A system configured to adjust a volume of auditory stimulation delivered to a subject during sleep, the system comprising: one or more sensory stimulators configured to provide the auditory stimulation to the subject; one or more sensors configured to generate output signals conveying information related to brain activity in the subject; and one or more hardware processors operatively communicating with the one or more sensory stimulators and the one or more sensors, the one or more hardware processors configured by machine-readable instructions to determine brain activity parameters in the subject for a first sleep session based on the output signals, the brain activity parameters including a deepening time indicative of a rate at which sleep of the subject deepens during the first sleep session, and characterized in that the deepening time is determined based on (i) a ratio of power in a high frequency band of an electroencephalogram signal to power in a low frequency band, (ii) a density of slow waves in the subject, or (iii) a hypnogram for the first sleep session, indicative of sleep depth in the subject during the first sleep session; and in that the one or more hardware processors are further configured by machine-readable instructions to: determine a rate of volume increase for auditory stimulation provided to the subject during a subsequent sleep session based on the deepening time; and control the one or more sensory stimulators to adjust the volume of auditory stimulation provided to the subject during the subsequent sleep session based on the determined rate of volume increase and the output signals during the subsequent sleep session. one or more sensory stimulators configured to provide the auditory stimulation to the subject; one or more sensors configured to generate output signals conveying information related to brain activity in the subject; and one or more hardware processors operatively communicating with the one or more sensory stimulators and the one or more sensors, the one or more hardware processors configured by machine-readable instructions to determine brain activity parameters in the subject for a first sleep session based on the output signals, the brain activity parameters including a deepening time indicative of a rate at which sleep of the subject deepens during the first sleep session, and characterized in that the deepening time is determined based on (i) a ratio of power in a high frequency band of an electroencephalogram signal to power in a low frequency band, (ii) a density of slow waves in the subject, or (iii) a hypnogram for the first sleep session, indicative of sleep depth in the subject during the first sleep session; and in that the one or more hardware processors are further configured by machine-readable instructions to: determine a rate of volume increase for auditory stimulation provided to the subject during a subsequent sleep session based on the deepening time; and control the one or more sensory stimulators to adjust the volume of auditory stimulation provided to the subject during the subsequent sleep session based on the determined rate of volume increase and the output signals during the subsequent sleep session.