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Marinsek, N. L., Gazzaniga, M. S., & Miller, M. B. (2016). Chapter 17 – Split-Brain, Split-Mind. In S. Laureys, O. Gosseries, & G. Tononi (Eds.), The Neurology of Conciousness (Second Edition) (pp. 271–279). San Diego: Academic Press.
Abstract: The corpus callosum anatomically and functionally connects the two cerebral hemispheres. Despite its important role in interhemispheric communication however, severing the corpus callosum produces few--if any--noticeable cognitive or behavioral abnormalities. Incredibly, split-brain patients do not report any drastic changes in their conscious experience even though nearly all interhemispheric communication ceases after surgery. Extensive research has shown that both hemispheres remain conscious following disconnection and the conscious experience of each hemisphere is private and independent of the other. Additionally, the conscious experiences of the hemispheres appear to be qualitatively different, such that the consciousness of the left hemisphere is more enriched than the right. In this chapter, we offer explanations as to why split-brain patients feel unified despite possessing dual conscious experiences and discuss how the divided consciousness of split-brain patients can inform current theories of consciousness.
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Lucidi, P., Bacco, G., Sticco, M., Mazzoleni, G., Benvenuti, M., Bernabò, N., et al. (2013). Assessment of motor laterality in foals and young horses (Equus caballus) through an analysis of derailment at trot. Physiol. Behav., 109, 8–13.
Abstract: The conflicting results regarding the study of motor laterality in horses may indicate that there does not exist a proper method to assess the degree and the direction of motor bias in these animals. Unfortunately, even less is known about the development of laterality in horses, and to what extent early manipulations can still exert their effects in adulthood. We propose a new method that can be easily applied at a very early age thus avoiding testing adult horses eventually biased by human handling and/or training. Forty-six horses (29 nine-month-old foals and 17 two-year old horses) were handled since birth bilaterally and housed in groups in wide areas. At the time of the analysis, in order to minimize environmental and sensorial disturbances, each horse was tested in a round pen individually or as dyad mother-foal. The ability/inability to properly execute a circle at trot was then recorded, assuming the direction of derailment, i.e. the cutting of the circle, as an indicator of motor bias. From the results of the study it is arguable that motor laterality in horses is acquired over time: in fact foals tested while their mothers were being subjected to longeing showed a higher percentage of ambidextrous animals, while two-year-old horses appeared biased toward the right (p<0.05). Results are discussed in the light of the scientific knowledge about equine biomechanics, taking into account horses' locomotion that leads to the advancement of the body mass through the activation of a kinetic chain that originates from the hindquarters.
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Bussières, G., Jacques, C., Lainay, O., Beauchamp, G., Leblond, A., Cadoré, J. - L., et al. (2008). Development of a composite orthopaedic pain scale in horses. Research in Veterinary Science, 85(2), 294–306.
Abstract: This study addresses development and validation of a composite multifactorial pain scale (CPS) in an experimental equine model of acute orthopaedic pain. Eighteen horses were allocated to control (sedation with/without epidural analgesia – mixture of morphine, ropivacaine, detomidine and ketamine) and experimental groups: amphotericin-B injection in the tarsocrural joint induced pain and analgesia was either i.v. phenylbutazone administered post-induction of synovitis, or pre-emptive epidural mixture, or a pre-emptive combination of the 2. Inter- and intra-observer reproducibility was good (0.8<K<1). The key specific and sensitive behavioural indices were response to palpation of the painful area, posture, and, of lesser value, pawing on the floor, kicking at abdomen and head movement. Of particular interest was the statistical correlation observed between the CPS and both non-invasive blood pressure (P<0.0001) and blood cortisol (P<0.002). This study established the value of some behavioural and physiological criteria in determining equine orthopaedic pain intensity and clearly demonstrated that pre-emptive, multimodal analgesia provided better management than the two other protocols tested.
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Versace, E., Morgante, M., Pulina, G., & Vallortigara, G. (2007). Behavioural lateralization in sheep (Ovis aries). Behav. Brain. Res., 184(1), 72–80.
