The mismatch negativity (MMN) is a pre-attentive brain response to auditory environmental change. Temporal and frontal cortex generators of pre-attentive change detection have been proposed based on source localization of event-related potentials (ERP), positron emission tomography (PET), and functional magnetic resonance imaging (fMRI) studies. The temporal cortex generators are believed to underlie change detection, whereas the frontal cortex generators are thought to subserve reorientation of attention in response to change. The present study used the event-related optical signal (EROS), an imaging technique that is sensitive to activity related changes in the light scattering properties of neurons, to investigate the pre-attentive brain response to stimulus omissions. The stimulus train comprised 10 ms tone pips presented with a stimulus onset asynchrony (SOA) of 84 ms. Occasional tone omissions elicited a significant increase in right superior temporal gyrus (STG) activity 140 ms after the omitted stimulus, followed 60 ms later by right inferior frontal gyrus (IFG) activity. This result provides support for a temporal-frontal cortical network that underlies pre-attentive change detection.