A glass full of optimism: Enrichment effects on cognitive bias in a rat model of depression

Abstract

Investigations of cognitive biases in animals are conceptually and translationally valuable because they contribute to animal welfare research and help to extend and refine our understanding of human emotional disorders, where biased information processing is a critical causal and maintenance factor. We employed the "learned helplessness" genetic rat model of depression in studying cognitive bias and its modification by environmental manipulations. Using a spatial judgment task, responses to ambiguous spatial cues were assessed before and after environmental enrichment to test whether this manipulation would cause an optimistic shift in emotional state. Twenty-four congenitally helpless and nonhelpless male rats were trained to discriminate two different locations, "rewarded" versus "aversive." After successful acquisition of this spatial discrimination, cognitive bias was probed by measuring responses to three ambiguous locations. Latencies to "reach" and to actively "choose" a goal pot were recorded alongside exploratory behaviors. An overall strain difference was observed, with helpless rats displaying longer "reach" latencies than nonhelpless rats. This implies a "pessimistic" response bias in helpless rats, underscoring their depressive-like phenotype. No strain differences were observed regarding other behavioral measures. Half of the animals were then transferred to enriched cages and retested. Environmental enrichment resulted in reduced "choose" latencies in both rat strains, associating enrichment with more optimistic interpretations of ambiguous cues. Our results emphasize the suitability of cognitive bias measurement for animal emotion assessment. They extend the methodological repertoire for characterizing complex phenotypes and bear implications for animal welfare research and for the use of animal models in preclinical research.

Touchscreen-paradigm for mice reveals cross-species evidence for an antagonistic relationship of cognitive flexibility and stability

“…The high visual-motoric requirements may therefore overlap with the cognitive operations, challenging the use of response times in this context. This adds to previous discussions about the use of latency measures in cognitive testing (Richter et al, 2012). …”

The Effects of Environmental Enrichment on Depressive and Anxiety-Relevant Behaviors in Socially Isolated Prairie Voles

“…Interestingly, this grooming behavior mirrors the pattern observed in Experiment 1; grooming also was increased as a function of EE, regardless of social housing condition. Studies with other rodent models indicate that both EE and voluntary exercise can reduce depressive and anxiety behaviors (27,30–33). Indeed, exercise also has been shown to have both antidepressant and anxiolytic properties in humans (49–51).…”

“…Although the details of each EE paradigm vary, they are hypothesized to engage similar neuroplastic mechanisms to influence behavior, and previous attempts have failed to attribute the effects of EE to any single variable (24,29). Both EE and voluntary exercise alone reduce anxiety- and depression-like behaviors in a variety of animal models (27,30–33). In the social domain, mice and rats exposed to EE exhibit increased sociability compared to control animals (34,35).…”

Hope for the Best or Prepare for the Worst? Towards a Spatial Cognitive Bias Test for Mice

“…The fact that mice are the premier mammalian model system in preclinical neuropsychological research calls for reliable methods to assess affective states in this species as well. If cognitive biases can be assessed in mice, this may fundamentally increase the translational value of many mouse models and consequently may help to extend and refine the understanding of human emotional disorders [21]. A promising approach in this field has already been made by Boleij and associates, who established a cognitive bias test, in which two distinct odors predicted either a palatable or an unpalatable food reward and the reaction of the mice to a mixture of both odors was used as a measure of their judgment bias [35].…”