Biased embryos: Prenatal experience alters the postnatal malleability of auditory preferences in bobwhite quail

Impact of natural and artificial prenatal stimulations on the behavioural profile of Japanese quail

As the sensory systems of vertebrates develop prenatally, embryos perceive many environmental stimuli that can influence the ontogeny of their behaviour. Whether the nature and intensity of prenatal stimuli affect differently this ontogeny remains to be investigated. In this context, this study aimed to analyse the effects of prenatal auditory stimulations (natural stimulations "NS": predator vocalisations, or artificial stimulations "AS": metallic sounds) on the subsequent behaviour of young Japanese quail (Coturnix coturnix japonica). For that, behavioural variables recorded during ethological tests evaluating emotional and social reactivity were analysed using a principal component analysis. This analysis revealed significant differences between the behavioural profile of stimulated chicks and that of non-exposed chicks. Indeed, chicks exposed to NS expressed more intense emotional responses in fearful situations, but less neophobia in the presence of a novel environment or object, whereas chicks exposed to AS appeared more sensitive to social isolation. Our original results show that the acoustic environment of embryos can influence the way young birds subsequently interact with their social and physical environment after hatching, and face challenges in changing living conditions.

The duration of intrauterine development influences discrimination of speech prosody in infants

Auditory speech discrimination is essential for normal language development. Children born preterm are at greater risk of language developmental delays. Using functional near-infrared spectroscopy at term-equivalent age, the present study investigated early discrimination of speech prosody in 62 neonates born between week 23 and 41 of gestational age (GA). We found a significant positive correlation between GA at birth and neural discrimination of forward versus backward speech at term-equivalent age. Cluster analysis identified a critical threshold at around week 32 of GA, pointing out the existence of subgroups. Infants born before week 32 of GA exhibited a significantly different pattern of hemodynamic response to speech stimuli compared to infants born at or after week 32 of GA. Thus, children born before the GA of 32 weeks are especially vulnerable to early speech discrimination deficits. To support their early language development, we therefore suggest a close follow-up and additional speech and language therapy especially in the group of children born before week 32 of GA.

Hearing Better with the Right Eye? The Lateralization of Multisensory Processing Affects Auditory Learning in Northern Bobwhite Quail (Colinus Virginianus) Chicks

Precocial avian species exhibit a high degree of lateralization of perceptual and motor abilities, including preferential eye use for tasks such as social recognition and predator detection. Such lateralization has been related, in part, to differential experience prior to hatch. That is, due to spatial and resulting postural constraints late in incubation, one eye and hemisphere-generally the right eye / left hemisphere-receive greater amounts of stimulation than the contralateral eye / hemisphere. This raises the possibility that the left hemisphere may specialize or show relative advantages in integrating information across visual and auditory modalities, given that it typically receives greater amounts of multimodal auditory and visual stimulation prior to hatch. The present study represents an initial investigation of this question in a precocial avian species, the Northern bobwhite quail (Colinus virginianus). Day-old bobwhite chicks received 5 min training sessions in which they vocalized to receive contingent playback of a bobwhite maternal call, presented with or without a light that flashed in synchrony with the notes of the call (i.e., bimodal versus unimodal exposure, respectively). Chicks were trained with or without eye patches that allowed them to experience the visual component of the bimodal stimulus with only the left eye (LE), right eye (RE), or both eyes (i.e., binocular; BIN). Finally, the light was placed in various positions relative to the speakers playing the maternal call across three experiments. 24 hrs later chicks were provided a simultaneous choice test between the familiarized and a novel bobwhite maternal call. Given that the right eye and ear typically face outward and are thus unoccluded by the body during late prenatal development, we hypothesized that RE chicks would show facilitated learning under bimodal conditions compared to all other training conditions. This hypothesis was partially confirmed in Experiment 1, when the light was positioned 40 cm above the source of the maternal call. However, we also observed evidence of suppressed learning in chicks provided BIN exposure to the bimodal audio-visual stimulus that was not present during auditory-only training. Experiments 2 and 3 demonstrated that this was likely related to activation of a left-hemisphere dependent fear response when the left eye was exposed to a visual stimulus that loomed above the auditory stimulus. These results indicate that multisensory processing is lateralized in a precocial bird and that these species may thus provide a unique model for studying experience-dependent plasticity of intersensory perception.

