Piloerection in the homecage and imaging environment. The top photograph shows a male and female resident in their homecage moments after the introduction of a novel adult male intruder. The insert shows a photograph of piloerection along the midline back of the male resident. The bottom photograph shows a male resident with his head secured in the animal restrainer used for imaging. The animal's body is unrestrained and the body holder is open at the top to allow visualization of the animal's back. A vivarium designed to fit into the bore of the scanner immediately in front of the male resident is shown housing the resident's female partner and a novel adult male intruder. This presentation of stimulus animals in the vivarium elicits piloerection in the restrained male resident, an autonomic response that can be observed in the bore of the scanner during data acquisition.