The present disclosure relates to modulating neural activity within brainstem circuitry to evoke a certain bodily function (e.g., cardiorespiratory response) in a patient. A controller can configure a light signal (such as an infrared light signal) to deliver an amount of radiant exposure to a specific portion of the brainstem for a time. The specific portion of the brainstem can include brainstem circuitry that is the control center for the certain bodily function. The configured light signal can be delivered to the specific portion of the brainstem by an optrode for the time. During application, the light signal can deliver the amount of radiant exposure to the specific portion of the brainstem to evoke the certain bodily function.