A targeted method for memory enhancement, the method comprising: receiving, by a computer processing circuit (212, 800), a plurality of electroencephalography signals from a first plurality of spatially separated EEG sensors and a second plurality of spatially separated EEG sensors located on the head of a subject that is asleep, wherein the first plurality of spatially separated EEG sensors comprise a plurality of frontal EEG sensors and the second plurality of spatially separated EEG sensors comprise a plurality of occipital EEG sensors; computing, by the computer processing circuit (212, 800), a weighted delta measure (Dw) based on the following expression: D w = D A ∗ G wherein: D = weighted delta power over the plurality of frontal EEG signals; A = alpha power over the plurality of occipital EEG signals; G = gamma power over the plurality of frontal EEG signals and the plurality of occipital EEG signals, wherein the weighted delta measure (Dw) is a first spectral feature indicative of a sleep state of the subject; determining, by a first process (116, 600) of the computer processing circuit (212, 800), the sleep state based on the weighted delta measure (Dw); and upon determining, by the computer processing circuit (212, 800), based on a specific EEG signal (126, 502) that the sleep state of the subject is one of sleep stage 2 or sleep stage 3: triggering, by the computer processing circuit (212, 800), a second process of the computer processing circuit (212, 800); determining, by the second process of the computer processing circuit (212, 800), a transition event of the specific EEG signal (126, 502); delivering, by the computer processing circuit (212, 800), upon determining the transition event, an intervention to the subject designed to evoke a specific neurophysiological change to the subject. receiving, by a computer processing circuit (212, 800), a plurality of electroencephalography signals from a first plurality of spatially separated EEG sensors and a second plurality of spatially separated EEG sensors located on the head of a subject that is asleep, wherein the first plurality of spatially separated EEG sensors comprise a plurality of frontal EEG sensors and the second plurality of spatially separated EEG sensors comprise a plurality of occipital EEG sensors; computing, by the computer processing circuit (212, 800), a weighted delta measure (Dw) based on the following expression: D w = D A ∗ G wherein: D = weighted delta power over the plurality of frontal EEG signals; A = alpha power over the plurality of occipital EEG signals; G = gamma power over the plurality of frontal EEG signals and the plurality of occipital EEG signals, wherein the weighted delta measure (Dw) is a first spectral feature indicative of a sleep state of the subject; D = weighted delta power over the plurality of frontal EEG signals; A = alpha power over the plurality of occipital EEG signals; G = gamma power over the plurality of frontal EEG signals and the plurality of occipital EEG signals, wherein the weighted delta measure (Dw) is a first spectral feature indicative of a sleep state of the subject; determining, by a first process (116, 600) of the computer processing circuit (212, 800), the sleep state based on the weighted delta measure (Dw); and upon determining, by the computer processing circuit (212, 800), based on a specific EEG signal (126, 502) that the sleep state of the subject is one of sleep stage 2 or sleep stage 3: triggering, by the computer processing circuit (212, 800), a second process of the computer processing circuit (212, 800); determining, by the second process of the computer processing circuit (212, 800), a transition event of the specific EEG signal (126, 502); delivering, by the computer processing circuit (212, 800), upon determining the transition event, an intervention to the subject designed to evoke a specific neurophysiological change to the subject. triggering, by the computer processing circuit (212, 800), a second process of the computer processing circuit (212, 800); determining, by the second process of the computer processing circuit (212, 800), a transition event of the specific EEG signal (126, 502); delivering, by the computer processing circuit (212, 800), upon determining the transition event, an intervention to the subject designed to evoke a specific neurophysiological change to the subject.