The "Sound of Silence" in a Neonatal Intensive Care Unit-Listening to Speech and Music Inside an Incubator

Background: The intrauterine hearing experience differs from the extrauterine hearing exposure within a neonatal intensive care unit (NICU) setting. Also, the listening experience of a neonate drastically differs from that of an adult. Several studies have documented that the sound level within a NICU exceeds the recommended threshold by far, possibly related to hearing loss thereafter. The aim of this study was, first, to precisely define the dynamics of sounds within an incubator and, second, to give clinicians and caregivers an idea about what can be heard “inside the box.”

Methods: Audio recordings within an incubator were conducted at the Pediatric Simulation Center of the Medical University Vienna. They contained recorded music, speech, and synthesized sounds. To understand the dynamics of sounds around and within the incubator, the following stimuli were used: broadband noise with decreasing sound level in 10 steps of 6 dB, sine waves (62.5, 125, 250, 500, 1000, 2000, 4000, 8000, and 16,000 Hz), logarithmic sweep (Chirp) over the frequency band 20 Hz to 21 kHz, singing male voice, singing, and whispering female voice.

Results: Our results confirm a protective effect of the incubator from noises above 500 Hz in conditions of “no-flow” and show almost no protective effect of an incubator cover. We, furthermore, observed a strong boost of low frequencies below 125 Hz within the incubator, as well as a notable increase of higher frequency noises with open access doors, a significant resonant effect of the incubator, and a considerable masking effect of the respiratory support against any other source of noise or sound stimulation even for “low-flow” conditions.

Conclusion: Our study reveals high noise levels of air supply at high flow rates and the boost of low frequencies within the incubator. Education of medical staff and family members as well as modifications of the physical environment should aim at reducing noise exposure of preterm infants in the incubator. Audiovisual material is provided as Supplementary Material.

Absence of neural speech discrimination in preterm infants at term-equivalent age

Children born preterm are at higher risk to develop language deficits. Auditory speech discrimination deficits may be early signs for language developmental problems. The present study used functional near-infrared spectroscopy to investigate neural speech discrimination in 15 preterm infants at term-equivalent age compared to 15 full term neonates. The full term group revealed a significantly greater hemodynamic response to forward compared to backward speech within the left hemisphere extending from superior temporal to inferior parietal and middle and inferior frontal areas. In contrast, the preterm group did not show differences in their hemodynamic responses during forward versus backward speech, thus, they did not discriminate speech from non-speech. Groups differed significantly in their responses to forward speech, whereas they did not differ in their responses to backward speech. The significant differences between groups point to an altered development of the functional network underlying language acquisition in preterm infants as early as in term-equivalent age.

A difference in timing for the onset of visual and chemosensory systems during embryonic development in two closely related cuttlefish species

Embryos perceive environmental stimuli, thanks to their almost mature sensory systems. In cuttlefish, the embryonic development of Sepia officinalis and Sepia pharaonis is similar but the egg capsule transparency is different. S. officinalis' eggs are black (ink), which provide protection from predators. Conversely, those of S. pharaonis are translucent. The aim of this study was to test the visual and chemosensory perception abilities of these two cuttlefish embryos by observation of the ventilation rate (VR) before and after stimulation. Our results show that S. pharaonis responds to light at stage 22 and S. officinalis at stage 24. Conversely, S. pharaonis responds to predator odor at stage 23 and S. officinalis at stage 22. Both species are able to respond to these stimuli before hatching but do not have the same developmental schedule. Neither are the responses of the two cuttlefish exactly the same. In S. officinalis, VR increases after stimulations. In S. pharaonis, VR increases after light stimulation and decreases following the odor stimulation after stage 25. This result could reveal an ability to recognize stimuli at stage 25. The decrease could be identified as freezing-like behavior which would be more adaptive than an increase, since the embryos are visible.

