A system configured to adjust an intensity of sensory stimulation delivered to a subject during a sleep session, the system comprising: means for providing sensory stimulation to the subject; means for generating output signals conveying information related to sleep spindles in the subject during the sleep session; means for detecting the sleep spindles in the subject based on the output signals; means for determining a recent spindle density and/or a recent spindle frequency for a recent period of time during the sleep session based on the detected sleep spindles; means for determining a previous spindle density and/or a previous spindle frequency for a previous period of time during the sleep session based on the detected sleep spindles, wherein a beginning of the previous period of time occurs before a beginning of the recent period of time during the sleep session; and means for controlling the means for providing sensory stimulation to adjust the intensity of sensory stimulation provided to the subject based on a comparison of the previous spindle density to the recent spindle density and/or the previous spindle frequency to the recent spindle frequency, wherein controlling the means for providing sensory stimulation includes increasing the intensity of the sensory stimulation responsive to an increase in the recent spindle density relative to the previous spindle density and/or a decrease in the recent spindle frequency relative to the previous spindle frequency, wherein the recent spindle density and/or frequency is (i) an average density and/or frequency determined based on multiple density and/or frequency determinations during the most recent minute, or (ii) indicative of a relative change in spindle density and/or frequency from the start of the most recent minute to the end of the most recent minute, or (iii) a single density and/or frequency determination, or (iv) based on a single density and/or frequency determination. means for providing sensory stimulation to the subject; means for generating output signals conveying information related to sleep spindles in the subject during the sleep session; means for detecting the sleep spindles in the subject based on the output signals; means for determining a recent spindle density and/or a recent spindle frequency for a recent period of time during the sleep session based on the detected sleep spindles; means for determining a previous spindle density and/or a previous spindle frequency for a previous period of time during the sleep session based on the detected sleep spindles, wherein a beginning of the previous period of time occurs before a beginning of the recent period of time during the sleep session; and means for controlling the means for providing sensory stimulation to adjust the intensity of sensory stimulation provided to the subject based on a comparison of the previous spindle density to the recent spindle density and/or the previous spindle frequency to the recent spindle frequency, wherein controlling the means for providing sensory stimulation includes increasing the intensity of the sensory stimulation responsive to an increase in the recent spindle density relative to the previous spindle density and/or a decrease in the recent spindle frequency relative to the previous spindle frequency, wherein the recent spindle density and/or frequency is (i) an average density and/or frequency determined based on multiple density and/or frequency determinations during the most recent minute, or (ii) indicative of a relative change in spindle density and/or frequency from the start of the most recent minute to the end of the most recent minute, or (iii) a single density and/or frequency determination, or (iv) based on a single density and/or frequency determination. <EOS>