We used functional MRI to test the hypothesis that emotional states can selectively influence cognition-related neural activity in lateral prefrontal cortex (PFC), as evidence for an integration of emotion and cognition. Participants (n = 14) watched short videos intended to induce emotional states (pleasant/approach related, unpleasant/withdrawal related, or neutral). After each video, the participants were scanned while performing a 3-back working memory task having either words or faces as stimuli. Task-related neural activity in bilateral PFC showed a predicted pattern: an Emotion x Stimulus crossover interaction, with no main effects, with activity predicting task performance. This highly specific result indicates that emotion and higher cognition can be truly integrated, i.e., at some point of processing, functional specialization is lost, and emotion and cognition conjointly and equally contribute to the control of thought and behavior. Other regions in lateral PFC showed hemispheric specialization for emotion and for stimuli separately, consistent with a hierarchical and hemisphere-based mechanism of integration.