The influence of prenatal experience on behavioral and social development: The benefits and limitations of an animal model

Prenatal experience is both a formative and a regulatory force in the process of development. As a result, birth is not an adequate starting point for explanations of behavioral development. However, surprisingly little is currently known regarding the role of prenatal experience in the emergence and facilitation of perceptual, cognitive, or social development. Our lack of knowledge in this area is due in part to the very restricted experimental manipulations possible with human fetuses. A comparative approach utilizing animal models provides an essential step in addressing this gap in our knowledge and providing testable predictions for studies with human fetuses, infants, and children. Further, animal-based comparative research serves to minimize the amount of exploratory research undertaken with human subjects and hone in on issues and research directions worthy of further research investment. In this article, I review selected animal-based research exploring how developmental influences during the prenatal period can guide and constrain subsequent behavioral and social development. I then discuss the importance of linking the prenatal environment to postnatal outcomes in terms of how psychologists conceptualize “innate” biases, preferences, and skills in the study of human development.

Song discrimination by nestling collared flycatchers during early development

Pre-zygotic isolation is often maintained by species-specific signals and preferences. However, in species where signals are learnt, as in songbirds, learning errors can lead to costly hybridization. Song discrimination expressed during early developmental stages may ensure selective learning later in life but can be difficult to demonstrate before behavioural responses are obvious. Here, we use a novel method, measuring changes in metabolic rate, to detect song perception and discrimination in collared flycatcher embryos and nestlings. We found that nestlings as early as 7 days old respond to song with increased metabolic rate, and, by 9 days old, have increased metabolic rate when listening to conspecific when compared with heterospecific song. This early discrimination between songs probably leads to fewer heterospecific matings, and thus higher fitness of collared flycatchers living in sympatry with closely related species.

The intersensory redundancy hypothesis: Extending the principle of unimodal facilitation to prenatal development

Selective attention to different properties of stimulation provides the foundation for perception, learning, and memory. The Intersensory Redundancy Hypothesis (IRH) proposes that early in development information presented redundantly across two or more modalities (multimodal) selectively recruits attention to and enhances perceptual learning of amodal properties, whereas information presented to a single sense modality (unimodal) enhances perceptual learning of modality-specific properties. The present study is the first to assess this principle of unimodal facilitation in non-human animals in prenatal development. We assessed bobwhite quail embryos' prenatal detection of pitch, a modality-specific property, under conditions of unimodal and bimodal (synchronous or asynchronous) exposure. Chicks exposed to prenatal unimodal auditory stimulation or asynchronous bimodal (audiovisual) stimulation preferred the familiarized maternal call over a novel pitch-modified maternal call following hatching, whereas chicks exposed to redundant (synchronous) audiovisual stimulation failed to prefer the familiar call over the pitch-modified call. These results provide further evidence that selective attention is recruited to specific stimulus properties of events in early development and that these biases are evident even during the prenatal period.

Prenatal environment affects embryonic response to song

Early environmental enrichment improves postnatal cognition in animals and humans. Here, we examined the effects of the prenatal acoustic environment (parental song rate) on prenatal attention in superb fairy-wren (Malurus cyaneus) embryos, the only songbird species with evidence of prenatal discrimination of maternal calls and in ovo call learning. Because both adults also sing throughout the incubation phase, we broadcast songs to embryos and measured their heart rate response in relation to parental song rate and tutor identity (familiarity, sex). Embryos from acoustically active families (high parental song rate) had the strongest response to songs. Embryos responded (i) strongest to male songs irrespective of familiarity with the singer, and (ii) strongest if their father had a high song rate during incubation. This is the first evidence for a prenatal physiological response to particular songs (potential tutors) in the egg, in relation to the prenatal acoustic environment, and before the sensitive period for song learning.

