Exploration in outbred mice covaries with general learning abilities irrespective of stress reactivity, emotionality, and physical attributes

Across multiple learning tasks (that place different sensory, motor, and information processing demands on the animals), we have found that the performance of mice is commonly regulated by a single factor ("general learning") that accounts for 30-40% of the variance across individuals and tasks. Furthermore, individuals' general learning abilities were highly correlated with their propensity to engage in exploration in an open field, a behavior that is potentially stress-inducing. This relationship between exploration in the open field and general learning abilities suggests the possibility that variations in stress sensitivity/responsivity or related emotional responses might directly influence individuals' general learning abilities. Here, the relationship of sensory/motor skills and stress sensitivity/emotionality to animals' general learning abilities were assessed. Outhred (CD-1) mice were tested in a battery of six learning tasks as well as 21 tests of exploratory behavior, sensory/motor function and fitness, emotionality, and stress reactivity. The performances of individual mice were correlated across six learning tasks, and the performance measures of all learning tasks loaded heavily on a single factor (principal component analysis), accounting for 32% of the variability between animals and tasks. Open field exploration and seven additional exploratory behaviors (including those exhibited in an elevated plus maze) also loaded heavily on this same factor, although general activity, sensory/motor responses, physical characteristics, and direct measures of fear did not. In a separate experiment, serum corticosterone levels of mice were elevated in response to a mild environmental stressor (confinement on an elevated platform). Stress-induced corticosterone levels were correlated with behavioral fear responses, but were unsystematically related to individuals' propensity for exploration. In total, these results suggest that although general learning abilities are strongly related to individuals' propensity for exploration, this relationship is not attributable to variations in sensory/motor function or the individuals' physiological or behavioral sensitivity to conditions that promote stress or fear. (c) 2006 Elsevier Inc. All rights reserved.