Showing papers by "Michael Mendl published in 2008"

Mammalian choices: combining fast-but-inaccurate and slow-but-accurate decision-making systems

Abstract: Empirical findings suggest that the mammalian brain has two decision-making systems that act at different speeds. We represent the faster system using standard signal detection theory. We represent the slower (but more accurate) cortical system as the integration of sensory evidence over time until a certain level of confidence is reached. We then consider how two such systems should be combined optimally for a range of information linkage mechanisms. We conclude with some performance predictions that will hold if our representation is realistic.

Sensitivity to reward loss as an indicator of animal emotion and welfare

Abstract: The scientific study of animal emotion is an important emerging discipline in subjects ranging from neuroscience to animal welfare research. In the absence of direct measures of conscious emotion, indirect behavioural and physiological measures are used. However, these may have significant limitations (e.g. indicating emotional arousal but not valence (positivity versus negativity)). A new approach, taking its impetus from human studies, proposes that biases in information processing, and underlying mechanisms relating to the evaluation of reward gains and losses, may reliably reflect emotional valence in animals. In general, people are more sensitive to reward losses than gains, but people in a negative affective state (e.g. depression) are particularly sensitive to losses. This may underlie broader findings such as an enhanced attention to, and memory of, negative events in depressed individuals. Here we show that rats in unenriched housing, who typically exhibit indicators of poorer welfare and a more negative affective state than those in enriched housing, display a prolonged response to a decrease in anticipated food reward, indicating enhanced sensitivity to reward loss. Sensitivity to reward reduction may thus be a valuable new indicator of animal emotion and welfare.

Towards humane end points: behavioural changes precede clinical signs of disease in a Huntington's disease model

Abstract: The number of animals used in science is increasing, bringing a concomitant obligation to minimize suffering. For animals with progressive conditions, euthanasia at a ‘humane end point’ is advised if the end point is scientifically valid, predictive and accurate. Our aim was to test the hypothesis that behavioural changes would reliably precede clinical signs of disease in a progressive neurological model, using retrospective analysis. We observed 100 pair-housed female R6/1 transgenic Huntington's disease (HD) mice and 28 pair-housed female wild-type (WT) mice in standard- or resource-enriched cages. Disease progression was monitored until one member of each HD pair reached a pre-defined end point based on pathological symptoms (HD end). This mouse was then euthanized together with its cage mate (HD other) and any matched WT pairs. At euthanasia, HD mice had significantly greater absolute and relative organ weights, and significantly higher α1 acid glycoprotein concentrations than WT mice, indicating reduced welfare. HD mice initially showed significantly greater use of cage resources than WT mice but this declined progressively. Steeper declines, and earlier cessation, in the use of some climbing and exploration resources occurred in the HD end mice compared with the HD other mice. Behavioural change can be an early indicator of disease onset.