Elevated yolk progesterone moderates prenatal heart rate and postnatal auditory learning in bobwhite quail (Colinus virginianus)

Previous studies have established that yolk hormones of maternal origin can influence physiology and behavior in birds. However, few studies have examined the effects of maternal gestagens, like progesterone, on chick behavior and physiology. We tested the effects of experimentally elevated egg yolk progesterone on embryonic heart rate and postnatal auditory learning in bobwhite quail hatchlings. Quail chicks were passively exposed to an individual maternal assembly call for 10 min/hr during the 24 hr following hatching. Preference for the familiarized call was tested at 48 hr following hatching in three experimental groups: chicks that received artificially elevated yolk progesterone (P) prior to incubation, vehicle-only controls (V), and non-manipulated controls (C). Resting heart rate of P, V, and C embryos were also measured on prenatal day 17. The resting heart rate of P embryos was significantly higher than both the V and C embryos. Chicks from the P group also showed an enhanced preference for the familiarized bobwhite maternal call when compared to chicks from the C and V groups. Our results indicate that elevated yolk progesterone in pre-incubated bobwhite quail eggs can influence arousal level in bobwhite embryos and postnatal perceptual learning in bobwhite neonates.

A blueprint for vocal learning: auditory predispositions from brains to genomes

Memorizing and producing complex strings of sound are requirements for spoken human language. We share these behaviours with likely more than 4000 species of songbirds, making birds our primary model for studying the cognitive basis of vocal learning and, more generally, an important model for how memories are encoded in the brain. In songbirds, as in humans, the sounds that a juvenile learns later in life depend on auditory memories formed early in development. Experiments on a wide variety of songbird species suggest that the formation and lability of these auditory memories, in turn, depend on auditory predispositions that stimulate learning when a juvenile hears relevant, species-typical sounds. We review evidence that variation in key features of these auditory predispositions are determined by variation in genes underlying the development of the auditory system. We argue that increased investigation of the neuronal basis of auditory predispositions expressed early in life in combination with modern comparative genomic approaches may provide insights into the evolution of vocal learning.

Origins of Knowledge: Insights from Precocial Species

Behavioral responses are influenced by knowledge acquired during the lifetime of an individual and by predispositions transmitted across generations. Establishing the origin of knowledge and the role of the unlearned component is a challenging task, given that both learned and unlearned knowledge can orient perception, learning, and the encoding of environmental features since the first stages of life. Ethical and practical issues constrain the investigation of unlearned knowledge in altricial species, including human beings. On the contrary, precocial animals can be tested on a wide range of tasks and capabilities immediately after birth and in controlled rearing conditions. Insects and precocial avian species are very convenient models to dissect the knowledge systems that enable young individuals to cope with their environment in the absence of specific previous experience. We present the state of the art of research on the origins of knowledge that comes from different models and disciplines. Insects have been mainly used to investigate unlearned sensory preferences and prepared learning mechanisms. The relative simplicity of the neural system and fast life cycle of insects make them ideal models to investigate the neural circuitry and evolutionary dynamics of unlearned traits. Among avian species, chicks of the domestic fowl have been the focus of many studies, and showed to possess unlearned knowledge in the sensory, physical, spatial, numerical and social domains. Solid evidence shows the existence of unlearned knowledge in different domains in several species, from sensory and social preferences to the left-right representation of the mental number line. We show how non-mammalian models of cognition, and in particular precocial species, can shed light into the adaptive value and evolutionary history of unlearned knowledge.

Individual differences in behavioural plasticities

Interest in individual differences in animal behavioural plasticities has surged in recent years, but research in this area has been hampered by semantic confusion as different investigators use the same terms (e.g. plasticity, flexibility, responsiveness) to refer to different phenomena. The first goal of this review is to suggest a framework for categorizing the many different types of behavioural plasticities, describe examples of each, and indicate why using reversibility as a criterion for categorizing behavioural plasticities is problematic. This framework is then used to address a number of timely questions about individual differences in behavioural plasticities. One set of questions concerns the experimental designs that can be used to study individual differences in various types of behavioural plasticities. Although within-individual designs are the default option for empirical studies of many types of behavioural plasticities, in some situations (e.g. when experience at an early age affects the behaviour expressed at subsequent ages), 'replicate individual' designs can provide useful insights into individual differences in behavioural plasticities. To date, researchers using within-individual and replicate individual designs have documented individual differences in all of the major categories of behavioural plasticities described herein. Another important question is whether and how different types of behavioural plasticities are related to one another. Currently there is empirical evidence that many behavioural plasticities [e.g. contextual plasticity, learning rates, IIV (intra-individual variability), endogenous plasticities, ontogenetic plasticities) can themselves vary as a function of experiences earlier in life, that is, many types of behavioural plasticity are themselves developmentally plastic. These findings support the assumption that differences among individuals in prior experiences may contribute to individual differences in behavioural plasticities observed at a given age. Several authors have predicted correlations across individuals between different types of behavioural plasticities, i.e. that some individuals will be generally more plastic than others. However, empirical support for most of these predictions, including indirect evidence from studies of relationships between personality traits and plasticities, is currently sparse and equivocal. The final section of this review suggests how an appreciation of the similarities and differences between different types of behavioural plasticities may help theoreticians formulate testable models to explain the evolution of individual differences in behavioural plasticities and the evolutionary and ecological consequences of individual differences in behavioural plasticities.