Abstract: This study investigates behavioural lateralization in sheep and lambs of different ages. A flock was tested in a task in which the animals were facing an obstacle and should avoid it on either the right or left side to rejoin flock-mates (adult sheep) or their mothers (lambs). A bias for avoiding the obstacle on the right side was observed, with lambs apparently being more lateralized than sheep. This right bias was tentatively associated with the left-hemifield laterality in familiar faces recognition which has been documented in this species. Differences between adult sheep and lambs were likely to be due to differences in social reinstatement motivation elicited by different stimuli (flock-mates or mothers) at different ages. Preferential use of the forelegs to step on a wood-board and direction of jaw movement during rumination was also tested in adult animals. No population bias nor individual-level lateralization was observed for use of the forelegs. At the same time, however, there was a large number of animals showing individual-level lateralization for the direction of jaw movement during rumination even though there was no population bias. These findings highlight that within the same species individual- and population-level lateralization can be observed in different tasks. Moreover, the results fit the general hypothesis that population-level asymmetries are more likely to occur in tasks that require social coordination among behaviourally asymmetric individuals.
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Ahrendt, L. P., Labouriau, R., Malmkvist, J., Nicol, C. J., & Christensen, J. W. (2015). Development of a standard test to assess negative reinforcement learning in horses. Appl. Anim. Behav. Sci., 169, 38–42.
Abstract: Most horses are trained by negative reinforcement. Currently, however, no standardised test for evaluating horses' negative reinforcement learning ability is available. The aim of this study was to develop an objective test to investigate negative reinforcement learning in horses. Twenty-four Icelandic horses (3 years old) were included in this study. The horses were tested in a pressure-release task on three separate days with 10, 7 and 5 trials on each side, respectively. Each trial consisted of pressure being applied on the hindquarter with an algometer. The force of the pressure was increased until the horse moved laterally away from the point of pressure. There was a significant decrease in required force over trials on the first test day (P<0.001), but not the second and third day. The intercepts on days 2 and 3 differed significantly from day 1 (P<0.001), but not each other. Significantly stronger force was required on the right side compared to the left (P<0.001), but there was no difference between first and second side tested (P=0.56). Individual performance was evaluated by median-force and the change in force over trials on the first test day. These two measures may explain different characteristics of negative reinforcement learning. In conclusion, this study presents a novel, standardised test for evaluating negative reinforcement learning ability in horses.
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Mejdell, C. M., Buvik, T., Jørgensen, G. H. M., & Bøe, K. E. (2016). Horses can learn to use symbols to communicate their preferences. Appl. Anim. Behav. Sci., 184, 66–73.
Abstract: This paper describes a method in which horses learn to communicate by touching different neutral visual symbols, in order to tell the handler whether they want to have a blanket on or not. Horses were trained for 10-15min per day, following a training program comprising ten steps in a strategic order. Reward based operant conditioning was used to teach horses to approach and touch a board, and to understand the meaning of three different symbols. Heat and cold challenges were performed to help learning and to check level of understanding. At certain stages, a learning criterion of correct responses for 8-14 successive trials had to be achieved before proceeding. After introducing the free choice situation, on average at training day 11, the horse could choose between a “no change” symbol and the symbol for either “blanket on” or “blanket off” depending on whether the horse already wore a blanket or not. A cut off point for performance or non-performance was set to day 14, and 23/23 horses successfully learned the task within this limit. Horses of warm-blood type needed fewer training days to reach criterion than cold-bloods (P<0.05). Horses were then tested under differing weather conditions. Results show that choices made, i.e. the symbol touched, was not random but dependent on weather. Horses chose to stay without a blanket in nice weather, and they chose to have a blanket on when the weather was wet, windy and cold (χ2=36.67, P<0.005). This indicates that horses both had an understanding of the consequence of their choice on own thermal comfort, and that they successfully had learned to communicate their preference by using the symbols. The method represents a novel tool for studying preferences in horses.
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Christensen, J. W., Munk, R., Hawson, L., Palme, R., Larsen, T., Egenvall, A., et al. (2021). Rider effects on horses' conflict behaviour, rein tension, physiological measures and rideability scores. Appl. Anim. Behav. Sci., 234, 105184.
