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Severe feather pecking (SFP) in chickens is a detrimental behaviour with possibly neurochemical deficits at its base. Recent neurological studies depicted conflicting results on the role of serotonin (5-hydroxytryptamine, 5-HT) and dopamine (DA) in the development and display of feather pecking. We studied brain monoamine levels and behaviour in domestic chickens divergently genetically selected on feather pecking behaviour, the Low Feather Pecking (LFP) and High Feather Pecking (HFP) lines, both at a young age and when adult, to elucidate the role of 5-HT and DA in feather pecking. Also pecking behaviour and the behavioural response to challenging test situations was determined. At 8 weeks of age, HFP had lower 5-HT and DA turnover in several brain areas than LFP, whereas these differences had disappeared or were even reversed at 25 weeks of age. Line differences in central monoamine activity were found both in emotion-regulating and motor-regulating areas. As expected from previous generations, HFP exceeded LFP in most types of pecking at other birds, including severe feather pecking. Furthermore, HFP responded more actively in most behavioural tests conducted, and seem more impulsive or (hyper)active in their way of coping with challenges. This paper shows different developmental trajectories of the neurochemical systems (5-HT and DA) for chickens divergently selected on feather pecking behaviour, and a remarkable reversion of differences in monoamine activity at a later stage of life. Whether this is a cause or consequence of SFP needs further investigation.

The perception of danger in the environment can induce physiological responses (such as a heightened state of arousal) in animals, which may cause measurable changes in the prosodic modulation of the voice (Briefer, 2012). The ability to interpret the prosodic features of animal calls as an indicator of emotional arousal may have provided the first hominins with an adaptive advantage, enabling, for instance, the recognition of a threat in the surroundings. This ability might have paved the ability to process meaningful prosodic modulations in the emerging linguistic utterances. Research has shown that humans are able to recognize different levels of arousal in mammalian calls. However, to our knowledge, no study has ever examined humans’ cross-cultural ability to identify different arousal levels in calls of species belonging to several phyologenetically distant taxa, including, for instance, mammals and birds. We addressed this issue by developing a task in which human participants of three different cultures (Canadian, German, Mandarin) listened to ten pairs of vocalizations for each of nine different vertebrate taxa. We used amplitude-controlled calls from the following species: hourglass treefrog, American alligator, black-capped chickadee, common raven, domestic pig, giant panda, African elephant, Barbary macaque, and human. Calls within each pair differed in arousal level, which was assessed based on the behavioral context of call production (Avey et al., 2011; Bowling et al., 2012; Fischer et al. 1995; Linhart et al., 2015; Reichert 2013; Stoeger et al., 2011, 2012). For each pair of vocalizations, participants were asked to identify the call with the higher level of arousal. Accuracy rate in identifying arousal in each species was higher than expected by chance in all three cultures. No significant differences were observed between cultures. This finding provides empirical support for Darwin’s hypothesis on the universality of vocal emotional communication. In order to better understand the mechanisms underlying emotional intensity recognition in our set of calls, we investigated which acoustic parameters correlate with participants’ correct responses. We performed this analysis in two steps. First, we identified two acoustic features measurable in all calls of our stimuli set: duration and a frequency related measure, the spectral center of gravity. Second, we calculated the duration and the spectral center of gravity ratio for each pair of calls and correlated these two feature comparisons with the percentage of correct responses across pairs. Our data indicate that the spectral center of gravity is the only feature found across our animal species calls, which significantly correlates with the ability to discriminate high arousal calls. Further work within this research paradigm will provide quantitative data on shared mechanisms involved in emotional vocalizations’ production and perception across animal taxa, investigating the perception of arousal in nonhuman species. This may improve our understanding of the semantic value of prosody in animal communication, and of its role in the emergence of human language. References Avey, M. T., Hoeschele, M., Moscicki, M. K., Bloomfield, L. L., & Sturdy, C. B. (2011). Neural correlates of threat perception: neural equivalence of conspecific and heterospecific mobbing calls is learned. PloS one, 6, e23844. Bowling, D. L., Sundararajan, J., Han, S. E., & Purves, D. (2012). Expression of emotion in Eastern and Western music mirrors vocalization. PLoS One, 7, e3194. Briefer, E. F. (2012). Vocal expression of emotions in mammals: mechanisms of production and evidence. Journal of Zoology, 288, 1-20. Fischer, J., Hammerschmidt, K., & Todt, D. (1995). Factors affecting acoustic variation in Barbary‐macaque (Macaca sylvanus) Disturbance Calls. Ethology, 101, 51-66. Linhart, P., Ratcliffe, V. F., Reby, D., & Špinka, M. (2015). Expression of Emotional Arousal in Two Different Piglet Call Types. PloS one, 10(8), e0135414. Reichert, M. S. (2013). Sources of variability in advertisement and aggressive calling in competitive interactions in the grey treefrog, Hyla versicolor.Bioacoustics, 22, 195-214. Stoeger, A. S., Charlton, B. D., Kratochvil, H., & Fitch, W. T. (2011). Vocal cues indicate level of arousal in infant African elephant roars. The Journal of the Acoustical Society of America, 130(3), 1700-1710. Stoeger, A. S., Baotic, A., Li, D., & Charlton, B. D. (2012). Acoustic features indicate arousal in infant giant panda vocalisations. Ethology, 118(9), 896-905.

