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: Anxious and depressed humans typically view circumstances more pessimistically than non-depressed individuals. Here, we explore the proposal that such cognitive biases also exist in non-human animals, and could be used as novel measures of animal welfare. Specifically, we test the hypothesis that wild-caught captive European starlings (Sturnus vulgaris) are more optimistic in their interpretation of ambiguous stimuli when they are housed in cages designed to promote greater welfare compared with when they are housed in standard laboratory cages. Starlings were trained using a choice procedure to discriminate between two temporal stimuli (2s versus 10s duration light stimulus) associated with outcomes of a different value (instant or delayed food). Next, the birds’ responses to ambiguous, unreinforced stimuli of intermediate duration ranging from 2 to 10s were examined under two housing regimes designed to manipulate the birds’ welfare: big enriched cages versus standard cages (smaller and unenriched). The birds’ probability of classifying an intermediate stimulus as that associated with the instant food outcome was significantly higher in the enriched cage compared with the standard cage. Thus, the birds displayed greater optimism in the face of uncertainty under housing conditions in which other measures indicate better welfare. These findings support the use of cognitive bias-based tasks as a novel, non-invasive technique for assessing affective state in non-human animals.Applied Animal Behaviour Science. 01/2008; 109(2-4):374-383.
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ABSTRACT: The effects of sudden darkness on spontaneous motor activity in an open field and performance in an elevated plus-maze (EPM) were assessed in adult male and female rats. In the open field test, sudden darkness increased total locomotion, locomotion in central squares, rearing frequency (RF), and diminished defecation units (DU). In the dark, total locomotion remained elevated during the 20-min test period, while in the light total locomotion decreased significantly after the fourth minute, in both sexes. All the effects of sudden darkness in the open field test were more pronounced in female rats. In the EPM, sudden darkness increased the number of entries into the open arms, total entries, percentages of entries into the open arms, and time spent in the open arms. The changes were more significant in female than in male rats. These results show that sudden darkness increases general motor activity and suggest it diminishes habituation, fear, and anxiety. The results also suggest that this behavioral shift is sexually differentiated. Sudden darkness emerges as an experimental tool to simultaneously test physiologically-induced increases in spontaneous motor activity and decreases in anxiety.Physiology & Behavior 03/1998; 63(3):451-4. · 3.16 Impact Factor
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ABSTRACT: The present study set out to establish the chronic mild stress (CMS) animal model of depression in male CD-1 mice, a commonly used mouse strain. Mice were exposed to a series of mild stressors (e.g. soiled bedding, paired housing, cage tilt, white noise) presented in a continuous unpredictable fashion. Intermittently, CMS was discontinued and the mice were presented with both water and a palatable saccharin solution (0.1% w/v) in a two-bottle choice test overnight (15 h). Repeated exposure of these mice to the stressors led to a reduction in preference for the saccharin solution. This change in preference was attributed to an increase in the consumption of water rather than a decrease in the consumption of saccharin solution. Over time and with extensive testing, CMS no longer affected performance in the two-bottle saccharin preference test. Treatment with the tricyclic antidepressant imipramine (20 mg/kg i.p., once daily) had a varied effect on the CMS-induced change in preference for saccharin, dependent on the timing of initiation of imipramine treatment. In the first instance, following 5 weeks of CMS where a reduction in saccharin preference was established, treatment with imipramine for a further 5 weeks maintained the stress-induced deficit in saccharin preference. However, using a different approach, pre-treatment with imipramine once daily for 2 weeks, prior to onset of CMS, and co-treatment thereafter, attenuated CMS-induced changes in saccharin preference. Finally, when imipramine treatment was scheduled to begin with the CMS procedure, imipramine failed to prevent the CMS-induced reductions in saccharin preference. Changes in behaviour observed after exposure to CMS may be linked to a stress-induced deterioration of the sensitivity of the mice to a rewarding stimulus. Treatment with imipramine can reduce these behavioural changes but is only effective when given repeatedly prior to onset of CMS.Journal of Psychopharmacology 07/2002; 16(2):115-23. · 3.37 Impact Factor