1. A system configured to deliver stimuli to a subject that prompt the subject to transition into a sleep stage, the system comprising: one or more sensors configured to generate one or more output signals conveying information related to one or more parameters associated with brain activity of the subject; one or more processors configured to execute computer program modules, the computer program modules comprising: a parameter determination module configured to determine a first spectral parameter that indicates power in a first frequency band and a second spectral parameter that indicates power in a second frequency band, wherein the first and second spectral parameters are based on the one or more generated output signals, wherein an average frequency of the first frequency band is higher than an average frequency of the second frequency band; a control module configured to control a stimulus source to deliver a stimulus to the subject, wherein controlling the stimulus source includes adjusting an intensity of the stimulus, wherein the adjustment is based on the first spectral parameter and the second spectral parameter.