Abstract: Many breeding organisations include a subjective scoring of rideability by a professional rider into their evaluation of sports horses, but the consistency and reliability of the scoring system is debateable. The aim of this study was to investigate (i) whether professional riders agree in their scoring of rideability, and (ii) whether rideability scores are affected by rein tension, horse conflict behaviour, heart rate, and salivary cortisol, and (iii) whether riders induce different levels of conflict behaviour and physiological responses in the horses. Ten professional, female riders each rode 10 dressage horses (level M German scale; n = 100 combinations) through a standardised dressage test (10 min warm-up followed by a 4-min test) and subsequently scored the horses for rideability on the official 1-10 scale (1 = poor to 10 = excellent) from the Danish Riding Federation. Rein tension, horse heart rate, saliva cortisol and conflict behaviour were measured for each rider-horse pair. The riders were inconsistent in their scoring of rideability to the individual horses, e.g. scores for one of the horses ranged from 1 to 8. There was a significant effect of rider (P = 0.003) and the frequency of conflict behaviour (undesired head movements: P < 0.001, breaking the gait: P = 0.013, and other evasive behaviour: P = 0.032) on rideability scores, i.e. the more conflict behaviour the lower the score. There was no significant effect of rein tension and the physiological measures on rideability scores. However, there was a significant effect of rider on rein tension, horses' heart rate and increases in saliva cortisol concentrations and a tendency for some types of conflict behaviour, suggesting that some riders induced more discomfort in the horses. Future studies could help shed light on which elements of riding style are particularly important for sports horse welfare. In conclusion, this study found a large variation in rideability scores assigned to ten sports horses by ten professional riders. Rideability scores were dependent on the level of horse conflict behaviour, but not rein tension and physiological measures. Further studies are needed to improve the objectivity, consistency and reliability of rideability assessment of sports horses.
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Goursot, C., Düpjan, S., Puppe, B., & Leliveld, L. M. C. (2021). Affective styles and emotional lateralization: A promising framework for animal welfare research. Appl. Anim. Behav. Sci., 237, 105279.
Abstract: The growing recognition of animals as individuals has broader implications for farm animal welfare research. Even under highly standardized on-farm conditions, farm animals show heterogeneous but individually consistent behavioural patterns towards various stimuli, based on how they appraise these stimuli. As a result, animal welfare is likely to be highly individual as well, and studying the proximate mechanisms underlying distinct individual behaviour patterns and appraisal will improve animal welfare research. We propose to extend the framework of affective styles to bridge the gap between existing research fields on animal personality and affective states. Affective styles refer to consistent individual differences in emotional reactivity and regulation and can be predicted by baseline cerebral lateralization. Likewise, animals with consistent left or right motor biases--a proxy measure of individual patterns in cerebral lateralization--have been shown to differ in their personality, emotional reactivity, motivational tendencies or coping styles. In this paper, we present the current knowledge of the links between laterality and stable individual traits in behaviour and affect in light of hypotheses on emotional lateralization. Within our suggested framework, we make recommendations on how to investigate affective styles in non-human animals and give practical examples. This approach has the potential to promote a science of affective styles in nonhuman animals and significantly advance research on animal welfare.
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Bergmüller, R., & Taborsky, M. (2010). Animal personality due to social niche specialisation. Trends in Ecology & Evolution, 25(9), 504–511.
Abstract: The existence of 'animal personality', i.e. consistent individual differences in behaviour across time and contexts, is an evolutionary puzzle that has recently generated considerable research interest. Although social factors are generally considered to be important, it is as yet unclear how they might select for personality. Drawing from ecological niche theory, we explore how social conflict and alternative social options can be key factors in the evolution and development of consistent individual differences in behaviour. We discuss how animal personality research might benefit from insights into the study of alternative tactics and illustrate how selection can favour behavioural diversification and consistency due to fitness benefits resulting from conflict reduction among social partners.
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da Cruz, A. B., Hirata, S., dos Santos, M. E., & Mendonça, R. S. (2023). Show me your best side: Lateralization of social and resting behaviors in feral horses. Behav. Process., 206, 104839.
Abstract: Growing evidence shows a variety of sensorial and motor asymmetries in social and non-social interactions in various species, indicating a lateralized processing of information by the brain. Using digital video cameras on tripods and drones, this study investigated lateralization in frequency and duration of social behavior patterns, in affiliative, agonistic, and resting contexts, in a feral population of horses (Equus ferus caballus) in Northern Portugal, consisting of 37 individuals organized in eight harem groups. Affiliative interactions (including grooming) were more often performed, and lasted longer, when recipients were positioned to the right side. In recumbent resting (animals lying down) episodes on the left side lasted longer. Our results of an affiliative behavior having a right side tendency, provide partial support to the valence-specific hypothesis of Ahern and Schwartz (1979) – left hemisphere dominance for positive affect, affiliative behaviors. Longer recumbent resting episodes on the left side may be due to synchronization. However, in both instances it is discussed how lateralization may be context dependent. Investigating the position asymmetries of social behaviors in feral equids will contribute to a better understanding of differential lateralization and hemispheric specialization from the ecological and evolutionary perspectives.
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