Pigeons are well known for their visual capabilities as well as their ability to categorize visual stimuli at both the basic and superordinate level. We adopt a reverse engineering approach to study categorization learning: Instead of training pigeons on predefined categories, we simply present stimuli and analyze neural output in search of categorical clustering on a solely neural level. We presented artificial stimuli, pictorial and grating stimuli, to pigeons without the need of any differential behavioral responding while recording from the nidopallium frontolaterale (NFL), a higher visual area in the avian brain. The pictorial stimuli differed in color and shape; the gratings differed in spatial frequency and amplitude. We computed representational dissimilarity matrices to reveal categorical clustering based on both neural data and pecking behavior. Based on neural output of the NFL, pictorial and grating stimuli were differentially represented in the brain. Pecking behavior showed a similar pattern, but to a lesser extent. A further subclustering within pictorial stimuli according to color and shape, and within gratings according to frequency and amplitude, was not present. Our study gives proof-of-concept that this reverse engineering approach-namely reading out categorical information from neural data--can be quite helpful in understanding the neural underpinnings of categorization learning.

The dopaminergic (DA) innervation of the caudal telencephalon of the pigeon was investigated with an antiserum against glutaraldehylde-conjugated dopamine. It was found that the DA-like fibers were distributed within the Paleostriatum augmentatum and the dorsal Archistriatum in a dense meshwork of fibers, while most of the remaining part of the caudal forebrain was innervated by dopaminergic axons which were coiled up like baskets around unlabelled neurons. Within the basket-type innervated structures, the Neostriatum caudolaterale (Ncl) could be distinguished by the high density of its dopaminergic fibers. Retrograde tracer injections into Ncl revealed afferents from the Area ventralis tegmentalis (AVT) and the n. tegmenti pedunculo-pontinus pars compacta (TPc). Since large numbers of DA-like perikarya could be detected in AVT and TPc, it is supposed that these two structures constitute the main source of the dopaminergic innervation of the Ncl. Previous studies had suggested that the Ncl represents an avian equivalent to the mammalian prefrontal cortex. The present results reveal an organization similar to that of the mesocortico-prefrontal system and would thus strengthen this hypothesis.

Right head-turning preference is assumed to be a developmental default. This motor asymmetry seems to influence the development of other lateralised behaviours-such as handedness-as a consequence of orienting vision towards the right side of the body. To document the role of visual experience in promoting lateralised functions we assessed head-turning preference and handedness in a group of congenitally blind human adults. We found a left-side preference for head turning but a clear righthandedness in the same individuals. This asymmetric relationship suggests that absence of visual experience can alter head-turning preference and that handedness can emerge without visual orientation towards the right side. Our findings shed new light on the role of visual sensory experience in shaping functional asymmetries and suggest that single-gene models and environment alone cannot fully explain the emergence of functional asymmetries in humans. © 2013 Taylor & Francis.

