Frontal brain deactivation during a non-verbal cognitive judgement bias test in sheep

Animal welfare concerns have raised an interest in animal affective states. These states also play an important role in the proximate control of behaviour. Due to their potential to modulate short-term emotional reactions, one specific focus is on long-term affective states, that is, mood. These states can be assessed by using non-verbal cognitive judgement bias paradigms. Here, we conducted a spatial variant of such a test on 24 focal animals that were kept under either unpredictable, stimulus-poor or predictable, stimulus-rich housing conditions to induce differential mood states. Based on functional near-infrared spectroscopy, we measured haemodynamic frontal brain reactions during 10 s in which the sheep could observe the configuration of the cognitive judgement bias trial before indicating their assessment based on the go/no-go reaction. We used (generalised) mixed-effects models to evaluate the data. Sheep from the unpredictable, stimulus-poor housing conditions took longer and were less likely to reach the learning criterion and reacted slightly more optimistically in the cognitive judgement bias test than sheep from the predictable, stimulus-rich housing conditions. A frontal cortical increase in deoxy-haemoglobin [HHb] and a decrease in oxy-haemoglobin [O2Hb] were observed during the visual assessment of the test situation by the sheep, indicating a frontal cortical brain deactivation. This deactivation was more pronounced with the negativity of the test situation, which was reflected by the provenance of the sheep from the unpredictable, stimulus-poor housing conditions, the proximity of the cue to the negatively reinforced cue location, or the absence of a go reaction in the trial. It seems that (1) sheep from the unpredictable, stimulus-poor in comparison to sheep from the predictable, stimulus-rich housing conditions dealt less easily with the test conditions rich in stimuli, that (2) long-term housing conditions seemingly did not influence mood--which may be related to the difficulty of tracking a constant long-term state in the brain--and that (3) visual assessment of an emotional stimulus leads to frontal brain deactivation in sheep, specifically if that stimulus is negative.

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