Anxiety-induced cognitive bias in non-human animals.
ABSTRACT As in humans, 'cognitive biases' in the way in which animals judge ambiguous stimuli may be influenced by emotional state and hence a valuable new indicator of animal emotion. There is increasing evidence that animals experiencing different emotional states following exposure to long-term environmental manipulations show contrasting biases in their judgement of ambiguous stimuli. However, the specific type of induced emotional state is usually unknown. We investigated whether a short-term manipulation of emotional state has a similar effect on cognitive bias, using changes in light intensity; a treatment specifically related to anxiety-induction. Twenty-four male rats were trained to discriminate between two different locations, in either high ('H') or low ('L') light levels. One location was rewarded with palatable food and the other with aversive food. Once the rats had shown spatial discrimination, by running significantly faster to the rewarded location, they were tested with three ambiguous locations intermediate between the rewarded and aversive locations, and their latency to approach each location recorded. Half the rats were tested in the same light levels as during training, the remainder were switched. Rats switched from high to low light levels (putatively the least negative emotional manipulation) ran significantly faster to all three ambiguous probes than those rats switched from low to high light levels (putatively the most negative manipulation). This suggests that the judgement bias technique might be useful as an indicator of short-term changes in anxiety for non-human animals.
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ABSTRACT: Cognitive bias tasks purport to assess affective states via responses to ambiguous stimuli. We hypothesized that a novel cognitive bias task based on positive reinforcement using quantity differences would detect changes in affect in captive grizzly bears (Ursus arctos horribilis). We trained bears (n = 8) to respond differently (nose or paw touch) to two stimuli (light or dark gray cue cards), with responses counterbalanced across bears. The two cues signaled a small or large food reward, respectively. Responses to ambiguous probe stimuli (i.e., shades of gray) intermediate to the trained stimuli were classified as either 'optimistic,' appropriate for the larger reward, or 'pessimistic,' appropriate for the smaller reward. In Experiment 1, we explored the contrast in reward size necessary to detect a change in response across probe stimuli (large reward, 3 or 6 apple slices: small reward, 1 slice). We observed a change in response across probe stimuli, with no difference in response between reward-value groups, indicating that a contrast of 3:1 apple slices was sufficient to affect responses. In Experiment 2, we investigated cognitive bias after 2.1 h of exposure to enrichment items varying in attractiveness. Results were unaffected by enrichment type or time spent interacting with enrichments, indicating that the task failed to demonstrate criterion validity for comparing mood following exposure to different enrichment items. However, greater time spent pacing prior to testing was associated with 'optimistic' judgments. The data provide some support for use of cognitive bias tasks based on quantity differences in animal welfare assessments involving captive wildlife.Animal Cognition 09/2013; · 2.71 Impact Factor
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ABSTRACT: Modulation of short-term emotions by long-term mood is little understood but relevant to understand the affective system and of importance in respect to animal welfare: a negative mood might taint experiences, whilst a positive mood might alleviate single negative events. To induce different mood states in sheep housing conditions were varied. Fourteen ewes were group-housed in an unpredictable, stimulus-poor and 15 ewes in a predictable, stimulus-rich environment. Sheep were tested individually for mood in a behavioural cognitive bias paradigm. Also, their reactions to three physical stimuli thought to differ in their perceived valence were observed (negative: pricking, intermediate: slight pressure, positive: kneading). General behaviour, activity, ear movements and positions, and haemodynamic changes in the cortical brain were recorded during stimulations. Generalised mixed-effects models and model probabilities based on the BIC (Bayesian information criterion) were used. Only weak evidence for mood difference was found. Sheep from the unpredictable, stimulus-poor housing condition had a somewhat more negative cognitive bias, showed slightly more aversive behaviour, were slightly more active and moved their ears somewhat more. Sheep most clearly differentiated the negative from the intermediate and positive stimulus in that they exhibited more aversive behaviour, less nibbling, were more active, showed more ear movements, more forward ear postures, fewer backward ear postures, and a stronger decrease in deoxyhaemoglobin when subjected to the negative stimulus. In conclusion, sheep reacted towards stimuli according to their presumed valence but their mood was not strongly influenced by housing conditions. Therefore behavioural reactions and cortical brain activity towards the stimuli were hardly modulated by housing conditions.Behavioural brain research 03/2014; 267:144-155. · 3.22 Impact Factor
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ABSTRACT: Chronic stress in farm animals can induce detrimental effects in emotional sensitivity and cognitive function, for example, by altering fearfulness and eliciting pessimistic-like judgment. Based on a few experiments carried out on laboratory animals, we suggest that exposing chronically stressed sheep to an enriched environment could alleviate the detrimental stress-induced effects on fearfulness and judgment. Fifteen lambs (Chronically Stressed lambs, CS) were submitted for 7 weeks to a treatment known to induce chronic stress (i.e. repeated and unpredictable exposures to various uncontrollable and aversive events every day and/or night). Fifteen other lambs (lambs exposed to Negative and Positive events, NP) were also submitted to the same stressful treatment and, for the last 4 weeks of the stressful treatment, exposed daily to various positive events, i.e. wool brush, positive contact with humans and anticipation of food by a light announcing daily food distribution. Before the treatment, all lambs were individually trained to spatially differentiate between positive and negative reinforced bucket locations with a go/no-go approach response. At the end of the treatment, each lamb was exposed to a judgment test using the same go/no-go design by offering it three ambiguous and unreinforced bucket locations in addition to the two learnt locations. In addition, lambs were exposed to two standard tests of fearfulness (exposure to novelty and suddenness) and human approach test. NP lambs displayed a positive judgement bias: they approached the bucket placed at the ambiguous location that was closest to the positive one faster than CS lambs (3.0 s ± 0.3 vs. 5.9 s ± 1.6; P = 0.006). NP lambs approached the human more than their counterparts (15.0 ± 1.4 vs. 7.7 ± 1.5 times in human zone during 10 min; P = 0.003) and were also more reactive to novelty and suddenness. Thus, repeated exposure lambs to positive events during a stressful period induces an optimistic-like judgment but also increases emotional reactivity. Further studies are thus necessary before promoting such a positive treatment as a method to alleviate negative effects of chronic stress.Applied Animal Behaviour Science 01/2014; · 1.50 Impact Factor