receivers is well suited for psychophysical tests of the limits and mechanisms of perceptual grouping both within and across sensory modalities. This chapter examines perceptual grouping in comparative models of mate choice behavior. We focus primarily on mate attraction in frogs, reviewing first the effects of spectral, temporal, and spatial parameters on sequential and simultaneous auditory grouping. We then review research on cross-modal perceptual grouping of frog visual and acoustic signals, a perceptual ability analogous to that of grouping human speech with its coincident mouth movements. In addition, we suggest that data from comparative models are not only useful for understanding signal processing in animal communication but also for potentially understanding the fundamental mechanisms receivers use to sort complex signals across all taxa and how such mechanisms may evolve.

The purpose of this study was to evaluate short and long‐term effects of adding a brain dissection activity to a medical neuroscience course. First‐year medical students participated in a brain dissection activity that included dissection of the basal nuclei and associated deep brain structures. Short‐term retention was assessed by administering identical pre and post‐activity tests involving identification of brain structures. The assessment consisted of items that were included in the brain dissection protocol (deep structures), and also items that were not part of the dissection protocol (superficial structures). Following the brain dissection, the students' ability to identify deep brain structures increased significantly (mean score: 72.0%±20.8%), while their ability to identify superficial structures remained the same (64.25%±16.25%). Long‐ term retention was evaluated by conducting an identical assessment five months after completion of the course. Students who participated in the dissection activity (n= 81) had significantly higher scores (49.31%± 20.6%) than the students who did not participate in the dissection activity (n=86) (40.5%± 19.2%) (p 蠄 0.01). In addition to the long‐term retention assessment, the NMBE subject examination scores of students who participated in the dissection activity were significantly higher than the students who did not participate in the dissection activity (p 蠄 0.01). A short brain dissection activity may improve students' ability to learn neuroanatomy. This effect may have long‐term benefits on knowledge retention and may be correlated with performance level on standardized subject exams.

Descending circuitry can modulate auditory processing, biasing sensitivity to particular stimulus parameters and locations. Using awake in vivo single unit recordings, this study tested whether electrical stimulation of the thalamus modulates auditory excitability and relative binaural sensitivity in neurons of the amphibian midbrain. In addition, by using electrical stimuli that were either longer than the acoustic stimuli (i.e., seconds) or presented on a sound-by-sound basis (ms), experiments addressed whether the form of modulation depended on the temporal structure of the electrical stimulus. Following long duration electrical stimulation (3-10 s of 20 Hz square pulses), excitability (spikes/acoustic stimulus) to free-field noise stimuli decreased by 32%, but returned over 600 s. In contrast, sound-by-sound electrical stimulation using a single 2 ms duration electrical pulse 25 ms before each noise stimulus caused faster and varied forms of modulation: modulation lasted <2 s and, in different cells, excitability either decreased, increased or shifted in latency. Within cells, the modulatory effect of sound-by-sound electrical stimulation varied between different acoustic stimuli, including for different male calls, suggesting modulation is specific to certain stimulus attributes. For binaural units, modulation depended on the ear of input, as sound-by-sound electrical stimulation preceding dichotic acoustic stimulation caused asymmetric modulatory effects: sensitivity shifted for sounds at only one ear, or by different relative amounts for both ears. This caused a change in the relative difference in binaural sensitivity. Thus, sound-by-sound electrical stimulation revealed fast and ear-specific (i.e., lateralized) auditory modulation that is potentially suited to shifts in auditory attention during sound segregation in the auditory scene.