Mother's voice and heartbeat sounds elicit auditory plasticity in the human brain before full gestation

Brain development is largely shaped by early sensory experience. However, it is currently unknown whether, how early, and to what extent the newborn's brain is shaped by exposure to maternal sounds when the brain is most sensitive to early life programming. The present study examined this question in 40 infants born extremely prematurely (between 25- and 32-wk gestation) in the first month of life. Newborns were randomized to receive auditory enrichment in the form of audio recordings of maternal sounds (including their mother's voice and heartbeat) or routine exposure to hospital environmental noise. The groups were otherwise medically and demographically comparable. Cranial ultrasonography measurements were obtained at 30 ± 3 d of life. Results show that newborns exposed to maternal sounds had a significantly larger auditory cortex (AC) bilaterally compared with control newborns receiving standard care. The magnitude of the right and left AC thickness was significantly correlated with gestational age but not with the duration of sound exposure. Measurements of head circumference and the widths of the frontal horn (FH) and the corpus callosum (CC) were not significantly different between the two groups. This study provides evidence for experience-dependent plasticity in the primary AC before the brain has reached full-term maturation. Our results demonstrate that despite the immaturity of the auditory pathways, the AC is more adaptive to maternal sounds than environmental noise. Further studies are needed to better understand the neural processes underlying this early brain plasticity and its functional implications for future hearing and language development.

Role of sound stimulation in reprogramming brain connectivity

Sensory stimulation has a critical role to play in the development of an individual. Environmental factors tend to modify the inputs received by the sensory pathway. The developing brain is most vulnerable to these alterations and interacts with the environment to modify its neural circuitry. In addition to other sensory stimuli, auditory stimulation can also act as external stimuli to provide enrichment during the perinatal period. There is evidence that suggests that enriched environment in the form of auditory stimulation can play a substantial role in modulating plasticity during the prenatal period. This review focuses on the emerging role of prenatal auditory stimulation in the development of higher brain functions such as learning and memory in birds and mammals. The molecular mechanisms of various changes in the hippocampus following sound stimulation to effect neurogenesis, learning and memory are described. Sound stimulation can also modify neural connectivity in the early postnatal life to enhance higher cognitive function or even repair the secondary damages in various neurological and psychiatric disorders. Thus, it becomes imperative to examine in detail the possible ameliorating effects of prenatal sound stimulation in existing animal models of various psychiatric disorders, such as autism.

Prenatal sensory experience affects hatching behavior in domestic chicks (Gallus gallus) and Japanese quail chicks (Coturnix coturnix japonica)

Species-typical developmental outcomes result from organismic and environmental constraints and experiences shared by members of a species. We examined the effects of enhanced prenatal sensory experience on hatching behaviors by exposing domestic chicks (n = 95) and Japanese quail (n = 125) to one of four prenatal conditions: enhanced visual stimulation, enhanced auditory stimulation, enhanced auditory and visual stimulation, or no enhanced sensory experience (control condition). In general, across species, control embryos had slower hatching behaviors than all other embryos. Embryos in the auditory condition had faster hatching behaviors than embryos in the visual and control conditions. Auditory-visual condition embryos showed similarities to embryos exposed to either auditory or visual stimulation. These results suggest that prenatal sensory experience can influence hatching behavior of precocial birds, with the type of stimulation being a critical variable. These results also provide further evidence that species-typical outcomes are the result of species-typical prenatal experiences.

