The brainstem's activity and control over both central and peripheral functioning is notably widespread, yet difficult to quantify due to its location and size. Methods have been developed to improve our understanding of the brainstem's activity, particularly through the use of proxy-measures, via physiologic imaging. Heart rate variation, pupillometry, skin conduction, P300 alterations, and salivary α-amylase are popular measures which allow for a determination of brainstem activity. This chapter discusses the use and findings of physiologic imaging for brainstem activity. It also discusses how researchers may attempt to alter brainstem activity with stimulation. Vagus nerve, occipital nerve, and auditory nerve stimulation are discussed, with their therapeutic contributions and functional effects for context. We discuss evoked brainstem responses including brainstem evoked audiometry, which additionally provide valuable information as a direct representation of brainstem activation and pathology. Lastly, we discuss the application of brainstem responses and nerve stimulation in a surgical setting via intraoperative recording. We conclude by discussing the value of these measures and methods in brainstem research.
