In the course of the 1970s and 1980s, theories derived from neuropsychological research on the bisected brain came rapidly to achieve the status of common sense in the United States and Canada, inflecting all manner of popular and academic discussion. These theories often posited that the right hemisphere was the seat of creative expression, whereas the left hemisphere housed rationality and language. This article analyzes the political and cultural implications of theories about the split brain. Gender relations, educational reform, management theory, race relations, and countercultural concepts about self-expression all quickly came to be viewed through the lens of left-brain/right-brain neuropsychological research. Yet these theories were often contradictory. On the one hand, some psychophysiological experiments premised that the brain was inherently plastic in nature, and thus self-improvement techniques (like mindfulness meditation) could be practiced to unfurl the right hemisphere’s intuitive potentialities. On the other hand, other psychophysiological experiments concluded that Native Americans as well as African Americans and persons from “the East” appeared inherently to possess more highly developed right-brain talents, and therefore suffered in the context of a left-hemisphere-dominated Western society. In both instances, psychologists put neuroscientific research to political and social use. This article thus connects a story from the annals of the neurosciences to the history of psychological experimentation. It analyzes the critical impact that speculative ideas about the split brain were to have not only on the post-1960s history of psychology but also on what soon emerged after the 1990s as the social neuroscience revolution.