The present disclosure pertains to a system configured to detect slow waves in a subject during a sleep session. The system generates output signals conveying information related to brain activity of the subject. The system is configured to detect individual sleep stages of the subject, the individual sleep stages including a deep sleep stage; and, responsive to detecting the deep sleep stage, generate a harmonic representation of the output signals for a period of time during the sleep session that includes the deep sleep stage; identify two or more points of significance on the harmonic representation of the output signals; and analyze a shape of the harmonic representation of the output signals around the two or more points of significance to determine whether the shape of the harmonic representation of the output signals around the two or more points of significance corresponds to a shape of a slow wave.