Comparative studies in animal welfare optimize the access and the use of resources and foster unique interdisciplinary research environments. We started comparative studies applying our welfare assessment "toolbox" to measure stress biomarkers in pregnant women and troubled youth. Blunted morning cortisol levels, found in our human subjects at risk of premature births, were comparable to the blunted morning cortisol levels which we reported in chronically stressed sows. We studied aggression, spatial memory and brain gene expression in early-weaned pigs. Premature maternal separation increased aggression, likely, as a result of memory impairment due to stress related damage in the hippocampus and frontal cortex of prematurely weaned pigs. We proposed that the early-weaned pig was a model to study "post-traumatic" stress disorders. We are currently studying two animal models that we, arbitrarily, considered likely candidates to explain some aspects of dysfunctional affective disorders in humans. Dysfunctional affective disorders are the cause of debilitating conditions that compromise human and animal welfare on a global scale. Common to humans and animals are some of the dysfunctional affective disorders such as excessive fear, chronic pain, and anxiety disorders. All of these conditions are life threatening pathologies often associated with changes in the brain in response to traumatic, stressful situations. Our studies of tail-biting in pigs and excessive fear in sheep are in collaboration with our Nordic network and with a psychiatric research team, in Oslo. In our current studies, we are conducting a comprehensive battery of behavioural and physiological tests, brain gene expression studies, gene polymorphism studies in addition to pilot brain imaging measurements. Our ability to understand brain processes using non-invasive techniques, such as magnetic resonance imaging, in healthy and diseased animals will be extremely beneficial to address this very important comparative research area.