The 1951-1979 period unified affective neuroscience around a core paradigm in which monoaminergic systems act as broad modulators of emotion and cognition, linking brainstem nuclei to widespread cortical and limbic targets, with amygdala-centered circuits driving emotional learning. The era also charted cortical hierarchies and thalamocortical loops, and documented interlaminar and multisensory networks that support cross-modal processing across species. Neurophysiological and cognitive neuroscience methods—evoked potentials, event-related potentials, and functional anatomy studies—enabled cross-species insights into patterns of cognitive processing associated with affective states. Historical Significance: Landmark demonstrations of the amygdala as a causal hub for fear, social behavior, and affect established a foundational framework for later affective neuroscience, while the anatomy and physiology of central catecholamine systems anchored monoaminergic modulation as a central mechanism for emotion regulation. Early work mapping the receptive fields and functional architecture of the striate cortex in cats and primates provided enduring models of cortical processing, feeding into theories of perception, attention, and reward. Foundational resources for emotion recognition, epitomized by standardized facial affect sets, seeded long-running research on emotion perception and cross-cultural affective neuroscience.