Paradoxical sleep (PS), in which periods with (phasic) and without (tonic) rapid eye movements are intermingled, is hypothesized to be related to cognitive processing and dreaming. Based on polysomnographic data from 12 healthy subjects, this study focuses on the spectral differentiation between phasic and tonic periods. Phasic PS periods exhibited decreased theta and alpha power in the posterior brain areas suggesting the interference of visual processing related to dream imagery. Phasic PS periods were also characterized by a shift from beta to gamma activity in frontal, central and occipital areas reflecting specific phasic related activation. Together, these findings bring new evidence for the existence of visual imagery and cognitive processing during phasic PS.