One of the most important brain rhythms is that which generates involuntary breathing movements. The lower brainstem contains neural circuitry for respiratory rhythm generation in mammals. To date, microsectioning and selective lesioning studies have revealed anatomical regions necessary for respiratory rhythmogenesis. Although respiratory neurons distributed within these regions can be identified by their firing patterns in different phases of the respiratory cycle, conventional electrophysiology techniques have limited the investigation of spatial organization within this network. Optical imaging techniques offer the potential for monitoring the spatiotemporal activity of large groups of neurons simultaneously. Using high-speed voltage-sensitive dye imaging and spatial correlation analysis in an arterially-perfused in situ preparation of the juvenile rat, we have determined the spatial distribution of respiratory neuronal activity in a region of the ventrolateral respiratory group containing the pre-Boetzinger complex (pBC) during spontaneous eupneic breathing. While distinctly pre- and post-inspiratory related responses were spatially localizable on length scales less than 100µm, we found the investigated area on whole exhibited a spatial mixture of phase-spanning and post-inspiratory related activity. Additionally, optical recordings revealed significant widespread hyperpolarization, suggesting inhibition in the same region during expiration. This finding is consistent with the hypothesis that inhibitory neurons play a crucial role in the inspiration-expiration phase transition in the pBC. To our knowledge this is the first optical imaging of a near fully-intact in situ preparation that exhibits both eupneic respiratory activity and functional reflexes.