The origins of variation: evolutionary insights from developmental science

Evidence from contemporary epigenetic research indicates that it is not biologically meaningful to discuss genes without reference to the molecular, cellular, organismal, and environmental context within which they are activated and expressed. Genetic and nongenetic factors, including those beyond the organism, constitute a dynamic relational developmental system. This insight highlights the importance of bringing together genetics, development, and ecology into one explanatory framework for a more complete understanding of the emergence and maintenance of phenotypic stability and variability. In this Chapter, I review some examples of this integrative effort and explore its implications for developmental and evolutionary science, with a particular emphasis on the origins of phenotypic novelty. I argue that developmental science is critical to this integrative effort, in that evolutionary explanation cannot be complete without developmental explanation. This is the case because the process of development generates the phenotypic variation on which natural selection can act.

Processing of communication sounds: contributions of learning, memory, and experience

Abundant evidence from both field and lab studies has established that conspecific vocalizations (CVs) are of critical ecological significance for a wide variety of species, including humans, non-human primates, rodents, and other mammals and birds. Correspondingly, a number of experiments have demonstrated behavioral processing advantages for CVs, such as in discrimination and memory tasks. Further, a wide range of experiments have described brain regions in many species that appear to be specialized for processing CVs. For example, several neural regions have been described in both mammals and birds wherein greater neural responses are elicited by CVs than by comparison stimuli such as heterospecific vocalizations, nonvocal complex sounds, and artificial stimuli. These observations raise the question of whether these regions reflect domain-specific neural mechanisms dedicated to processing CVs, or alternatively, if these regions reflect domain-general neural mechanisms for representing complex sounds of learned significance. Inasmuch as CVs can be viewed as complex combinations of basic spectrotemporal features, the plausibility of the latter position is supported by a large body of literature describing modulated cortical and subcortical representation of a variety of acoustic features that have been experimentally associated with stimuli of natural behavioral significance (such as food rewards). Herein, we review a relatively small body of existing literature describing the roles of experience, learning, and memory in the emergence of species-typical neural representations of CVs and auditory system plasticity. In both songbirds and mammals, manipulations of auditory experience as well as specific learning paradigms are shown to modulate neural responses evoked by CVs, either in terms of overall firing rate or temporal firing patterns. In some cases, CV-sensitive neural regions gradually acquire representation of non-CV stimuli with which subjects have training and experience. These results parallel literature in humans describing modulation of responses in face-sensitive neural regions through learning and experience. Thus, although many questions remain, the available evidence is consistent with the notion that CVs may acquire distinct neural representation through domain-general mechanisms for representing complex auditory objects that are of learned importance to the animal. This article is part of a Special Issue entitled "Communication Sounds and the Brain: New Directions and Perspectives".

Prenatal chemosensory learning by the predatory mite Neoseiulus californicus

Background

Prenatal or embryonic learning, behavioral change following experience made prior to birth, may have significant consequences for postnatal foraging behavior in a wide variety of animals, including mammals, birds, fish, amphibians, and molluscs. However, prenatal learning has not been previously shown in arthropods such as insects, spiders and mites.

Methodology/Principal Findings

We examined prenatal chemosensory learning in the plant-inhabiting predatory mite Neoseiulus californicus. We exposed these predators in the embryonic stage to two flavors (vanillin or anisaldehyde) or no flavor (neutral) by feeding their mothers on spider mite prey enriched with these flavors or not enriched with any flavor (neutral). After the predators reached the protonymphal stage, we assessed their prey choice through residence and feeding preferences in experiments, in which they were offered spider mites matching the maternal diet (neutral, vanillin or anisaldehyde spider mites) and non-matching spider mites. Predator protonymphs preferentially resided in the vicinity of spider mites matching the maternal diet irrespective of the type of maternal diet and choice situation. Across treatments, the protonymphs preferentially fed on spider mites matching the maternal diet. Prey and predator sizes did not differ among neutral, vanillin and anisaldehyde treatments, excluding the hypothesis that size-assortative predation influenced the outcome of the experiments.

Conclusions/Significance

Our study reports the first example of prenatal learning in arthropods.