Severe feather pecking (SFP) remains one of the major welfare issues in laying hens. SFP is the pecking at and pulling out of feathers, inflicting damage to the plumage and skin of the recipient. The neurobiological profile determining the vulnerability of individual hens to develop into a severe feather pecker is unknown, although brain monoamines such as serotonin (5-HT) and dopamine (DA) seem to play a role. Previous studies related lower 5-HT and DA turnover ratios to an increased risk to develop SFP.In this thesis, monoamine levels in brain areas involved in emotional regulation and motor control were compared between phenotypically and genetically selected high and low feather peckers at different ages. It was found that adult high feather peckers had higher monoaminergic activity (lower metabolite levels and/or turnover ratios) in comparison to low feather peckers, which is in contrast with results on young hens. Differences were seen in several brain areas, namely the dorsal thalamus, medial striatum, amygdala, caudocentral nidopallium, and the somatomotor arcopallium, but to a lesser extend or not in the caudolateral nidopallium and the hippocampus. To investigate the exact neurobiological mechanism behind severe feather pecking further extracellular levels of 5-HT and DA and their metabolites were measured by in vivo microdialysis. Up till now, microdialysis has only been executed in young chickens, but this thesis describes the first microdialysis study performed in adult laying hens. It was found that adult severe feather peckers had a higher baseline release of 5-HT in the caudal nidopallium, a large associative area in the chicken’s forebrain. This result could not be explained by the amount of 5-HT presynaptically stored, as both high and low SFP lines displayed a similar 5-HT release after d-fenfluramine administration. This confirms that genetic selection on SFP has altered the serotonergic system in feather pecking-phenotypes. With clear phenotypic and genotypic differences in brain areas related to emotional regulation and motor control, it can be assumed that brain deficits at a young age increase an individual’s vulnerability to stressful environmental changes, which is associated with the prevalence of SFP later in life. The cause of the inversion of neurochemical patterns in young and adult high and low feather pecking hens remains to be elucidated. Perhaps this inversion is caused by development itself. On the other hand, higher behavioral patterns (SFP and other types of allopecking) observed in the high feather pecking chickens might have influenced the monoaminergic activity since the brain influences behavior and vice versa. Altogether, this thesis demonstrates the importance of considering the impact of genetic selection and also environmental conditions on brain neurotransmission and with that, on the vulnerability of individual chickens to develop SFP. Both the serotonergic and dopaminergic systems are involved in the development of SFP. With SFP being a multifactorial problem both genotype and phenotype have to be taken into account. Furthermore, in vivo microdialysis is a valuable approach to investigate why individual laying hens start SFP. This will lead to further understanding and ultimately in the reduction of SFP.

Severe feather pecking (SFP) remains one of the major welfare issues in laying hens. SFP is the pecking at and pulling out of feathers, inflicting damage to the plumage and skin of the recipient. The neurobiological profile determining the vulnerability of individual hens to develop into a severe feather pecker is unknown, although brain monoamines such as serotonin (5-HT) and dopamine (DA) seem to play a role. Previous studies related lower 5-HT and DA turnover ratios to an increased risk to develop SFP.In this thesis, monoamine levels in brain areas involved in emotional regulation and motor control were compared between phenotypically and genetically selected high and low feather peckers at different ages. It was found that adult high feather peckers had higher monoaminergic activity (lower metabolite levels and/or turnover ratios) in comparison to low feather peckers, which is in contrast with results on young hens. Differences were seen in several brain areas, namely the dorsal thalamus, medial striatum, amygdala, caudocentral nidopallium, and the somatomotor arcopallium, but to a lesser extend or not in the caudolateral nidopallium and the hippocampus. To investigate the exact neurobiological mechanism behind severe feather pecking further extracellular levels of 5-HT and DA and their metabolites were measured by in vivo microdialysis. Up till now, microdialysis has only been executed in young chickens, but this thesis describes the first microdialysis study performed in adult laying hens. It was found that adult severe feather peckers had a higher baseline release of 5-HT in the caudal nidopallium, a large associative area in the chicken’s forebrain. This result could not be explained by the amount of 5-HT presynaptically stored, as both high and low SFP lines displayed a similar 5-HT release after d-fenfluramine administration. This confirms that genetic selection on SFP has altered the serotonergic system in feather pecking-phenotypes. With clear phenotypic and genotypic differences in brain areas related to emotional regulation and motor control, it can be assumed that brain deficits at a young age increase an individual’s vulnerability to stressful environmental changes, which is associated with the prevalence of SFP later in life. The cause of the inversion of neurochemical patterns in young and adult high and low feather pecking hens remains to be elucidated. Perhaps this inversion is caused by development itself. On the other hand, higher behavioral patterns (SFP and other types of allopecking) observed in the high feather pecking chickens might have influenced the monoaminergic activity since the brain influences behavior and vice versa. Altogether, this thesis demonstrates the importance of considering the impact of genetic selection and also environmental conditions on brain neurotransmission and with that, on the vulnerability of individual chickens to develop SFP. Both the serotonergic and dopaminergic systems are involved in the development of SFP. With SFP being a multifactorial problem both genotype and phenotype have to be taken into account. Furthermore, in vivo microdialysis is a valuable approach to investigate why individual laying hens start SFP. This will lead to further understanding and ultimately in the reduction of SFP.