Hearing impairment is the most common sensory disorder, with congenital hearing impairment present in approximately 1 in 1,000 newborns. Hereditary deafness is often mediated by the improper development or degeneration of cochlear hair cells. Until now, it was not known whether such congenital failures could be mitigated by therapeutic intervention. Here we show that hearing and vestibular function can be rescued in a mouse model of human hereditary deafness. An antisense oligonucleotide (ASO) was used to correct defective pre-mRNA splicing of transcripts from the USH1C gene with the c.216G>A mutation, which causes human Usher syndrome, the leading genetic cause of combined deafness and blindness. Treatment of neonatal mice with a single systemic dose of ASO partially corrects Ush1c c.216G>A splicing, increases protein expression, improves stereocilia organization in the cochlea, and rescues cochlear hair cells, vestibular function and low-frequency hearing in mice. These effects were sustained for several months, providing evidence that congenital deafness can be effectively overcome by treatment early in development to correct gene expression and demonstrating the therapeutic potential of ASOs in the treatment of deafness.

Studies of patterned spontaneous activity can elucidate how the organization of neural circuits emerges. Using in vivo two-photon Ca(2+) imaging, we studied spatio-temporal patterns of spontaneous activity in the optic tectum of Xenopus tadpoles. We found rhythmic patterns of global synchronous spontaneous activity between neurons, which depends on visual experience and developmental stage. By contrast, synchronous spontaneous activity between non-neuronal cells is mediated more locally. To understand the source of the neuronal spontaneous activity, input to the tectum was systematically removed. Whereas removing input from the visual or mechanosensory system alone had little effect on patterned spontaneous activity, removing input from both systems drastically altered it. These results suggest that either input is sufficient to maintain the intrinsically generated spontaneous activity and that patterned spontaneous activity results from input from multisensory systems. Thus, the amphibian midbrain differs from the mammalian visual system, whose spontaneous activity is controlled by retinal waves.

The mating calls of male túngara frogs, Physalaemus pustulosus , attract intended (conspecific females) and unintended (eavesdropping predators and parasites) receivers. The calls are complex, having two components: a frequency-modulated “whine” followed by 0–7 harmonic bursts or “chucks”. The whine is necessary and sufficient to elicit phonotaxis from females and the chuck enhances call attractiveness when it follows a whine. Although chucks are never made alone, females perceptually bind the whine and chuck when they are spatially separated. We tested whether an unintended receiver with independent evolution of phonotaxis, the frog-eating bat, Trachops cirrhosus , has converged with frogs in its auditory grouping of the call components. In contrast to frogs, bats approached chucks broadcast alone; when the chuck was spatially separated from the whine the bats preferentially approached the whine, and bats were sensitive to whine–chuck temporal sequence. This contrast suggests that although disparate taxa may be selected to respond to the same signals, different evolutionary histories, selective regimes, and neural and cognitive architectures may result in different weighting and grouping of signal components between generalist predators and conspecific mates.

Neural adaptation, a reduction in the response to a maintained stimulus, is an important mechanism for detecting stimulus change. Contributing to change detection is the fact that adaptation is often stimulus specific: adaptation to a particular stimulus reduces excitability to a specific subset of stimuli, while the ability to respond to other stimuli is unaffected. Phasic cells (e.g., cells responding to stimulus onset) are good candidates for detecting the most rapid changes in natural auditory scenes, as they exhibit fast and complete adaptation to an initial stimulus presentation. We made recordings of single phasic auditory units in the frog midbrain to determine if adaptation was specific to stimulus frequency and ear of input. In response to an instantaneous frequency step in a tone, 28 % of phasic cells exhibited frequency specific adaptation based on a relative frequency change (delta-f = ±16 %). Frequency specific adaptation was not limited to frequency steps, however, as adaptation was also overcome during continuous frequency modulated stimuli and in response to spectral transients interrupting tones. The results suggest that adaptation is separated for peripheral (e.g., frequency) channels. This was tested directly using dichotic stimuli. In 45 % of binaural phasic units, adaptation was ear specific: adaptation to stimulation of one ear did not affect responses to stimulation of the other ear. Thus, adaptation exhibited specificity for stimulus frequency and lateralization at the level of the midbrain. This mechanism could be employed to detect rapid stimulus change within and between sound sources in complex acoustic environments.